Our process allows the use of a much greater quantity of agricultural waste (chips, weeds, or straw) than other methods.
We keep changing our recipe, experimenting with new ideas, but the following should give you a very sturdy mix:
For purposes of working out formulas, I always start with one bucket of chips/weeds/straw and call that 10 parts,
by volume (we find that formulas measured by volume are much easier to reproduce than formulas by weight).
Our mix is as much as 50% chips, weeds, or straw. We use this material because it is freely available and because
all those pieces strengthen the mix. We use a random mix, striving for some variation in the size of the pieces.
If broken glass is used, that would be part of the 50%.
We used to begin by adding the lime to the chips or weeds, but we have found that it is better to mix up the
lime, clay, sand and cement with water and then add the chips or weeds. We recommend three parts of lime (15%),
a total sand/clay portion of about five parts (25%), and about two parts Portland cement (10%).
There you have it — this mix works very well for us, but you can modify it in many directions.
You can add chipped up paper and cardboard to extend the mix, but it makes it softer and weaker.
You could add more sand and clay, more lime, less cement, broken bottles, floor sweepings,
old clothes (shredded), broken toys . . .
We pour on site in wooden forms, which are removed the following morning, but you could also press bricks and mortar
them together with the above mix, leaving out the chips, weeds, and/or straw.
You can apply a top coat of lime plaster, which is just lime water with fine sand, to smooth out the surface.
For a really smooth inner surface, you could add gypsum to the plaster, along with any natural pigments.
May 7, 2002 —
As I look over what I have written earlier, I see that we still use a very similar mix, although we often use even more chips — up to 2/3 of the total volume.
But I would like to add that, while pouring in forms works just great for foundations, for building walls I would recommend making bricks first. I want to construct a form in three pieces — a piece of plywood with two permanent 2″ x 6″ sides attached, and two sets of parallel 2×6″ dividers, with interlocking notches, to make up a mold for 64 bricks. Fill the mold with agstone, and the next morning you can gently move the fresh bricks to a spot to finish drying/curing. In this way, you can keep up a production of 64 big bricks per day for a building project (if you need more, use multiple molds).