Some of this was gleaned from old postings in which I explain how to get free gypsum and the experiments I've conducted with this material.
Houses built before 1980 often have ASBESTOS drywall tape and mud, so don't get your material from houses this old.
Many heating systems which use heated water under the floor prescribe the use of gypsum covering the pipes since it is good at radiating heat and it has a high heat capacity (.26 as compared to .2 for
cob). This material is commonly purchased in bags just like cement and lime are packaged. It costs seven dollars for a 40 pound bag.
Now the free part. Actually it's much better than free! Used a drywall is made of gypsum and depending on where you live can cost anywhere from $100-$200 per ton for disposal. Where I live in Victoria BC I charge $200 per ton for the removal of this material. Find a drywaller and become his disposal guy and make at least $100 per pickup load.
EXPERIMENTS
Using a small children's pool I soaked some of this material and then ran it through a bearcat garden chipper. The resulting paste was somewhat chunky but very easily troweled and there is no reason why this could not replace purchased gypsum. I will use more than 10 tons of this material as soundproofing and as thermal mass adjacent to my
RMH. Houses built before 1980 often have asbestos drywall tape so don't get your material from houses this old.
I ran several strength tests on gypsum which I pulverized in the garden chipper. I made several hockey puck sized
pancakes of this material and allowed them to dry. With some I stripped the paper off and pulverized only the gypsum and then mixed half of this batch with 10% Portland cement and the others I just allowed to dry without additives.
The one with Portland required maybe 20 pounds pressure to break with a twist of the wrist. The one without Portland required less than half as much strength and it crumbled.
Next I ran some gypsum through the chipper paper and all. Again one batch of pancakes was mixed with 10% Portland cement and the other was just allowed to dry. The one with Portland cement and paper was so strong I couldn't break it with my hands. The one with just paper broke with a hard twist of the wrist and was probably twice as strong as the sample with Portland cement but no paper.
So for most purposes drywall can simply be run through a hog with paper attached and a relatively strong and malleable paste results. This product is not sticky enough to use on its own as a finishing plaster but it would certainly work for filling cavities anywhere in a house where you're looking for thermal mass and soundproofing.
Since all paper is covered in gypsum these cakes were fireproof.
Running gypsum through any sort of chopping device while dry is asking for a dust storm and would also wear out your equipment faster. The dampened material made no dust and it ran quieter than when chipping branches. Restricting the outflow allows for a very fine grind but for most purposes you're simply looking for lots of easily spreadable material so the stuff could be run through rather quickly.
IMPORTANT NOTE: although the resulting material looks a lot like
concrete it is highly absorbent and completely unsuited for any exterior application. Even the cakes with 10% Portland cement become soft and breakable when wet.
I've conducted experiments on several other readily available materials and will post a separate
thread concerning the results. I have a pretty good understanding of scientific method and although I'm a mad scientist, I'm only mad at waste and inefficiency
. Thank you: Dale
