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close this book Handbook for building homes of earth
View the document Table of contents
View the document Foreword
View the document Chapter 1: Introduction - Types of earth houses
View the document Chapter 2: Soils - And what can be done with them
View the document Chapter 3: Stabilization of soils
View the document Chapter 4: Where to build
View the document Chapter 5: Foundations
View the document Chapter 6: Lightweight roofs
View the document Chapter 7: Preparing the soil
View the document Chapter 8: Making adobe blocks
View the document Chapter 9: Making pressed earth blocks
View the document Chapter 10: Making walls with earth blocks
View the document Chapter 11: Making rammed earth walls
View the document Chapter 12: Roofs for earth houses
View the document Chapter 13: Floors
View the document Chapter 14: Surface coatings
View the document Suggested references
Open this folder and view contents Appendix

Chapter 9: Making pressed earth blocks


Figure 49. The various shapes of blocks produced by the Land-crete block making machine allow rigid construction of corners and tees.

ELLSON BLOCKMASTER - The Wilson Blockmaster is a manually-operated block (or brick) making machine manufactured by Wilson Equipments (Pty.) Ltd., 285 Fox Street, Johannesburg, South Africa. The machine operates on a lever system with a constant length of stroke so that the block thickness is always the same. The high lever ratio (500-1) makes a very dense, solid block. Different molds can produce blocks 9x12x4 inches or 6x12x4 inches. Other molds and attachments are available to form interlocking blocks, 4½x9x4 inch bricks or 18x9x4 inch hollow blocks. The manufacturer claims a production rate of 900 to 1100 blocks per 8 hour day with an increased rate up to 1400 to 1500 blocks per day with a semi-automatic loader attached. If the 4½x9x4 inch bricks are made, the rate is approximately doubled since two bricks are made in one operation. Two men would be required to operate the machine and two or three more to prepare the soil.

CINVA-RAM - The CINVA-Ram (Figure 52) was developed by the Inter-American Housing and Planning Center (CINVA) at Bogota, Colombia, in 1952. It is operated by manually applying pressure on a long lever arm. It produces blocks which are 11½x5½x3½ inches (either hollow or solid) and will also produce 11½x5½x1½ inch tiles for roofs or floors. The long lever arm arrangement produces dense, high-quality blocks. The CINVA-Ram is presently distributed by Metalibec Ltda, Apartado Aero 233-NAL 157, Bucaramanga, Columbia, South America, under license from l B. EC. Housing Company, New York, U.S.A. The machine weighs only 140 pounds and is the lightest of the four machines mentioned here. Three men, doing all of the work, including processing, mixing, molding, etc., should make 300 blocks a day. Five workers can make 600 per day by dividing the jobs.

SUMMARY OF BLOCK-MAKING MACHINES - All of the machines discussed above make high quality earth blocks. Each machine certainly has its advantages and disadvantages and certain machines will be available in some areas of the world where others will not. There are probably other good machines that will make good earth blocks, but it is not practical in this manual to discuss all of them. We will use the CINVA-Ram machine to discuss the procedure for making blocks.

BLOCK-MAKING OPERATIONS - A team of five or six men working with one machine achieves the best production. Three men handle the digging and processing, while two men operate the machine and mold the blocks. Another man may be used to stack the blocks for curing.

PLACING SOIL MIX IN MACHINE - With most of the block-making machines (particularly with CINVA-Ram) it is necessary to get the correct amount of soil mix in the machine each time. Fast, simple weighing equipment can be used, but a wood or metal scoop will do almost as well. A scoop for the CINVA-Ram is shown in Figure 53. A worker can scoop into a loose pile of prepared soil mix, scrape off the excess material with a piece of straight wood or sheet metal, and then dump this measured amount directly into the machine. The size of the scoop is determined by the correct amount of mix to make a dense block. Another way is to use only one size scoop but use an adjustable scraper as shown in Figure 53.


Figure 53.

Before each scoop of mix is placed in the CINVA-Ram, a light coat of oil should be brushed on the sides and bottom of the molding box. A mixture of I part engine oil and one part of kerosene is fine. The oil coating keeps the blocks from sticking to the sides of the mold and makes them easier to force out.

The scoop of soil mix is then placed in the oiled mold box. For many soils, a scoopful of loose material will not completely fill the mold box and the cover can be easily closed. Some soils, however, have a tendency to "fluff" when moist (usually. the sandy materials do this) and they must be lightly pressed clown by hand before the mold cover can be closed. It has also been found that many blocks are not compressed tightly at the corners and these corners will later chip or break off during handling. This does not affect the overall strength of the block but can spoil the looks of the wall later on. To avoid this problem, loose mix in the corners can be pressed down tightly by hand or a little excess soil mix can be placed in each of the corners.

