Some notes on Geopolymer, cement, clay bricks unfired, and DIY

Some time back I took a bit of a look at what are being called Geopolymers. Liquid stone mixes. New kinds of cement.

Even noted in passing some other “odd bits” related to it.

All of which implies that a silicate sand, treated with highly alkaline solution, ought to form some soluble silicon compounds; then ‘polymerize’ some silicate back between the sand grains when allowed to dry and neutralize the pH.

Well, some times, some ‘muses’ rest a long time between efforts to move them another step down the road. I’ve been thinking of making an attempt at Liquid Stone all on my own for some time now. At least a couple of years. So about a week ago I started to plot. What materials? Which approach? But then decided another bit of ‘prior art’ research ought to be done. Just in case things had moved forward any, or something I’d missed might show up. Good thing, too. A lot did show up.

But first, a digression on shopping.

I spend several hours on the weekend trying to buy:

A) Strong Base. Lye (NaOH), or even KOH. Lime – CaO or hydrated lime Ca(OH)2 or heck, even Natron – aka Sodium Carbonate Na2CO3

B) Kaolin Clay. Mostly an Aluminum Silicate clay of fairly pure sort.

C) Pure Silicate – some SiO2 based stuff.

The idea being to do “mix and match” on the various stuffs and find out what worked and what was not so good.

Well, seems that the days of my youth when I could regularly buy most of that stuff at the grocery store and hardware store in my little farm town are now far gone. Lowes had “Lime”, but reading the package showed it to be some kind of “Garden Lime” bastard mix of CaO, MgO, CaCO3, MgCO3, and a few other things (some hydrated lime and some other hydrates). Basically, half (assed?) roasted dolomite / limestone. Not lime at all, really. Similarly, lye is essentially gone. There was some Drano, with a load of other stuff in the mix too. Clay? Not on your life. So it goes.

After pondering how many specialty shops and what kind of flags would go up trying to order lye on the internet… I went home to sulk. Pondering a bit more, I started looking for more papers. That’s when I found most of the stuff I’m going to link here.

But today is another day. Some small chips started to fall into place.

First off, I picked up an (expensive) bag of Diatomaceous Earth. It claims 85% Silicate. No idea what the other 15% will be. Then again, the Ancients seemed to work with whatever natural dirt was laying around, so maybe a bit of unknown crap isn’t all that important. Then I stumbled on an article complaining about clumping cat litter and how it was Bentonite Clay. Not quite the Kaolinite most of the research papers talked about, but still, it ought to work OK. At least, if my understanding of what happens is right.

No I’ve not bought the cat litter yet… but I do have a nice bag of diatomaceous earth.

So the basic “recipe” is an alkali of some sort as a catalyst, some clay with Aluminum and Silicate in it (and I hypothesize that most any other metal ions ought to be OK too, so clay with Fe or Mg content ought to work. It came from feldspars or feldspathoid minerals in the first place, so it ought to be willing to return to them…)

Then another paper gave some actual pH values. Looks like many different alkaline / basic materials might “work”. Not just lye, but things like bleach and roasted bicarbonate of soda too. (Roasting bicarb of soda turns it into sodium carbonate. That Natron referenced above. I did this when I was about 10 years old, but had hoped to just buy the stuff.) I can also try some of the drain cleaning liquids, if any of the hydroxide types are still around. Oh, and a web search showed Tractor Supply to have 50 lb bags of hydrated lime for about $3 too; so a car trip can ‘bag’ a bag.

Next weekend I’m planning to pick up the hydrated lime, some drain opener, a box of “washing soda” (sodium carbonate) or maybe a big box of bicarb if I need to roast my own, and maybe even some of that “garden lime” that isn’t quite lime… A stop at the grocery will get me some bentonite clay (that promises to ‘clump’ if I pee on it). All in all, that ought to be enough for a good start. If I see any promising quartz sand, I’ll likely get a bit of it, too.

At that point I figure I have enough “options” to find at least one “mix” that sets up.

Paper Chase

Then tonight I did some more paper chase. Found a very nice paper from India where some guys did basically that very thing. Not as many variations on the catalytic base. (One guesses that lye is still used and available in India. Odd to think that folks in India are less constrained and have more awareness of what to do with materials than folks here in the USA… At any rate, they use lye NaOH for the alkaline basic catalyst.) More importantly, they do a very nice matrix of Bentonite clay (it being cheaper and more available than Kaolin one presumes) with various mixes of fly ash and Silica Fume that is basically a waste product from making raw silicon for semiconductors and metallurgy. I can likely use diatomaceous earth as a substitute for silica fume (both mostly SiO2 very finely divided) and maybe some of that “garden lime” in place of their fly ash and / or cement components. Finally, my varieties of base in place of NaOH. Heck, as aluminum gets used in making feldspars, I could likely even use the Drano that has bits of aluminum in it.

The paper in question is here:

Nice “meat and potatoes” research paper. State the goal ( making strong bricks that they call cubes, with geopolymer instead of traditional cement ) state the materials to try, try all the combinations, document the strength, time to set, etc. Graph and write it all up. Nicely done and likely has saved me a few weekends. I now know what has a shot at working best.

NOVEMBER 2012 ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2012 Asian Research Publishing Network (ARPN). All rights reserved.
K. Srinivasan and A. Sivakumar
Structural Engineering Division, VIT University, Vellore, Tamil Nadu, India

Geopolymer based cementitious binder is one of the recent findings in the emerging concrete technology. The
present study investigates the setting and strength properties of geopolymer mixtures containing binary combinations of
bentonite-flyash, bentonite-cement, bentonite-silica-fume and ternary blends of bentonite-flyash-lime. The effect of lime
and alkali activator (sodium hydroxide) on the geopolymerisation of bentonite was studied systematically. The
experimental results showed that the initial and final setting time of binary mixtures containing bentonite and silica fume
(5%) with alkali activator (NaOH) showed early setting time of 30 minutes compared to other geopolymer mixtures. It was
also noted that compressive strength of ternary mixtures containing 40% bentonite, 30% flyash and 30% lime (M16)
attained the maximum strength of 24.74 MPa at 28 days. The highest rate of strength gain was observed at early curing
period (7 days) for the ternary mixtures (M14) consisting of 80% bentonite, 10% flyash and 10% lime compared to other
mixtures. It can be realized from the experimental study that, geopolymerisation reaction was effective for the specimens
cured at 100°C hot air oven.
Keywords: bentonite, fly ash, silica fume, geopolymer, cement, lime, alkali activators.

AND, the whole paper is there, not just some lame abstract and a demand for $40 to get into the peep show and see if you have been ‘had’ or not…

So now I’m pretty darned sure that some kitty litter with a 5-10% diatomaceous earth and 5-10% “garden lime” when mixed with some added drain cleaner or hydrated lime has a pretty good chance of turning into something about like cement.

There are some other papers also worth reading. Each one with some different points of view. But that one has a down to earth practical bent to it that I found refreshing. No lab grade kaolin for these guys, and no fancy additives. Just things like fly ash that are very cheap waste products. The ideal stuff to turn into a resource. Dirt and chimney sweepings, mixed with some lye; and presto! Very strong usable bricks. Nice. Very nice.

One of the papers indicates that a pH of about 10 or so is enough to catalyze things. Here’s a nice pH scale with some common things on it:

pH scale

pH scale


The implication here being that for some class of geopolymerizing reactions, things like ammonia water might even be enough, or oven cleaner, or bleach. (though not ammonia and bleach together as that releases chlorine gas).

The other papers:

It basically finds that you can use fly ash to make something stronger than (or strong as) regular cement via an alkali catalyzed geopolymer process with pH 12 or so. It is one of those PDFs that doesn’t want to let you cut / past bits and I’m feeling a bit rushed so not going to bother breaking their “copy protection”. (Screen cap would do it, but it’s late…) They get some 150 MPa (or about 21,000 psi) strength mixes. Most cement is about 5 MPa to 30 MPa. Has a nice bibliography too.

They, too, have nice graphs and help point you toward what works and what doesn’t. Czech folks and source, so I’d trust it. Those folks generally have their head on straight.

Some folks from Down Under. Short and nice introduction.

The Geopolymerization Process


Geopolymers are a class of inorganic polymer formed by the reaction between an alkaline solution and an aluminosilicate source or feedstock. The hardened material has an amorphous 3-dimensional structure similar to that of an aluminosilicate glass. However unlike a glass these materials are formed at low temperature and as a result can incorporate an aggregate skeleton and a reinforcing system if required, during the forming process.

The reactants are an alkali metal hydroxide/silicate solution (often referred to as the chemical activator) and an aluminosilicate fine binder (typically with a median particle size in the range 1 micron to 30 microns). The binder or feedstock needs to have a significant proportion of the silicon and aluminium ions held in amorphous phases.

The most common activator is a mixture of water, sodium hydroxide and sodium silicate but other alkali metal systems or mixtures of different alkalis can be used, as can any waste source of concentrated alkali. The solution needs to be concentrated or the end product will be a crystalline zeolite rather than a geopolymer.

Commonly used binders include class F flyash, ground granulated slags or metakaolin, but any fine amorphous aluminosilicate material can be used.


As with conventional organic polymerization, the process involves forming monomers in solution then thermally triggering them to polymerize to form a solid polymer.

The geopolymerization process involves three separate but inter-related stages.

During initial mixing the alkaline solution DISSOLVES silicon and aluminium ions from the amorphous phases of the feedstock. The binder is the primary feedstock but any amorphous phases in the aggregate skeleton (stone or sand particles) will also react during this stage.

