The Owner-built Adobe House

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[4] Repeat this procedure with boxes full of soil mixed with 12 ounces (0.4 L.), 10 ounces (0.3 L.), 6 ounces (0.2 L.), and 4 ounces (0.1 L.) of emulsified asphalt. Label each brick as to the amount it contains.

[5] Put these bricks on a cookie sheet and dry in the kitchen oven (200° to 400°F) for several hours. Before removing them all, break one open to make sure they have dried all the way through.

[6] Immerse your test bricks in water for several hours. Bricks with enough emulsified asphalt will not soften along the edges. You want to use no more than the minimum amount of asphalt needed to waterproof your bricks, since too much will weaken them.

Following is a chart that will show you how much emulsified asphalt to use per brick.

As soon as you have determined how much emulsified asphalt to use, go ahead and make a limited number of bricks. When your bricks are tested by a commercial lab, they will also be tested for water absorption, as required by the building department. However, any brick that passes your water test will absorb less than 2.5% moisture by weight. If you own a small scale, you can also make your own moisture test.

It is possible to stabilize your bricks with Portland cement in the ratio of 1 part cement to 12 parts soil. These bricks. while quite strong, are not waterproof and will not meet Uniform Building Code requirements.

Burnt adobe bricks are also used in some areas. These are simply kiln-fired adobe bricks. They are attractive and durable but extremely absorbent, and will flake severely in areas where frost is a problem.

STRENGTH TESTS

Following are two simple tests you can conduct at home to give you a general idea of just how strong your bricks are:

[1] Once your bricks have been cured, try to break one by hand. Twist it with your hand, then put it down and stand on it. If your brick survives this test without breaking, it is probably strong enough to meet minimum requirements.

[2] You can also make a simple compression test using a sample adobe brick and two 2 X 4's nailed together as shown in Fig. 2. Start testing at the distance shown for 250 pounds (113.5 kg.) per square inch (6.45 sq. cm.). If the brick doesn't break, then move out and test for 300 pounds (136.1 kg.) per square inch. If the brick passes this test, it is probably acceptable.

As soon as you have produced a hundred or so bricks, have a commercial test made for compression and for modulus of rupture. I simply took two bricks to the lab and asked them to give me a written report. Then, when I finished my brickmaking, I selected three more bricks at random and had them tested. These written test reports were enough to satisfy the building department requirements.

MAKING YOUR ADOBE MOLDS

You will, of course, need some sort of mold to produce bricks. This can be a single mold or a multiple mold producing two or more bricks . . . the mold can be made of metal, wood, fiberboard, or anything else. In practice, I found a five-brick wooden mold worked best for me (Fig. 3).

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