PRESSING THE BLOCKS - The worker who fills the mold box slides the cover on. His partner applies the pressure on the lever. This is a most important part of the operation and requires practice to do well. The CINVA-Ram was developed so that as little as 70 pounds of force applied to the end of the lever produces a block dense enough to be satisfactory. However, it has been proved that denser blocks are much stronger and more weather-resistant. So, it is recommended that at least 130 pounds of force be applied to the lever arm; that is, a man weighing about 130 pounds should be able to apply all his weight to bring the lever down to a level position.

A good block depends on the correct amount of soil in the mold box. If the lever arm can be pushed to the level position without pressing hard, then not enough soil has been placed in the mold and the block will not be dense If too much soil has been placed in the mold, then the lever arm cannot be brought down to the level position, even with considerable force. The block produced in an overfilled mold still will not be dense enough. The builder can judge when he has the correct amount of mix in the box: He will feel the greatest force when the end of the lever lacks about one foot from being level.

If weighing equipment is available, you should determine the density of your blocks by measuring their weight and volume. The best blocks are the heaviest or most dense ones.

EJECTING BLOCKS - In the CINVA-Ram, blocks are pressed out of the mold by lifting the lever arm and swinging it to the other side of the mold box. After extruding, the block should be transferred to a suitable place for curing. If the top of the block bows or cracks during this extruding process, the soil mix was probably too wet. These blocks will be weak and should not be used. Newly-made soil blocks containing clay can be handled with little fear of breaking. New sandy blocks may crumble when handled, so they should be moved on a wood or metal piece called a pallet. Some fresh blocks must remain on pallets until they are strong enough to be moved. It may be necessary to have enough pallets on hand to handle an entire day's production of blocks. The only way to know whether pallets are required is to make blocks and see how they hold together when they come out of the machine.


Figure 57.

CURING BLOCKS - While curing, blocks should be stored in a place where they will not be disturbed and close to where they will be used.

Curing is completed when the water used for molding is dried out. They will dry out faster in the sun. If the area received a lot of rain, dry them out under a covering or cheap shed as shown in Figure 57. If the roof of the house was built first, dry them under the roof.

A wet cure period is necessary for stabilized blocks to gain strength, particularly if they contain cementing type stabilizers. (See Chapter 2.) During the wet-curing period, blocks should be stood on end and covered with wet sacking, leaves, or other material as shown in Figure 58 so they can be kept moist. After curing, the covering is removed and the blocks are stacked while they dry.


Figure 58.

Some builders do not wait until the blocks are completely dry before laying them in the wall. This does no harm as long as the blocks do not crack when being laid and do not shrink later. But, let them cure for at least a week before using; the longer the better.

CHECKING QUALITY OF BLOCKS - When a large number of blocks is being made, a few bad ones are bound to turn up. Sometimes, even a whole batch of blocks will be of poor quality because somebody did something wrong. Mistakes happen, and the builder can guard against them by performing occasional control tests. The type and number of tests that should be performed depend on the size of the job and type of construction. For pressed earth blocks the following tests are recommended:

1. The moisture content of each separate mix should be checked before blocks are molded. If the mixes are small, you can check moisture by making a ball of the moist mix as described in Chapter 2 and dropping it on a hard surface. For large mixes try to use the more exact tests for moisture described in Appendix B. Use soil samples weighing 1 to 2 pounds.

2. Spray tests should be performed occasionally to see if the resistance to weathering is as good as expected. These tests should be performed on cured blocks using the procedure described in Chapter 2. If the job is just starting then 2 or 3 (or even more) bricks out of the first 100 bricks should be checked. Later it is sufficient to check one brick out of every 150-200 bricks made.

3. The strength of the block should also be checked often to make sure that the block will be as strong as expected. These tests should be performed on cured blocks using the procedures given in Chapter 2 or Appendix A. The number of tats that should be performed is the same as given above for the spray tests.

4. Absorption tests can be easily performed on cured blocks using the procedure given in Chapter 2. Make an absorption tat each time you do a spray test.

5. Density tests to determine whether your blocks are being pressed enough should be done if weighing equipment is available. Remember that the heaviest blocks are the best ones.

If the blocks do not pass these control tests, block-making should be stopped immediately until the trouble is located.