In the sol so formed, neighbouring silicon or aluminium hydroxide molecules then undergo a CONDENSATION reaction where adjacent hydroxyl ions from these near neighbours condense to form an oxygen bond linking the molecules, and a free molecule of water; OH- + OH- -> O2- + H2O

(Ref : Hench L L, “Sol-Gel Silica. Properties, Processing and Technology Transfer”, Noyes Publications, 1998)

The “monomers” so formed in solution can be represented in 2-dimensions by;-

– Si – O – Al – O – (poly[silalate]),

or, – Si – O – Al – O – Si – O – (poly[silalate-siloxi]),


where each oxygen bond, formed as a result of a condensation reaction, bonds the neighbouring Si or Al tetrahedra.

The application of mild heat (typically ambient or up to 90 degrees C) causes these “monomers” and other silicon and aluminium hydroxide molecules to POLY-CONDENSE or polymerize, to form rigid chains or nets of oxygen bonded tetrahedra.

Higher “curing” temperatures produce stronger geopolymers. As each hydroxyl ion in the tetrahedral is capable of condensing with one from a neighbouring molecule it is theoretically possible for any one silicon ion to be bonded via an oxygen bond to 4 neighbouring silicon or aluminium ions, so forming a very rigid polymer network. Aluminium ions in such a network require an associated alkali metal ion (usually Na) for charge balance.
Hardened Material

The resultant products are;-

a rigid chain or net of geopolymer

a pore solution composed of water (from the catalytic water initially incorporated in the mix recipe plus water generated as a result of the condensation reactions), excess alkali metal ions and unreacted silicon hydroxide. In the case of sodium based activators this pore solution can be considered as a weak solution of sodium metasilicate, with a pH of about 12. It forms a continuous nano or meso porosity throughout the geopolymer unless removed during poly-condensation.

The physical properties of the hardened geopolymer are influenced by the Si/Al ratio of the geopolymer network. Below a Si/Al ratio of 3:1, the resultant 3D nets are rigid, suitable as a concrete, cement or waste encapsulating medium. As the Si/Al ratio increases above 3, the resultant geopolymer becomes less rigid and more flexible or “polymer-like”. With higher Si/Al ratios, up to 35:1, the resultant crosslinked 2D chains are more suited as an adhesive or sealant, or as an impregnating resin for forming fibre mat composites.

What looks like an interesting discussion board.

Pradeep Rana · Group of Institutions, GUNUPUR
It depends on type of Fly ash you are using, but mostly, 7.5-13.4 (Na2O) : 25-29.6 (SiO2) in sodium silicate is recommended.
Aug 1, 2013

Sanjay Kumar · Council of Scientific and Industrial Research (CSIR), New Delhi
In our understanding, only amorphous fraction of fly ash participates in reaction during early geopolymerisation and remaining acts as an aggregate. If there are free alkali available then the crystalline part participate in reaction which is very slow. Thus deciding a geopolymerisation reaction based on total Al2O3 and SiO2 is misleading sometimes.
Aug 2, 2013

Radhakrishna Krishna · Rashtreeya Vidyalaya College of Engineering
0.35 – 0.4 is the best ratio

A couple of papers give a H/T to Davidovits, then an homage to someone they say figured this out in 1950. A Mr. Chelokovski. Doing a web search doesn’t turn up much on him, so I figure it will need a native language search (or a better transliteration into what is used by more of the English language papers). An interesting “Dig Here!”. Generally, I think this process has been turned up from time to time throughout history. Build a wood fire on a clay riverbank. You get lye over clay. Water it out… maybe someone noticed the ground get hard… Also they were from Iran, so likely closer to the Russian work (and maybe using a variant spelling).

From the “Overkill On The Computer” department (but with some good info in it) comes:

Dali Bondar
Faculty member of Ministry of Energy, Iran

Yes, neural nets…

This, and several other papers, concentrate on the alumina-silicates (and want kaolin clay that is pure in that regard). I suspect that the various other clays with things like Fe and Mg and such in them will also make fine liquid stone, perhaps even make things that look like diorite and granite. Things with more feldspars in them. (Or feldspathoids that have more hydration).

At any rate, the paper claims to find that you can predict a variety of properties based on various ratios of components. Looks well written and generally does a nice job.

A long time ago I had to learn this little graph / chart in a geology class. (Back when I was on a “become a geologist” kick). It’s very informative and not at all as hard as it looks.

QAPF Diagram

QAPF Diagram

Attribution and full sized diagram

The basic idea of this thing is that you get different rocks depending on how much of just a few elements are in the mix / melt. My belief is that you ought to be able to get similar geopolymer rocks with similar element ratios.

A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogic composition. The acronym, QAPF, stands for “Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)”. These are the mineral groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized (recalculated so that their sum is 100%).

So Quartz is SiO2. More diatomaceous earth or Silica Fume, you head toward the Q end, less you move away from it. Alkali Feldspar have more potassium and sodium in their formulas. Use more lye or sodium silicate, you move more that way. Feldspars make up most of the rocks in the world, so it’s worth getting to know them.

Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tectosilicate minerals that make up as much as 60% of the Earth’s crust.

But it isn’t just sodium, potassium, and calcium. You can have other metals in those positions. (Oh, as a sidebar: Notice that most of the rocks of the world have aluminum in them? That’s part of why I’m not excited about aluminum cookware… You are soaked in water that has spent millions of years in contact with aluminum compounds. It’s pretty inert and you are well adapted anyway…) But back at the main point: You can find things like Barium Feldspars too. It’s more a concept than a fixed list…

Then there are the feldspathoids. Almost a feldspar, but some of the ratios are a bit wonky… so it’s “close to a feldspar”, sort of. Nature and rocks are not always precise and orderly… From the wiki: “The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks.” so if your melt was low on silica, you get a feldspathoid instead of a feldspar.

So my assertion would just be that as you mix your “stuff”, you can shift the product around on the QAPF diagram (well, not exactly… it is for igneous rocks and we are making a polymer at lower temps of SiO2 and AlO2, so some bits will vary… but my guess is that things will be rather alike in some ways too.) So too little diatomaceous earth or Silica Fume, your rock will be more feldspathoid like. Put in some extra, more toward the Quartz end of the diagram. And so on.

All purely speculative, but a framework for conceptual investigation.

Oh, and “Cement Chemists” get tired of writing all the O2 and O3 and what all, so they made up their own confusing notation where S isn’t Sulphur, it’s Silicon and so on. As this shows up in some of the papers, here’s a guide to it:

You will see things like C-A-S-H ratios that stands for Ca Oxide, Aluminum Oxide, Silicon Di-Oxide, Water ratios.

C CaO Calcium oxide, or lime
S SiO2 Silicon dioxide, or silica
A Al2O3 Aluminium oxide, or alumina
F Fe2O3 Iron oxide, or rust
T TiO2 Titanium dioxide, or titania
M MgO Magnesium oxide, or Periclase
K K2O Potassium oxide
N Na2O Sodium oxide
H H2O Water
C CO2 Carbon dioxide
S SO3 Sulfur trioxide
P P2O5 Phosphorus hemi-pentoxide

And, on the topic of “been found before”, this tidbit: Seems that in the 1800s a guy figured out how to use this kind of reaction to make silicate mineral paint

While lime-based binders carbonate under influence of carbon dioxide and water silicate-based binders (usually potassium silicate resp. potassium water glass) solidify under influence of CO2 and in contact with mineral reactive partners form calcium silicate hydrates.[1]

As lime paints (aside of Fresco-technique) are only moderately weather resistant these today find application primarily in the field of monument preservation. When mineral colors are mentioned nowadays these are commonly understood to be silicate paints. These are paints using potassium water glass as binder. They are also called water glass paints or Keimfarben (after the inventor).

The special composition of silicate paints grant special properties and qualities. Mineral silicate paint coats are considered very durable and weather resistant. Lifetimes exceeding a hundred years are possible. An example for this is the city hall in Schwyz(Switzerland) which received its coat of mineral paint in the 19th century.
Mineral paint contains aside of inorganic colorants potassium-based alkali silicate (water glass), also known as potassium silicate, liquid potassium silicate or LIQVOR SILICIVM. A coat with mineral colors does not form a layer but instead permanently bonds to the substrate material (silicification).

The result is a highly durable connection between paint coat and substrate. Above that the binding agent water glass is highly resistant against UV light. While organic binders such as dispersions based on acrylate or silicone resin under UV over the years tend to grow brittle, chalky and develop cracks which finally result in damage to paint coats, the inorganic binder water glass remains stable. The chemical fusion with the substrate and the UV stability of the binder are the fundamental reasons for the extraordinarily high lifetime of silicate paints.

Silicate paints require siliceous substrate for setting For this reason they are highly suitable for mineral substrates such as mineral plasters and concrete. They are only of limited use for application on wood and metal, though. The permeability for water vapor of silicate paints is equivalent to that of the substrate. This effectively means that silicate paints do not inhibit the diffusion of water vapor. Moisture contained in parts of a structure or in the plaster may diffuse outward without resistance. This keeps walls dry and prevents structural damage. This addition helps avoid condensation water on the surface of building materials. This reduces the risk of infestation by algae and fungi. The high alkalinity of the binding agent water glass adds to the inhibitive effect against infestation by microorganisms and completely eliminates the need for additional preservatives.

So if you have some rocks to paint, you can paint them with a silicate paint… This gives me some ideas for how to make that permanent library of wisdom. Some nice silicate rock tiles then just silk screen the suckers with silicate paint…

This is another of the Iranian papers. Again well written. Similar to the other one.

