YOU CAN BUILD WITH SOIL-CEMENT BLOCKS

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We found it convenient to make a stand for our sifting tray to rest on while in use. Three sides of the support's base are walled in solid to keep the sifted soil neatly confined as it falls through the screen on top . . . and the fourth side was left open so that we can shovel the dirt out as we want it.

MAKING THE MIX

Once your soil has been dried and sifted, you can begin to prepare the mix from which your bricks will be pressed.

The amount of portland cement you use will depend upon the composition of the earth you have at hand: Sandy loams must be fortified?by volume?with from 4.75 to 9.10% cement, desert-like silty dirts need 8.35 to 12.5% of the stabilizer, and clayey soils require 12.5 to 15.4% of the binder. More than 15.4% cement is not recommended.

It's actually rather easy to calculate these proportions. For instance, to get a 10%-cement mix, you'll need to measure out one cubic foot of portland cement for every nine cubic feet of sifted, dry soil. This isn't at all difficult to do if you can scrounge up some buckets or containers?preferably with handles?of known volume to work with.

Thoroughly combine all the dry ingredients: cement, sifted dirt, and special additions?such as sand or clay?that may be needed to "round out" your soil's composition. A cement mixer made this part of the job easier for us . . . but?if you can't obtain one of the machines?you can rake the materials together by hand on any level, hard, and nonabsorbent surface. Just take care to avoid contaminating the mix.

The final ingredient that you'll need to make blocks—water?must be added a little at a time until the damp soil-cement reaches the right consistency. (Here, we used a garden hose with the nozzle adjusted to produce a fine spray.) There are several ways to tell when you should stop adding the liquid. For one thing, if you take a small amount of mix and form it into a ball in your hand, the resulting clod should both hold its shape and not stain your palm. The ball should also pull apart without disintegrating, and should?when dropped from a height of 1.1 meter (43.3 inches)?shatter into a loose material that resembles the original mix.

FROM MIX TO BRICKS

The soil-cement can now be loaded into the CINVA Ram's mold. About the only tricky part of this procedure is filling the box with exactly the right amount of the mixture each time.

With a little experience, you'll be able to tell if the Ram contains as much of the earth?binder mix as it should by the pressure required to depress the machine's long handle. Ideally, you should be able to feel some resistance . . . but it shouldn't be necessary to "fight" the lever down. I can only suggest that you make a number of trial bricks?employing carefully measured amounts of soil?cement?to determine the correct loading volume, then make an appropriately calibrated scoop. (We used a plastic bleach bottle with the bottom cut away, while some friends of ours built a solid little wooden scoop that's easier to handle?and more accurate?than our recycled model.)

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