Jane Marie

Jason, thanks for taking the time to re-answer my questions. See attached, I ran across this article and magnesium cement. Excellent properties that bind well with cellulose. The properties seem hard to beat (see quote below). How would geopolymer cements compare?

"Magnesium-based cements commonly achieve compressive strengths of 9,000 to 45,000 psi and tension strength of over 800 psi, many times stronger than that of conventional concrete. Magnesium oxide combined with clays and cellulose form cements that breathe water vapors electro-magnetically, a significant plus. The clay in magnesium oxide balances and enhances the movement of moisture. It never rots because it always expels moisture. Also, unlike Portland cement, MgO cements will not drain the charge out of a car battery left overnight on a floor made with as little as 20% MgO content. MgO cements are completely non-conductive of electricity, as well as heat & cold, and have been used for flooring for radar stations and hospital operating rooms throughout the 20th century."

Jason, I gather you are a chemist? I had a hard time following the dialog, do you mind if we start with the basics and some practical examples of materials?

"A geopolymer is a polymer that uses repeating mineral chains instead of repeating carbon chains. Most often found with a silica alumina bridge to link them. So Silicon and Aluminum have replaced the carbon, however, there are geopolymers that use phosphate and aluminum as well as others some found in nature. Caliche clay being one. "

So would hempcrete or strawcrete be a "geopolymer" ? From what I understand, the hemp plant has high silica content(80-90%) like no other plant that binds to the silica in lime to make hempcrete? Is that true, or is there another chemical bond like with MGO? I found on the internet that wheat straw also has a high silica content of around 60%, others straws and grasses with silica. Straw is more readily available than hemp in the US but, farmers are now growing it, and seems to work but, I'm not sure about this theory of it recurring absorbing CO2 to revert back to rock when it gets wet and the bond getting stronger indefinitely? I wonder if that has every been quantified and proven.

Or am I way off track and these cretes are not in the family of " geopolymers"? If you don't mind, please simplify your answer for the non-chemist

Thank you.

Jason, are you still viewing this thread? Do you mind if I ask some questions?

Thanks for the reply Rick.

See Rammed Earth Pics: The surfaces have some fines(sand, iron oxides) that are not very abrasive & rub right off. I tried linseed oil (bottom of end, brown boiled) it darkens the wall quite a bit, and a water based acrylic concrete sealer not as dark but still unacceptable. Any ideas on a clear sealer that won't darken? The mix is soil, sand, limestone.

When I build a home I'd like to keep the interior wall permeable and breathable. This retaining wall I want to protect from erosion, the elements, so it can have a lower perm or barrier sealer.

I have a rammed earth wall being constructed outside as a retaining wall and inside as a pony wall. First project is coming along great but, wondering how to seal it using a natural eco-friendly material. Envision a live wall with moss or other green vegetation so, would hope the sealant would not preclude cultivating on the surface. Sealant should also have surface hardening efficacy as well as protecting against water erosion. So, specifics: natural, non-toxic, eco-friendly; hardener to create enduring resilience (e.g., heavy objects banging into wall yet integrity maintained); water/moisture seal/protectant; surface amenable to live plants (e.g, moss wall). Any ideas of products that would fulfill these criteria?