Amir Kamalloo, Yadolah Ganjkhanlou, Seyed Hamed Aboutalebi and Hossein Nouranian*
Materials and Energy Research Center, P.O. Box 14155-4777, Tehran, Iran,,,
*Corresponding Author
(Received: December 19, 2009 – Accepted: July 15, 2010)
The results showed that
optimized condition of SiO2/Al2O3, R2O/Al2O3, Na2O/K2O and H2O/R2O ratios to achieve high CS
should be 3.6-3.8, 1.0-1.2, 0.6-1 and 10-11, respectively. These results are in agreement with probable
mechanism of geopolymerization.
Keywords Artificial Neural Network, Overfitting, Geopolymer, Compressive Strength, Metakaolin

Points out just how much silicate chemistry matters to the earth surface

The Silicates are the largest, the most interesting, and the most complicated class of minerals by far. Approximately 30% of all minerals are silicates and some geologists estimate that 90% of the Earth’s crust is made up of silicates. With oxygen and silicon the two most abundant elements in the earth’s crust, the abundance of silicates is no real surprise.

So when you add in the other odd silicates, it jumps up to 90% of the crust… The list of minerals is nice to look over. It has things like more of the Iron silicates and things like zinc and zirconium silicates (zircon). I think this points out that in theory you could use all sorts of odd clays and still get some kind of rock out of it.

These folks are looking to use geopolymers to make biomedical bits. Think things like teeth and bones and such. It also lists particular formulas.


In this study three different geopolymer compositions have been investigated and characterized as potential biomaterials. The first two geopolymer formulations are mainly composed of metakaolin, with some silica additions in order to achieve a Si/Al molar of 2.10 while the third one contains a reduced amount of metakaolin and comprises mainly of silica gel with composition: H24AlK7Si31O79 with Si/Al = 31. Further, NaOH pellets and sodium silicate (Na2SiO3) were added in the first two formulations in different concentrations as activator and ligand, respectively, while KOH additions were made to the third geopolymer formulation (separately or jointly with potassium silicate solution). Room temperature consolidation was followed by thermal activation of composition with Si/Al=31 at 60 °C for 150 min and at 500 °C for 180 min.

These folks look at adding “phosphorus slag”. I don’t know why you would have that laying around, but if you do, it can be made into synthetic rocks too…

In this study, metakaolin plus different weight percent of phosphorus slag (10-100 wt. %) were used in preparation of
geopolymer. The compressive strength, phase analysis and microstructure changes were compared with a metakaolin based
geopolymer control sample. Results showed that the substitution of slag up to 40 wt. % instead of metakaolin increase the
28 days compressive strength (14.5 %) compared with control sample. This enhancement of strength is related to coexistence
of geopolymeric gel and C‒S‒H gel or C‒A‒S‒H phase by XRD and FTIR study.

This is someone’s thesis. Looks at both sodium and potassium activated formation. Has a nice bit of historical review, some methods, and the usual bibliography of a Masters Thesis. We also get a couple of more ideas how to find earlier work (but after the Egyptians and Roman Pozzolan methods… we do seem doomed to keep forgetting and reinventing this one.)

Geopolymers recently emerged as a new class of inorganic aluminosilicate polymeric materials. These materials were synthesized for the first time in 1940 by A. O. Purdon [1] and again in the late 1950‘s by Glukhovsky [2]. The term geopolymer was introduced by Davidovits [3] in the early 70‘s to denote their inorganic nature (“geo”) and structural similarity to organic polymers (“polymers”), and is commonly used nowadays

We also get a bit of confirmation of the flexibility and that the speculation about Ammonia might even be viable:

The activating solutions are based on aqueous solutions of alkali hydroxides and the most commonly used metal alkaline activators are Na and K [5]. However, other metals from group I and II of the periodic table as well as NH4+, and H3O+ may also be utilized for synthesis [6, 7]. The silicon content of the final product can be manipulated by the addition of SiO2 to the alkaline aqueous solution.

This guy finds that adding sand makes it stronger. Plenty of room here to play with quartz sand vs feldspar sand too…

The effect of adding sand (40 wt%) on their mechanical properties was also determined. The K1c values increased upto 65% and E values increased upto 80%compared to samples free of sand. However, CCS and MORvalues did not change much and gave mixed results.

And, of course, the one we started with:

That still has some wonderful images in it. I also like the way his recreation of the Egyptian method is so simple:

Lime, Clay, Natron.

But the most interesting point is that this chemical reaction creates pure limestone as well as
hydrosodalite (a mineral of the feldspathoids or zeolites family). [6]

Chemical reaction1:
Si2O5,Al2(OH)4 + 2NaOH = > Na2O.2SiO2Al2O3.nH2O
kaolinite clay + soda = > hydrosodalite

Chemical reaction 2:
Na2CO3 + Ca(OH)2 = > 2NaOH + CaCO3
Sodium carbonate (Egyptian natron) + lime = > soda + limestone
Summary of the re-agglomerated stone binder chemical formula:

clay + natron + lime = > feldspathoids + limestone (i.e. a natural stone)

Now I doubt those old Egyptians were hunting all over for pure Kaolin Clay, and I’d bet their lime and natron were simple burned limestone and burned sodium carbonate. All in all, a pretty simple approach. It also gives a mix of silicate and CaCO3 “gel” as the binder. One of the papers above found having some added calcium around increased strength.

So I’m pretty sure that “old way” ought to work reasonably well. In theory, just a mix of “garden lime”, with some “washing soda” and a bit of “clay kitty litter” ought to work. I’m certainly going to give it a try and find out. Note that reaction 2 makes lye as an intermediary of the overall process. Precipitate some limestone ‘gel’ and get some free lye to catalyze the silicate step. Likely a bit of heat to help it along too. I’ll likely hunt up some nice iron rich red clay and see how it does too. Supposed to be widely sold for dressing baseball diamonds…

Never thought I’d find a way to tie baseball field maintenance to cat latrines to ancient Egyptians and modern waste disposal / recycle… and even making pots for plants on up to bridges and buildings; but it looks like those things are all bound by a common thread. One made of silicates and alkali.

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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47 Responses to Some notes on Geopolymer, cement, clay bricks unfired, and DIY

  1. Geoff Sharp says:

    Hi Chiefio, I was wanting send you something off topic but failed to find an email address of “tips’ page.
    Maybe I didnt look hard enough but thought a recent discovery I made might interest you. I think there is some doubt on the accuracy of the solar proxy record along with dendrochronology and carbon dating in general. The planets have finally given us the key for true calibration of the timeline.

    It goes:

    My recent knowledge given to me by McCracken shows that he 10Be record uses the 14C record to base its timeline due to poor dating precision of ice cores. So one record is piggy backed on another with the 14C record also not beyond question. 14C relies on dendrochronology dating which is far from perfect, and I think I can show is at least 10% incorrect.

    New research has uncovered the accuracy of the 4627 year cycle of the Jovians, this cycle will not repeat forever, but is of use over the Holocene. I have found that the outer planets return to their positions within 2 deg over 4627.25 years, which is very close in astronomical terms, and if the planet positions control the Sun we should expect repeating patterns over the Holocene.

    The LIA is the largest and deepest solar downturn of the Holocene, and if we go back 4637 years we should see the same? (aka -3155)

    The planet positions are almost identical along with the solar path but the solar proxy record shows extreme solar maxima?

    But if we go back another 340 years we find a similar LIA period. I suggest the dating method of the 14C record and beyond is bogus.

  2. R. de Haan says:

    Thanks for both articles E.M and Geoff. Great reads.

  3. R. de Haan says:

    In order to control coastal erosion in area’s with soft coasts but sandy beaches we need a very cheap DIY mix that turns sand into hard rock so people can protect their own homes from crashing into the sea. Any idea’s?

  4. Les Johnson says:

    Chiefo: The oil industry is also working on geopolymers. I know of a Norwegian effort to develop it, as a replacement for cement in abandooning oil and gas wells.

    The geopolymers have the added advantage, I am told, of being self healing. If thermal, pressure or tectonic forces cracks the geopolymer, it will heal, as long as the fracture interfaces are in contact with each other.

  5. Jason Calley says:

    Diatomaceous earth, huh? You haven’t been talking to spirits of ancient Egyptians, have you? Turns out that Michel Barsoum (an expert on electron microscopy and ceramics analysis) examined some samples from the Great Pyramid and found that they used diatomaceous earth! http://www(dot) (replace the “dot”)

    If you want diatomaceous earth for small tests, check your feed and seed store. Many people feed it to horses as a mineral supplement. Also, pool supply stores carry diatomaceous earth — but note that pool D.E. is NOT food grade. It has been heat treated to make it more glassy and while it is not poisonous, it will abrade the heck out of teeth and gut.

    Lye — yes, getting very difficult to find locally, but you can order fairly large quantities from some of the stores that cater to Amish soap makers. On the other hand, if you are just going to make sodium silicate anyway, and are just doing a small batch, go to the auto parts store and buy some radiator sealant. Check the labels and you will probably find one that is almost pure sodium silicate.

    Here is some info on a geopolymer (alumino-silicate) paper from 1940:

    Here is some info on “Grancrete” which seems to be a phosphorous type geopolymer.

    Five or six years ago I actually tried (unsuccessfully!) making some geopolymer from drain cleaner, sand and kitty litter. I think that I did not make a good water glass, so the mixture refused to harden. I have since found that a strong lye solution near boiling will actually dissolve pieces of glass.

    Please keep us posted on any results you get!

  6. agimarc says:

    Thinking about the use of diatomaceous earth vice the use of silica fume in these mixtures. Like fresh volcanic ash, diatomaceous earth is very rough at the microscopic level; lots of surface area for reactions / bonding. OTOH, silica fume is spherical at the microscopic level. All other things being even, a mixture with diatomaceous earth ought to be stronger, perhaps even measurably stronger. Would have to test it to prove it though. Geopolymers are really fun stuff.

