Pressed Earth Blocks: Make 'Em Yourself!

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WE DIDN'T NEED MANY TOOLS

The tools we used in the construction of our wall/ fence Included a pick, shovel, hoe, sprinkling can, sifting frame (a piece of 1/4"-mesh screen mounted on a 4' X 4' frame made of two-by-fours), and-most important of all-a CINVA Ram.

The CINVA Ram is nothing more than a manually operated press that converts ordinary earth (along with a small amount of cement) into substantial 4" X 6" X 12" blocks. ("CINVA" is the Spanish acronym for the Inter-American Housing and Planning Center of Bogota, Colombia ... and Ram comes from the name of Paul Ramirez, the Chilean engineer who Invented the brickmaking device.) We bought ours from the Schrader Bellows Division of Scovill Manufacturing Company (P.O. Box 631, Akron, Ohio 44309) for $250. (At the time, $250 seemed like a lot of money .. . but we've more than earned back that Investment, considering the thousands of 32Qapiece construction blocks we haven't had to buy since we purchased the simple machine.)

Just about any kind of earth can be used in the CINVA Ram to make blocks, as long as the soil contains a little clay and sand. (The dirt should be completely free of !eaves, twigs, and other organic material, however.! To find out whether your soil is suitable for blockmaking, all you have to do is f11 fill a wide-mouthed glass jar half full of pre-sifted (to remove large contaminants) earth, 121 add an equal amount of water, 131 cover the jar and shake it vigorously for a few minutes, then 141 allow the container to stand undisturbed for 30 minutes. At the end of this period, the soil will have separated into three layers: sand on the bottom, clay in the middle, and silt on top. The best blocks are made from a mixture of about 75% sand, 15 to 20% clay, and 5 to 10% silt. If your soil varies too far from this ideal, it's a simple matter to add enough supplemental sand, clay, or silt to even the formula out.

Next, determine how much cement you'll have to add to the earth-to make your blocks "set up" right-by performing a "shrinkage test". First construct a wooden box-open at each end-with inside dimensions of 1-1 / 2" X 1-1 I2" X 24". Then grease the interior of the container-old motor oil is fine and pack it full with moist, presifted earth. Finally, let the box sit for a few days (until the soil has completely dried).

As it dries, the dirt will shrink into a narrow block somewhat smaller-In all dimensions-than the box !t was formed in. What you want to do with the completely cured block is push it down to one end of the container and measure the amount of contraction. Our soil shrunk between 1 / 2" and 1 " in this test, which meant we needed to stabilize every 16 parts of the soil with one part cement. (Had the shrinkage been more than 1 ", we would've needed to use proportionately more "binder".)

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