YOU CAN BUILD WITH SOIL-CEMENT BLOCKS

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THE FIVE BASICS OF BLOCKMAKING

The basic brickmaking process can be broken down into five steps: [1] analysis of the soil, [2] sifting of the earth, [3] preparation of the mix, [4] manufacture of the blocks, and [5] the curing of the bricks.

We'll discuss each of these activities in some detail.

SOIL COMPOSITION

Analysis of the soil that will be transformed into bricks is the first (and probably most complicated) step in the manufacture of pressed-earth blocks. You must know the composition of the dirt you intend to use before you can estimate the amount of cement?and/or missing "native" constituents?that must be added to the final "mix".

All soils are made up of three components: sand, silt, and clay. These components are defined on the basis of particle size (sand being the coarsest of the three and clay the finest).

Somewhat sandy earth seems to make the best CINVA Ram blocks and the optimum soil for the bricks is made up of approximately 75% sand and only 25% silt and clay. (The clay alone should never comprise less than 10% or more than 50% of the total.) A good deal of variation from this ideal is permissible, though. According to the instructions which came with our machine, "Most earth, when reasonably free from vegetable matter, will make good compressed-earth blocks."

You can get a rough idea of the composition of your soil by simply picking up a handful and feeling it. Sand?naturally—has a coarse and gritty texture, while silt has the consistency of flour. Moist clay is smooth to the touch, is somewhat sticky, and will form a ribbon as you compress it between your thumb and forefinger.

To better estimate the percentages of each component: [1] Fill a straight-sided glass jar about one?third full of earth. [2] Add an equal volume of water. [3] Cover the jar and shake vigorously to suspend all the dirt. [4] Finally, allow the slurry to sit undisturbed about 30 minutes or until the soil has settled into three separate layers with the sand at the bottom.

SIFTING

Whatever the consistency of your soil, it must be dried and sieved (to remove large lumps, stones, leaves, and other impurities) before the dirt can be properly mixed with cement and compressed into blocks.

The soil has the proper moisture content for sifting when [1] a handful can be squeezed without water appearing on its surface, and [2] the ball of earth disintegrates without lumps as it's released. Damp soil of this kind can easily be pushed through a quarter-inch screen.

You can construct a sturdy sieve in any of a number of ways. Ours, for example, is simply a piece of hardware cloth mounted on a three-foot-square frame made of 2 X 4 lumber. The important thing is to keep the structure lightweight and small enough to handle easily, because you'll need to dump an accumulation of stones and other material off the screen every now and then.

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