    Last bit of who cares stuff is that diatomaceous earth is used up here as a technique to defend gardens from slugs. They don’t like the jagged edges of the individual particles and tend to avoid it much like fresh volcanic ash. Cheers –

  7. Mike Brown says:

    Apparently Red Devil lye is no longer marketed. We used to carry it at the hardware store where I work. Safety was supposedly the reason for withdrawal. NaOH is reputedly used in the manufacture of certain illegal substances, and that may have had something to do with it also.

    To save you a visit from DEA or BNDD, I looked it up for you. (There *is* a list, and *everyone* is on it.)
    in Sebring has it (food grade) for < $2.00/lb.

  8. Zeke says:

    Chief, Ward’s Science carries kaolinite. I bought some some time ago
    Item: 460995 – Kaolinite, Powdered Clay Mineral, 500 g – – 1 – $10.89

    It is a very interesting mineral. I ran a few tests with it and keep meaning to write up the results. Now back to the rest of the article.

  9. Zeke says:

    “At any rate, they use lye NaOH for the alkaline basic catalyst.) More importantly, they do a very nice matrix of Bentonite clay (it being cheaper and more available than Kaolin one presumes) with various mixes of fly ash and Silica Fume that is basically a waste product from making raw silicon for semiconductors and metallurgy. I can likely use diatomaceous earth as a substitute for silica fume (both mostly SiO2 very finely divided) and maybe some of that “garden lime” in place of their fly ash and / or cement components. Finally, my varieties of base in place of NaOH. Heck, as aluminum gets used in making feldspars, I could likely even use the Drano that has bits of aluminum in it.”

  10. LG says:

    Stumbled unto a trove of geopolymer papers:

  11. R. de Haan says:

    This blog is turning into a super WIKI.

  12. Graeme No.3 says:

    suppliers of chemicals for industrial cleaners may be a source for you.
    Sodium metasilicate is a bulk chemical available either as a solid or in liquid (water) solution.
    Water glass /sodium silicate is silicate condensed into short chain forms (starting polymerising).
    Sodium hydroxide is usually bought as a solution (25 or 50%) to avoid the heat/safety problems of dissolving it.
    Sodium triphosphate is the cheapest form of alkaline phosphate. There are tripolyphosphate and tetrapyrophosphate forms, but they are more expensive and break down to the normal phosphate form in water (slowly).
    Al the above are available in potassium versions as well.

    PQ Corporation is the big noise in silicates but probably uninterested in anything less than ten ton lots. Thatcher Chemical, Seidler Chemical look possibles. (Also for diatomaceous earths/kaolins etc.) They may also know of local (Florida) distributors.
    Lintech International sell Feldspar/diatomaceous earths/kaolins/micas/talc/bentonite etc.

    Silica fume might be fumed silica a.k.a. Cabosil, Aerosil etc. very fine particle size silica used for reinforcing rubbers (tyres), thickening paints and unsaturated polyester resins (fiberglas), as a way of making detergents easy flowing & others (don’t ask why they’re in fish fingers).

    Hope this helps.

  13. Wayne Job says:

    According to my book on how to do everything for yourself after the end of civilization.
    You only need lye and animal fat to make soap.
    Making your own lye that will take your skin off is as easy as pie.
    Take an old steel drum and fill it with wood ash from any wood fire source.
    Sit up on bricks with a hole punched in the bottom.
    Pour water over the ashes and collect it at the bottom.
    Depends how strong you want it how many times you cycle the water through the ash.
    Instant lye.

  14. Bloke down the pub says:

    I used to make bio-diesel and bought lye from a local industrial chemical supplier. They never seemed too concerned what I was using it for, nor the methanol that we bought 200lts at a time. I always half expected a visit from the boys in blue.

  15. Coldish says:

    “Diatomaceous Earth. It claims 85% Silicate.”.
    I think they meant silica (Si02) rather than silicate (compounds containing silica).

  16. adolfogiurfa says:

    Coke pH= 3,5 (ACID)

  17. adolfogiurfa says:

    Diatomaceous Earth, as you know is a Diatom fossil. Aluminum,Calcium Silicates. Instead SILICA SAND is almost pure SiO2.

  18. John F. Hultquist says:

    Fine white silica is found as beaches along the Gulf Coast. I have a small bag sent from a friend when she was living in Sarasota but I’ve lost the name of the specific beach. Most from the Tampa Bay area on north are similar, I think.

    Diatomite has been mined in central Washington State, near the town of George, for hundreds of years. When stick houses were being built 100 years ago the walls would be filled with crushed material. An electrician I know cut a hole in a wall near the baseboard and about a bushel of the stuff poured out onto the floor.
    Some local Diatomite has Arsenic mixed in (tiny amounts) and because one of the major uses has been to filter wine and other acidic liquids, testing and processing was required. Many such users have migrated to ceramic membrane systems.
    The white at the coordinates here 46.97796, -119.90897
    is a mine and there are more to the north of I-90. Most older ones have been filled, covered, and re-vegetated. The local plant (16419 Road 10.5 NW Quincy, WA 98848)
    is here:
    47.2394, -119.8392
    The HQ is Imerys Minerals of CA, Lompoc

  19. Jason Calley says:

    I was thinking about what I may have around the house for making some synthetic stone this weekend. I have diatomaceous earth. I have sodium bicarbonate which I can heat to make natron (sodium carbonate). I also have some old radiator leak sealer made of sodium silicate, if I can find it out in the back shed. But I do not have any kaolin or bentonite. On the other hand, I do have some root killer that is almost pure copper sulfate. I was wondering whether I could use the copper in place of the aluminum, and in looking around I found this nice article on ancient Egyptians using “Egyptian Blue”, a calcium-copper-silicate.

    Begin quote:

    Several experiments have been carried out by scientists and archaeologists interested in analyzing the composition of Egyptian blue and the techniques used to manufacture it. It is now generally regarded as a multi-phase material that was produced by heating together quartz sand, a copper compound, calcium carbonate, and a small amount of an alkali (plantash or natron) at temperatures ranging between 800 and 1000 °C (depending on the amount of alkali used) for several hours.[10] The result is cuprorivaite or Egyptian blue, carbon dioxide and water vapor:

    Cu2CO3(OH)2 + 8 SiO2 + 2 CaCO3 → 2 CaCuSi4O10 + 3 CO2 + H2O

    In its final state, Egyptian blue consists of rectangular blue crystals together with unreacted quartz and some glass. From the analysis of a number of samples from Egypt and elsewhere, it was determined that the weight percentage of the materials used to obtain Egyptian blue in antiquity usually ranged within the following amounts:[10]

    60–70% silica (SiO2)
    7–15% calcium oxide (CaO)
    10–20% copper(II) oxide (CuO)

    To obtain theoretical cuprorivaite, where there are only blue crystals, with no excess of unreacted quartz or formation of glass, the following percentages would need to be used:[10]

    64% silica
    15% calcium oxide
    21% copper oxide

    End quote:

    Well, they are describing a high temperature formation — but maybe that is primarily to get the natron to dissolve the silica. If the silica is already dissolved (let the natron – diatomaceous earth – water mixture sit and activate first) maybe I could get a reaction to go at lower temperature. I still need some source of calcium though. I wonder if the wife has some pickling lime?

  20. E.M.Smith says:

    @Jason Calley:

    Yes! For small batches, pickling lime! Sold at Walmart in the canning goods section.

    I’d expect that you could make a copper silicate via a geopolymer route just by using a Cu compound for one of the reactants. So a Cu substitute for Al in one of the geopolymer recipes.

    @John F. Hultquist:

    When I get to the point of making big batches, that could come in handy. For now I’m going to be playing with ounce sized tests. At least, I’ll be doing that as soon as I’ve got a bit of time. (Some car issues sucked up the ‘free time’ for play this week / week-end… Seems nobody in Orlando wants to work on / tune up a 1979 German car. Finally found one guy… but that’s for another day…)


    Yup. I’m planning to get “one each” of whatever sand is sold in the local hardware store. Someday I’ll pick up the wild stuff by the bucket, but for now I want an ingredient list…


    Yes, I was being lazy… re-reading the bag more carefully, it explicitly says:
    Silicon Dioxide 85%

    I presume the rest is some other mineral commonly found in diatom bodies and that I can find that by researching diatoms…

    @Bloke Down The Pub:

    At one time a local chemical supply company was willing to sell me MeOH by the 55 gallon bbl cash and carry. (“Local” in San Jose, Ca.) Last time I asked, they wanted some quantity of paperwork. No idea if that’s changed once one leaves California.

    Also found some lye drain cleaner, though the local “Science Shop” wanted ID and records sent to the Federal Government for GLASSWARE(!), along with any lye or R-12. The “story” was that all three were used in some arcane drug fabrication pathway. Sigh. So much fuss and bother when the simplest path to drugs is stick a seed in a pot and add water… Oh Well…

    Scales measure more accurately than beakers anyway, and pyrex measuring cups are dandy reaction vessels. Sometimes I think that most people have some kind of fundamental dementia cycling around “power trips” and imagining they can control things that can not be controlled. Heck, since ANY gas that dissolves in a fat causes anesthesia, just about any hydrocarbon gas can be used as a drug. (With attendant high risks of death and damage…)

    Maybe the world needs a synthesis pathway that uses salt, beef, and rice. Just to cause TPTB to have their heads explode! ;-)

    Oh Well. Since I can make explosives from battery acid, cotton shirts, and just about any nitrate source, not seeing how it helps to make other stuff hard to get… Did it in the ’60s before it was illegal to play with such stuff. Found the formula in a book from the late 1800s / early 1900s in the library. Adapted it to cotton cloth rather than raw cotton ;-) It’s not hard, but not interested in “sharing” in a public forum. Makes a very nice “gun cotton”, and with a bit of solvent that can become cordite. Somehow the notion that this is technology from the 1500’s to 1800s and based on crude materials and methods is lost on the law making folks. It’s not exactly “high tech”… and doesn’t need modern lab gear or materials.

  21. E.M.Smith says:

    @Geoff Sharp:

    The email address is there in words. But “no worries”. Besides, I’ve not been able to check that email for weeks… Posting here is fine. Solar proxy record, eh? I’ve seen a lot of “issues” in most all the data we’ve got, but not looked at the solar stuff yet. Figured those guys were more reliable… Maybe not…

    From what I’ve seen of the C14 dating, it has a lot of “issues” that are admitted, then ignored. Not the least of which is that the ratios change with a variety of natural processes (like ocean temps and volcanoes and plant growth and…) So it’s “pretty good” up close (until the Nuclear Age blows it) and ever worse going back in time until it is completely useless. Oh, and the assumption is that radiation levels are pretty stable when they are not…

    I’ll take a look at your link. Yes, one of the “games I play” is “pin the date on the next ice age”. My best guess is anywhere from about 375 years from now, to “starting now” to “started in the L.I.A. and we had a periodic bump up, that’s ending now.”

    @R. de Haan:

    Regular concrete is mostly sand and stones. You can just change the mix to all sand and it still works. So something like 1/6 cement, 5/6 sand ought to work. For a geopolymer, it would take a strong alkali and / or some lime. It would depend a bit on the chemical type of the sand. I’d expect the Egyptian formula to work. CaO with Na2CO3 and add sand… Worth a try.

    @Les Johnson:

    Interesting. Self healing may depend on the particular kind of stone. Still, “pressure welding” ought to work for some kinds of stone. Sandstone is made that way, after all…

    @Jason Calley:

    Oh, the Amish! That’s my excuse… I can tell the DEA that I was exploring my heritage of Amish Soap Making! ;-) (Well, only 1/2 ;-) as I DID explore soap making as a kid, and did again about 16 years back, and would make more today if it was easy to grab lye at the grocery store…)

    But I’ve been meaning to try DIY lye making anyway (to get back to the original Celt way of making soap) and part of me wants to stay close to the Egyptian methods that did not involve buying a can of Red Devil Lye at the grocery store. ;-) So maybe just mixing some wood ashes into a stone formula would be enough…

    Diatoms in the Pyramids, eh? Hmmmm…. Wonder how diagnostic that is compared with natural limestones….

    Paper from the 1940s eh? That’s before Davidovits…. Some of the Pozzolans of Roman era formulas look like they use some of the same reactions. To me, it does look like there’s a large body of “techniques” from down the ages that use some part of the “geopolymer” chemistry / method; but just not understood / categorized as all being “of that form”. Each a kind of poorly understood magic formula. Have to look at the paper a bit later (still reading comments now).

    It does look like a “History of Geopolymer Use” would be an interesting semi-technical paper or posting…

    One of the papers above lists formulas that need to be heated to work. I think your formula is close to one of them. I think that some amount of CaO or CaCO3 is needed for the cold set, at least the Egyptian ones. But yes, as I get something done, I’ll post formula, method, and results.


    I got my D.E. from Loews as a bug killer. $8 for about a gallon bag. Expensive, but convenient.

    BTW, the reason I got it has to do with Jason’s formula that didn’t work so well. What you pointed out. Surface Area. Sand is lower surface area, so slower reaction / weaker reaction. It is also a mix of “who knows what”. Diatoms are a known stuff, and very thin section, so very reactive. I figured I’d start with the more reactive end of things and expect to get it to work fast, then slowly back off each element until it stopped.

    @Mike Brown:

    Thanks! I may yet order some from somebody. But I’d rather pay cash and wear a long hat ;-)


    Nice to know. I’m likely to hit up a local “pottery supply shop” first. I really don’t like mail order. If things are not what you expected, it’s just a pain…

    Then again, I buy stuff mail order sometimes anyway…

    BTW, love the comic strip! Reminds of those word definition games where you do things like turn BLACK into WHITE via a series of intermediary changes.

    I did recognize the “well, don’t have that, try this” process as a, um, quirk of mine ;-) Mostly it works. Sometimes you get surprises. A few of them are even nice surprises…


    Nice! Guess I’m not sleeping tonight ;-)

    Hey, I already got a posting up, so now I can get sucked down the paper trail rabbit hole… ;-)

    @R. de Haan:

    “Super-Wiki” of things that interest me ;-)

    Notice you don’t find much about things like double entry book keeping or the use of lace in 17th Century Europe or “modern dance”…

    @Graeme No 3:

    It will be useful for anyone wanting to do big batches. Maybe for me sometime too.

    For now, I’m just hoping to get enough well defined ingredients to get something to work, so I have a baseline. Then work toward “primitive formulas”. I’m most interested in recreating ancient techniques, rather than doing modern whizz-bang super pure chemistry. So starting with some radiator silicate and some pure diatom skeletons is a nice start, but the goal would be to work backward to some kind of “Egyptian ash pile, mixed with rough natron, added to limestone sand or rotted granite”. The kind of thing you can do with a bonfire, some natural rocks, and a bit of carbonates.

    BTW, one of the linked articles went to some length to point out that silica fume is NOT the same as fumed silica. One is a waste product of silicon manufacture and refining for semiconductors (and is about the size of smoke particles) while the other is a product of spattering something or other (so larger particles). Both can be used, though; so not sure it matters all that much to me ;-)

    @Wayne Job:

    I’ve been meaning to find that book ;-)

    I’ve read about doing that to make lye. Been meaning to try it, but never got a round-tuit. Always wondered if it really was that easy. Then again, folks were doing this in pre-history, so maybe it is that easy… I understand there can be some kind of concentration by boiling step to make a saturated solution, but “spatter” is an issue …

    I suspect that “wood ashes” can just be put directly into the mix. Frankly, my hunch is that is exactly what the Egyptians did and maybe how the process was discovered. LOTS of ashes were made in all their chemical processes from making metals and ceramics. Dump a load of ashes in with some ‘trash’ crushed limestone / machining chips and a bit of dirty Natron unsuited to embalming… add a touch of rain. Now your “trash heap” gets a big lump of rock in it. Hmmmm….. now what did I throw away there?…. I’m planning to work backwards from “known to work” pure form to a point where I can test that idea with “likely to work but natural” ingredients. Like wood ashes and some carbonates….

    Hope to give it a try sometime tomorrow, after another run to the hardware store / kitty litter stop. We’ll see if I end up just reading all the links above ;-)

  22. E.M.Smith says:

    Oh, and probably worth noting that an old technique at building sites is to spread lime and work it into the top layer of the soil. It stabilizes the loose dirt / sand and makes it a bit more resistant to forming mud. Better and easier to drive trucks over it and build on it. Not like concrete, but not like bare dirt either. And very very cheap. My belief is that this makes a very poor and porous ‘geopolymer’ spread through with loads of unreacted dirt. It is not durable, but not exactly short lived either. The usual explanation is that you are making a caliche like carbonate, but I think nobody has really analyzed what really happens. That’s part of why I think some kind of lime is important to the easy / simple geopolymers.

  23. I looked quickly through the post. Surprised you did not mention the Geopolymer Institute and Prof Davidovits (although linked by LG in comments) see here For your interest you should have a look at the paper on the Pyramids It seems that there have been more recent papers confirming that the Pyramids were made of poured blocks rather than hewn stone. I have given talks about geopolymers and the pyramids. I have a slide of the roof of one of the burial chambers which clearly shows the outline of wooden planks with recessed carved stars used for formwork. However, still more amazing is some of the thin vases made from a poured material with a composition to diorite which is hard and could not have been carved. Also, read about the statue of Kefu.
    Surprised that you can not obtain hydrated lime at a building material supplier. Lime is used (and recommended in Australia) to mix with cement and sand for mortar to lay bricks. The lime makes the mix more workable. Quicklime as someone commented is used for stabilising soils which are high in clay. particularly for roads, airfields etc (Cement is better for stabilising sandy soils) Contractors get the quicklime from lime producers. You should be able to ask contractors for a sample. Quicklime is also use in municiple water treatment plants and you should be able to get a sample (a couple of Kgs there)
    However, the Egyptians used lime to make NaOH and KOH. If you want to try making geopolymer yourself you can readily buy caustic soda in a hardware. Many people know that is cheaper than Draino (same material at three times the price) for clearing drain pipes from kitchen sinks.
    In the past one could buy geopolymer kits from the institute but it appears they now only sell information & books and list some supply businesses here

  24. Zeke says:

    “Nice to know. I’m likely to hit up a local “pottery supply shop” first. I really don’t like mail order. If things are not what you expected, it’s just a pain…Then again, I buy stuff mail order sometimes anyway…” Chief

    I thought it would be easier to get as much as I wanted from a supply store, but I ended up ordering from Ward’s and it is a good co. if you can use a box of it for smaller experiments.

    “BTW, love the comic strip! I did recognize the “well, don’t have that, try this” process as a, um, quirk of mine ;-) Mostly it works. Sometimes you get surprises. A few of them are even nice surprises…”

    That was more linked for Mrs. Smith than for you. (: And I do appreciate what you are doing with the liquid rock.

    Plus we have some great opportunities, such as the Geopolymer Camp from LGs link. Any takers? This Egyptian Faiaence paper is terrific.

    I have found the precise control of temperature used by Etruscans as well in some of their work. I sometimes suspect that some ancients were generating electricity, or at least using a form of electrolysis. The Roman Empire stamped it out.

  25. Jason Calley says:

    @ E.M. If you want to make your own lye, the old “Foxfire” series of books gives detailed instructions on lye making from wood ashes. (The Foxfire books may be available online as free downloads.) Another possibility is making lye by electrolysis of a salt solution. Plain old NaCl in water with two electrodes and DC current. The chlorine gas bubbles off, but the newly formed sodium goes immediately back into solution, so you end up with a NaOH solution. Use the liquid, or evaporate it down to a solid. You might even be able to start with a solution of table salt and calcium chloride (CaCl2). Calcium chloride is available in bags as a de-icer and also as an additive to swimming pools to decrease concrete erosion. With NaCl and CaCl2 both in the starting solution, you could electrolyze and go straight to a water solution that already had both Na ions and Ca ions.

  26. Graeme No.3 says:

    Natron is a natural mix of sodium carbonate and bicarbonate (roughly 5:1). It was available in ancient Egypt by scraping it up. No need to roast it, as it slowly reverts on storage.

    Wood gives about 1% ash, which can be extracted with water to produce sodium and potassium hydroxide. Used in medieval Germany for ‘forest glass’ etc. Can’t see much point unless you have a large supply of ashes.

    Sodium hydroxide seems to act as an activator by ‘etching’ the surface to silicate – sodium salt.
    Sodium acts to de-polymerise silicate chains e.g. adding it to water glass will make the resulting mix lower in viscosity.

    Slaked lime is calcium hydroxide as distinct from lime which is calcium oxide. It is slightly safer, esp. when adding it to water. A solution of slaked lime will be as alkaline as sodium hydroxide but a poorer activator.

    The reaction is calcium replacing sodium which makes the silicate insoluble. Aluminium salts introduce cross linking and improve strength. Bear in mind that high alumina cements were popular until it was discovered that they were prone to catastrophic failure when stressed in high humidity (e.g. roof of covered swimming pool collapsing without warning). Phosphates and borates also cross link e.g. borate in glasses esp. pyrex.

    Recommend starting with a slurry of sodium hydroxide and solid fillers. Waterglass would supply a lot of soluble silica and add strength but not be stable on storage. Adding lime slurry should give a fast setting and fairly strong mix. Good luck.

  27. Jay says:

    The acid strength chart seems to have an error.
    It lists pH=0 with hydroflouric acid. HF, though very nasty (I work with 49% HF) and is the most dangerous common acid to work with, it is not a “strong” acid, meaning it does not completely dissociate. It dissociates a few percent at normal concentrations. The extreme damage is because the fluoride ion penetrates and combines with calcium in the body, causing painful destruction that can go systemic and become fatal.

    Sulfuric acid would be a better example or pH=0, of concentrated HCL, HNO3 etc.
    That first proton on sulfuric comes off 100% in aqueous solutions, like nitric and HCl.

  28. Jason Calley says:

    @ Graeme No.3 “Phosphates and borates also cross link e.g. borate in glasses esp. pyrex.”

    Graeme, I am grateful that you know more chemistry than I do!

    So I can use Twenty Mule Team Borax (sodium borate) in place of aluminum? Or maybe I can use a really strong solution of trisodium phosphate (pH somewhere around 12?) to both dissolve the SiO2 and to also supply the phosphate to replace the aluminum. Or maybe just buy some pickling alum (potassium aluminum sulfate).

    Do you think this would work? Mix trisodium phosphate with diatomaceous earth. Let sit for a while or heat to dissolve the SiO2. Add sand, rock or fillers. Add lime slurry. The calcium from the lime kicks out the sodium and the phosphorous cross links the chains. No clay needed.

    Am I understanding this correctly?

    Oh, one last thought… I have read that when the Great Pyramid was first opened that the interior was heavily encrusted with salt. Of course there are a lot of types of salt. My guess is that the salt was probably sodium bicarbonate, not sodium chloride. Does anyone have some insight into this?

  29. Graeme No.3 says:

    there is another factor operating but I thought it best not to complicate matters.
    Sodium metasilicate is used is used in industrial cleaners because it doesn’t attack aluminium and very little effect on zinc alloys. Borax also has the same lack of dissolving power at a lower pH.
    So borax would probably not dissolve enough silica from diatomaceous earth to be practical. Trisodium phosphate is also a lower pH in solution that sodium carbonate (natron) let alone sodium hydroxide. You need some dissolution/reaction at the solid surface to get the necessary bond to the matrix.

    You could try your method but I think you would get 2 effects offsetting each other. The calcium in the lime is likely to react with the phosphate preferentially and not bond (nor displace the sodium) from the solid surface. That would leave the solids surrounded by sodium hydroxide which would collect the water and you’d get far less strength than you want. The other thing I didn’t think to mention is that phosphorus glasses tend to be soft and lower melting point.

    No, you don’t need clay as such, but it is more easily attacked and gives you some of the right species. Besides it is cheap and also thickens up the solution leading to less settling of the solid fillers. That is one of the major uses of bentonite clays (the other as ‘waterproofing’ as a dry coat will swell in contact with water closing off any gaps in the surface below).

    The comment on high alumina cements was just a cautionary tale. Yes, several enclosed swimming pools did collapse without warning and others had to be demolished, but those cements worked (and are still working) outdoors in lower humidity areas. They were originally popular because they developed high strength quickly.

  30. p.g.sharrow says:

    A other source of very high silica content that might have been used is the ash of water loving plants. Rice straw, rushes. etc
    @Graeme No.3 Thank you for your contributions to our knowledge base. I can see a possible use of Rice straw and rice straw ash, hardwood ash, my bentonite rich clay/volcanic ash subsoil and some masonry lime to make a pottery / brick kiln. I know that my clay makes good hard bricks at 1700F but shrinks about 10%. A mix of the subsoil, lime and portland cement with sand makes an excellent mortar mix for stonework, very “fat” and really sticks to the stones. Ages very nicely with little erosion and no cracking or separation from the stones. One drawback! once built the stone work is permanent. Very difficult to break up the work and remove the old mortar to salvage the stones. pg

  31. CompuGator says:

    I’m mystified that someone living more-or-less in Orlando would believe that he needs to guzzle gasoline out to either of the state’s coasts to find sand for a home approximation to a materials-science recipe: The basic so-called soil here in Orlando is gray sand. Its chemical composition? Aside from assuming that it’s limestone-intensive, I readily confess that I haven’t another clue (but the Institute of Food & Agricultural Sciences (IFAS) Web-site likely has details)[*].

    The seemingly plausible alternative of shovelling pails of sand from salt-water beaches gathers an aggregate that (if I recall correctly) can’t practically be washed enough by amateurs to eliminate its substantial disadvantage: The ability of whatever sea-salt remains, to (re)crystalize and ruin the structural integrity of whatever cement|concrete|mortar it was mixed into.[*] Seems to me that that was a major problem that required yet another rebuilding of the nowadays-nominally-Catholic cathedral in St. Augustine (i.e.: the original Catholic diocese in Florida).

    ACE Hardware, which acquired many of the mom&pop hardware stores around metro Orlando, sells “Rooto” brand “100% cautic soda lye” pellets, altho’ it strikes me as seriously overpriced at nearly $10 for a 1-lb. plastic jar. If you’re precise enough to request “ordinary sodium hydroxide” (as I did not too many months ago), expect 20-something clerks to give you a unremedially blank look.

    Decades ago, there was a widespread aquatic-plant eradication program here, targeted at water hyacinths (being quite pretty, but easily able to take over the entire water surface of a lake if dumped from someone’s fashionable pond as the now-unwanted trend from last year)[#]. It relied on pouring copper sulfate from small motorboats into lakes, so that chemical might be more readily available in central Florida without any interrogation than in many other places.

    Note*: See Fla. State Geological Survey, e.g.: “Sand and gravel deposits ofFlorida[:] Orange County” (p. 103): . No need to waste time looking on-line for the source of sand described as the “county road material pit 2_1/2 miles south of Orlando, near the Dixie Highway and Holden Avenue”. It (almost certainly) no longer exists: Altho’ Holden Ave. certainly still does, the intersection identified is one along the perennial urban-renewal strip of modern U.S. Hwy. 441 that’s poetically named South Orange Blossom Trail (which did indeed once have orange groves and their fragrant blossoms–but in decades increasingly past). “Scrub sand” is not a reference to an industrial application for the material, but instead, like the native-bird species commonly known as the”scrub jay”, identifies the (type of) ecosystem in which it’s found.

    Note**: Be that as it may, I did bring a jar of sand from the famous|notorious Monastery Beach of Carmel (Monterey Co., Calif., whose official designation is “Carmel River State Beach, South Unit”, poetic, eh?), back to Florida for sentimental ceremonial purposes.

    Note #: That was before we’d been exposed to the diabolical survival & propagation strategies of Hydrilla, which looks very similar to Elodea.

    General note: What the h*** is with your “Well? Say something!” comments-submission window being only 3 text-lines high? I suppose that could be a really effective ruse from any blogger who’s determined to discourage comments. But I’d gotten the impression that dialogue wasn’t something you were trying to suppress

  32. E.M.Smith says:

    Finally got around to doing the first round of experiments. Hardest part was collecting what I *thought* would be the most important materials. I did 6 different mixes. Most with some combination of Clay (cat litter), Lime (‘pickling lime’ from Walmart canning department), Limestone / Shells (from some ‘chicken grit’ from Tractor Supply), and Diatomaceous Earth or D.E. from the bug spray department of Lowes. As a smaller effort, I picked up some Washing Soda (aka Na2CO3 or Sodium Carbonate or Natron) at Walmart.

    Well, to my surprise, the D.E. / Clay / Lime mix was the LEAST effective. Those that worked best had added Natron. Even the CaCO3 based mixes where I’d expected Lime to matter more.

    WAY to my surprise (as I thought the CaO / Natron reaction to yield lye NaOH to cause a more effective reaction; turns out that the mix that did the most the fastest, and set up the hardest, was a simple mix of:

    Clay, D.E., Natron. In about equal parts.

    Now I’ve done NO measuring for proper ratio based on any particular theory. The “bloom” forming on the top of that mix speaks to me of way too much Natron. So it likely can be made much stronger / better. But my goal was to re-create what might have been the events that lead the Egyptians to discover this process.

    Now it makes sense.

    They had lots of Natron. It was used in embalming, for example. So lots to dispose. Putting it on a spot of clay dump or some clay / sand mix would make for a natural experiment. The D.E. is basically SiO2 so any silicon sand would be a similar chemical reaction.

    No exotic chemical processes needed. No particular super high temp process to form exotic reagents. No exotic mix of volcanic stuff and ‘whatever’.

    OK, I’m going to write it up and make a new posting out of the results; but for now just thought that a bit of a “heads up” early peek was a good idea. No need to hunt down lye or caustic lime.

    This weekend, I hope to try making some kind of “dish” out of local sand, or some silicate sand from the hardware store, a bit of cat litter, and some washing soda. It ought to work… Also I’ll be trying a 10% Natron mix to see if lower concentration still works OK.

    On the lime / natron front, I’ll be trying a lower concentration of both (about 5% to 10% of each) with some clay that’s a bit more ground up. As a ‘first cut’ I just used the kitty litter in the pea gravel sized bits in which it came. The one that ‘worked the best’ had a bit more water than a couple fo the others and the change of grain size may have mattered. So I’m going to redo some of the others with more of a clay powder than clay granules.

    What surprised me the most, though, was that the D.E. / Lime / Clay mix was the LEAST effective. It is still about the consistency of hard pudding… and this is a day later.

    Given that ‘ultimate hardness’ for some mixes has been stated as taking a few weeks, the ‘almost soft stone’ hardness some of these reached in an hour or two promises a pretty usable end product once ‘tuned up’.

    At this point, one of my major lines of exploration will be making small bricks out of sand and natron with maybe a bit of clay. IF I can make such a brick that will stand up to modest water; that’s kind of a big deal. A whole lot of the world lives with unfired mud bricks. Even just a ‘somewhat more durable’ brick would mean far less rebuilding after the rains. All it seems to take is some Na2CO3 (or even sodium BI-carbonate that can be converted in a normal home oven to sodium carbonate) and some clay and silicate materials.


    I just unwrapped 2 of the samples from their paper cups.

    The D.E. / Clay / Natron one shows significant excess natron. A gentle water rinse showed a slippery alkali water on the hands. It is not yet water proof. (Though more water resistant than just clay). I think more sand / solids will be an improvement. Also, the clay does not react inside larger bits. Powdering the clay will help.

    The 3 x Clay / D.E. / Natron shows significantly more unreacted or under reacted clay chunks. Some of the top bits are very easily washed to slippery eroding clay patches. The bottom shows some D.E. excess around the outer edges and the bottom is harder.

    Overall, better mixing of the clay / natron matters along with more silicate content. Probably time to get closer to the recommended ratios in the papers above.

    I’ve made up a roughly 80% clay / 10% D.E. mix and added excess water until it was a slurry (clay bits breaking up mostly). Then stirred in about 10% natron. That cup is set aside and is already setting up. Tomorrow I’ll be trying something similar with added sand.

    Mostly this update is just pointing out that the hardness seen in the cup is not the same as what happens when you dampen the stuff. At that point, any non-reacted but hardened bits that are still water soluble make their presence known… It is still very promising, but points to the need for better technique / mix / reactant choice to make a fully waterproof product.

  33. E.M.Smith says:


    I linked to them (featured them?) in the first article, linked from here… Didn’t see the need to do it again…

    The local hardware stores have largely gone to pre-mixed products. Overall, most simple materials have gone out of use at retail. I can likely get the basic materials from construction wholesalers, but they don’t sell to Joe Public. (Or I need to find a more remote / primitive retail operation…)


    I’m leaving temp control for last. Perhaps a mistake… Part of my intent is to “learn how discovery was made” by doing it sloppy and seeing what ‘accidentally’ works easiest as the most likely first learned method.

    Per ancient electricity: Somewhere or other I’ve posted on it… but there’s a theory that the Lighthouse of Alexandria had a thermoelectric generator in the base and an arc light in the top. It would explain things like the large wood consumed for the fire while hauling that much wood up to a tower top doesn’t work well ;-) They also had all the needed materials. Bimetal thermocouples are easy to make. Carbon arcs are easy. Fire is easy…

    @Jason Calley:

    Good ideas… though I’m looking for a lazy solution ;-) (Actually, it is a time budget issue…)

    I’ll go with DIY if I must, but would rather throw money at it. Or just get some wood ashes and add them directly to the ‘mix’. They ought to work… and it would be a likely thing ancients would have done. Toss ‘waste’ ashes into a pile with some used natron from an embalming and it sits on a sand / clay base. A light rain… wait for it… then some guy digs up a layer of unexpected new solids…

    @Graeme No.3:

    Yes, familiar with the chemistry. The point to using ashes would be to see if the ancients might have discovered things in that way (as they had a lot more ashes…)

    I’m trying to avoid using water glass as it doesn’t impress me as a ‘likely used by the ancients’ kind of thing… Just not likely to form by itself around a camp fire or under a pottery kiln… but I’ll go there if I must.


    Resources and materials are where they are. You must go to them (or someone else must go to them). It’s always nice to know where there is real silicate sand. After all, I sometimes go to Tampa for a Lightning (NHL) game, so it’s not like I’m going there just for sand!

    With that said, I’m eying the sand by the back fence for my first tests. As I’m not yet familiar with Florida geology in detail, I don’t know where the sands are silicate vs carbonate vs…

    With THAT said: IF I need a known silicate sand, I’m most likely to hit the hardware store for a bag so labeled ;-)

    No significant (added) guzzling involved…

    Thanks for the pointer on ACE and lye… will be stopping there in the next day or two…

    As per the size of the comment window: It grows with use… but I have zero control over it. On some browsers / systems (like my tablet) it’s a royal pain as it sometimes doesn’t grown and the typing goes off the bottom into invisible-land… So ask WordPress…

    Easy way to test sand type is put some vinegar on it. Fizz means carbonate… zero fizz means likely just silicates.

    At any rate, I have to get up in 5 hours and go to work, so more must wait for tomorrow…

    I also have a box of Boraxo for some ill defined future experiments.

    BTW, had only I read your description of why sodium matters to etch and soften I’d have understood better what was happening in the Natron based reactions a bit better…


    Unfortunately, a blogger is at the mercy of what is available for free use on the internet… erros and all.

    @Jason Calley:

    Interesting phosphate ideas… TSP is available as a cleaner…

    @P.G. Sharrow:

    Nice practical perspective / points.

    One thing that surprised me so far is how fast things become thick / solid. So far, this technique is not one for long working time. Probably some kind of tuning will fix that…

  34. Sera says:

    “Given that ‘ultimate hardness’ for some mixes has been stated as taking a few weeks, the ‘almost soft stone’ hardness some of these reached in an hour or two promises a pretty usable end product once ‘tuned up’.”

    That would be preferencial, right? I would be easier to ‘final shape’ or ‘work’ with soft tools before it set too hard. Also, what kind of water would the Egyptians have used? Well water, Nile water, rain water or salt water?

  35. Sera says:

    Oops- forgot the link…

    The aquifer is largely composed of hard ferruginous sandstone with great shale and clay intercalation, having a thickness that ranges between 140-230 meters. Groundwater type varies from fresh to slightly brackish (salinity ranges from 240-1300 ppm). The ion dominance ordering shows that sodium cation is most commonly predominating over calcium and magnesium – whereas chloride is predominant over sulfate and bicarbonate. The groundwater is of meteoric origin[3] (the term meteoric water refers to water that originated as precipitation; most groundwater is meteoric in origin). High concentrations of sodium, chloride, and sulfates reflect the leaching and dissolution processes of gypsiferous shales and clay, in addition to a lengthy duration of water residence.

    That’s what I was thinking, too!

  36. p.g.sharrow says:

    Let me see; in soils, sand, even the finest dust is made up of chunks of rock, has no particular charge, generally wets easily and gives up water readily. Clay is a chemical structure ( metal oxides) that has strong static charge and has a platelet structure ( kind of like graphite) often hard to wet and holds water tightly. So adding a carbonate that easily dissolves would change the static charge, wet the clay and put the more soluble oxides into solution. Clays are mostly aluminum oxide, calcium oxide, magnesium oxide, phosphorus oxide, sodium oxide, etc. Lime is just hard clay stone that has been ground. In the creation of mortar mix Sand is the filler to make the mix stiff and stable. Portland Cement is used to speed set up and be water resistant. Lime slows the setup and adds to the cement values. Clay makes the mix sticky and “fat” that is, easy to shape, but it generally makes the mortar hygroscopic and it weathers out.

    In rammed earth and clay bricks, about 20% clay and 80% sand is mixed and then rammed to eliminate air and physical structure. The wet clay glues the sand together into a ridged structure and then drys out over time. The platelet structure is little changed and water can invade, swell the clay and destroy the structure. Adding an additional salt to the clay will change the static charge on the clay platelets and the broken chemical bonds caused will be able to crosslink the clay platelets as the mix cures.and make the structure resistant to water damage. This is the same general thing that Portland Cement does by using burned Limestone (calcium and magnesium claystone) burned shale or slag ( more oxides) and then adding water to mobilize the oxides for crosslinking as it cures. A critical thing is the cure! Full strength of Portland Cement concrete takes 30 days of being wet! The cure is stopped at dry out and will not resume with more water later. I would expect the mixes you are working on will take some time to fully cure. Also sometimes the water in the mix adds strength that will be lost when it completely drys out! It took generations for the Egyptians to get it right and they did not share the technology. the GrecioRomans created their own mix with different materials. Portland Cement requires huge amounts of energy in it’s creation, not something that the Egyptians and Romans had in great abundance.

    In fired clay the heating sinters the clay oxides into glass that wets the sand and glues it together. Too much clay and the fired structure shrinks too much. Too much sand and the structure will not be hard enough. pg

  37. Jason Calley says:

    @ E.M. “I’m trying to avoid using water glass as it doesn’t impress me as a ‘likely used by the ancients’ kind of thing… ”

    Barring some amazing turn around, I would advise not to waste much effort on the water glass idea. I have been trying some mixtures with it and have not had much luck. Like you, I was trying for some quick and dirty combinations just to try to get a grip on the chemistry and proportions involved. I figured that if something set up OK, then I could try variations. Here is what I did: I had an old can of block sealer (K&K Block Sealer) that is mostly water glass (though with some unspecified metallic compounds that seemed to have mostly settled out). I had some D.E., and some regular garden lime (a mixture of calcium oxides, calcium carbonate, and who knows). I did not get any clay, but figured that I probably didn’t need more silicon for initial mixtures since I had the sodium silicates and the D.E. for any silicon needs. I thought I ought to get some aluminum into the mix for cross-linking, so I bought some Clabber Girl Baking Powder, which contains aluminum phosphates. (According to Davidovitz’s book he has found some phosphates added into Egyptian stone samples, so hey, aluminum phosphate sounded promising.

    All measurements were volumetric. First mix a simple 1 part lime, 1/2 part water glass. Result — sloppy mixture, no hardening. Next, 2 parts lime, 1/2 part water glass. Result — a firm, putty like mixture immediately, a small additional hardening over the next three days but not suitable for bricks. Next, 1 part lime, 1 part D.E., 1/2 part water glass. Result — a firm, packed earth texture immediately, slight hardening over next three days, but crumbled when pressure applied, not suitable for bricks. Next, 1 part lime, 1 part D.E., 1/2 part baking powder, 1/2 part water glass. Result, immediate (like instantly) formed small hard pebbles as I attempted to mix in water glass. I broke up pebbles as much as possible and added another 1/2 part D.E. Mixture still too pebbly to stir well, so I added 1 part plain water and continued to mix. After much mixing I finally got a mix much like conventional wet cement, but it did not harden over next three days.

    So what do I think is going on? What I think (though I may be wrong) is this; when using water glass, the silicon is already dissolved. In the presence of Ca and Al the Si ion immediately links up, even before you get a chance to mix the water glass properly. You get pebbles, but not a smooth mix. When you use natron and lime, the water is mixed in well, but the silicon is only dissolved over a period of hours or days. This gives a structure where the SiCaAl is mixed throughout the sample and the bonds hold everything into one matrix, not into pebbles. When I broke up my pebbles and mixed everything together, the reaction was essentially already finished and all I got was a sloppy mixture from broken bits and water.

    Think I am going to have to try the natron route — and maybe check with a masonry supplier to see if plain old slaked lime is available in bigger bags. Or maybe try sodium hydroxide.

  38. Jason Calley says:

    Typo! “I broke up pebbles as much as possible and added another 1/2 part D.E.” should read “I broke up pebbles as much as possible and added another 1/2 part water glass.”

  39. Jason Calley says:

    Sigh…another typo. (Sorry, but I am multi-tasking at work right now and my juggling skills are not what they used to be.)
    “and maybe check with a masonry supplier to see if plain old slaked lime is available in bigger bags” should read “and maybe check with a masonry supplier to see if plain old UNSLAKED lime is available in bigger bags.”

  40. p.g.sharrow says:

    @Jason! start with clay and sand to get a workable mixture. As you work it you will find that the mixture gets”fat” ( will stand on it’s own), then add lime. You will find “slaked” is “hot” will make your mix stiff and “fluffy” and will set up like cement. Raw ground lime will make your mix liquid and it will set very slowly, over years! this does make the mortar self healing in wet weather. I haven’t used salts in the mix but clean CLAY ( NO ORGANICS ) is the key in any soil cement system. I built my dugout greenhouse with soil cement mixes. Used 20% masonry lime/Portland cement to my subsoil 80% that is about half clay and half volcanic ash for the best results. I used a concrete mixer with stucco blades and mixed to a just pourable consistency. After an hour or so you could work it vertically like modeling clay. Remember! no organics, pg

  41. p.g.sharrow says:

    Further note, My subsoil clay is somewhat Benoite like, That it is, high in aluminum oxides and low in salts as it evolved in a heavy rain fall area and originated in an old lahar deposit. Hence volcanic ash and clay mix. pg

  42. Johnboy says:

    I have been experimenting with alkali activated cements for some time now and found that they can dissolve in water but by adding a small amount of zinc oxide they become insoluble.Hope this helps.

  43. CompuGator says:

    On 28 February 2014 at 10:26 pm, p.g.sharrow said:

    I haven’t used salts in the mix but clean CLAY (NO ORGANICS) is the key in any soil cement system. [….] Used 20% masonry lime/Portland cement to my subsoil 80% that is about half clay and half volcanic ash for the best results. I used a concrete mixer with stucco blades and mixed to a just pourable consistency. After an hour or so you could work it vertically like modeling clay. Remember! no organics

    From context, I assume your “no organics” exhortation refers to particles of previously–or still–living plant matter. How does that relate to the importance of straw in Biblical brickmaking [Ex. 5:6–19]?Or are you using the word as in ‘organic chemistry’, referring to carbon compounds (in the sense of contamination by petroleum products)?Won’t both be an issue if wood ash is added to the mix to approximate postulated ancient ingredients? Or was the ash intended as a raw material from which to separately leach a liquid ingredient?Either might be an issue with the source of local silicon that I intended to recommend: Sand from sand-bars or nearshore bottoms of those verrry few fresh-water lakes in & around Orlando that have de facto public access [@]. Right now, there are lots of freshly fallen tree leaves, notably from oaks, and many are likely washing into storm drains in this region, which would add to whatever aquatic-plant material is already there. Worse for inland “fun in the sun”, many lakes are the ultimate destination for roadway run-off, which includes petroleum products leaked from vehicles, flushed by rain into storm-drains [*]. Could the suitability of such impure sand be improved by heating some manageable amount in a home oven (e.g.: while preheating), or over a home grill (e.g.: while waiting for lit charcoal to be ready for grilling)?I suppose you’ve already identified all your coworkers who not only have fireplaces, but also used them during what we call “winter” here. You might not have much more time before the ashes disappear in spring cleaning episodes.——-Note @: This is Florida; it ain’t California: Ain’t no “Coastal Act” here–nor a “Lacustrine Act”–to force public access to bodies of water so as to increase low-cost opportunities for recreation. And yes, I am very aware of shameless discriminatory abuses of the California Coastal Act advocated by its bureaucrats in San Francisco.Note *: At least here, unlike, e.g. Monterey Co. (Calif.) and San Francisco Co., our storm-drain (a.k.a. storm-sewer) and foul-sewer (a.k.a. ‘sanitary sewer’) systems are completely separate. In the Calif. counties I identified they’re a combined system. Guess where the foul-sewage is released when “rainy season” rains add a volume of liquid greater than that for which a local combined system was designed?

  44. p.g.sharrow says:

    CompuGator says:
    11 March 2014 at 11:46 pm
    As to “organics” I meant humus rich living organic soils such as you would use for your garden soil. Your best results will come from a “clean” clay & sand mix. If you thoroughly mix your proposed clay or sand material with excess water and let stand in a jar. sand will settle first and then the clay. Organics will tend to float or stay in suspension. The organics will cause weak cementing. Ash has had the organics burnt out and will help in the cementing. The sand type will add or detract to the finished product strength depending on its’ own strength. Quartz sand, SiO2, is generally used but any clean sand will do.The sand type will add or detract to the finished product strength depending on its’ own strength.The clay chemistry and additives are the cementing agent and the chemistry involved in it will be the most important factor in the finished product quality.
    In unfired clay bricks, straw is sometimes used as a filler and reinforcement. Parts of the Great Walls in China are made of sand, clay, Rice straw, rammed earth and have lasted hundreds of years. Rice straw is very resistant to rotting. Ramming to destroy the clay soil structure, eliminate air pockets and wet the fillers with the cement are most important. You need to use just enough water to facilitate the mix as too much water or too little will give a weak cementing of the filler. It fairly hard to do a really bad job and difficult to do a very good job. After all you are just playing in the mud! 8-) Have fun. pg

  45. Jason Calley says:

    “In unfired clay bricks, straw is sometimes used as a filler and reinforcement.”

    Straw works as a reinforcement for cement too — or at least that is what Bucky Fuller claimed. He did some experiments with (IIRC) straw reinforced cement block used to build a wall. I seem to remember some guys in India using bamboo for reinforcing cement.

    These days, basalt fibers look like a real upcoming product for reinforcement.

  46. 2 by 4 says:

    wow … when i first started reading up on alternatives to cement …. i was pretty excited to find something i thought was usable . . . save a buck or maybe become a little more enterprising … but after reading this entire discussion i realised something …. gone are the days where the average man could live off the land … how did they build houses back then, feed thier families etc …. they utilised what was on the land — for nothing! Lost are the days where this knowledge went from father to son! Can’t imagine a discussion that went…… ” hey bob …. i need some sodium carbonate to build my house … would you mind taking a 3 week horseback ride to go fetch it … heres $8 … and while you there ..pick up some sea sand !!!”

    We got the ability to put a friggin guy on the moon …. but a brick …now thats a tuff one! Unfortunately Portland now has us by the short and curleys!

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