A few years ago-while reading Ken Kern's good book The Owner-Built Home, I stumbled upon something that made me stand up from my chair: CINVA Ram, a manually operated machine that can transform ordinary earth into Into a sturdy 4 X 6 X 12 inch building brick.

Since I was always looking for cheap construction supplies, I was (to say the least) interested in the idea of ​​turning soil into concrete-like blocks. I admit that I am very skeptical, however, on the cold and humid eastern edge of Washington State, that ordinary garden-style soil—for God's sake—can be used as a construction medium.

However, after reading more information about compacted soil, I learned that its main limitation-susceptibility to moisture attack-can be overcome by adding cement as a "stabilizer" to the raw soil. Well, this is enough to convince me to give it a try. .. So I rode CINVA Ram with some friends and started building my barn, chicken coop, and fireplace made entirely of cement blocks.

Now, two years later, I am happy to report that these structures have successfully passed a very harsh winter and have generally met my highest expectations. Cement soil not only has excellent insulation properties, but also is strong, durable, fireproof, easy to use and very low cost. (My bricks cost me 3 cents for each piece... If I hadn't been forced to buy clay and sand to add to our local silty soil, they wouldn't even cost that much!) In short, cement Soil is everything I think construction materials should have.

If you are wondering, CINVA is an acronym for the Center for Housing and Planning of the Americas in Bogotá, Colombia. .. Ram is named after Paul Ramirez, a Chilean engineer who invented this brick-making equipment in the mid-1950s.

CINVA Ram consists of a box or mold filled with wet cement and a lever-driven piston that compresses the soil binder mixture. Once the mold is loaded with the right amount of material, the operator of the machine will force the long handle down with 70 to 100 pounds of pressure (in turn, apply 40,000 pounds of pressure on the compressed soil). The bricks formed by this procedure are then ejected, placed in a cool place, and allowed to cure for up to three weeks.

Although not technically difficult, using CINVA Ram to make building blocks is a so-called "labor-intensive" operation. Four adults-working on organized assembly lines with the help of mechanized cement mixers-can only produce about 50 4 X 6 X 12 inch bricks per hour. (Because even a small house requires thousands of building blocks, so you can understand why few people try this construction technique alone!)

However, to be fair, and to give the other side of the story: the manufacture of CINVA Ram bricks may require a lot of labor. .. But they are also very sturdy, durable, fireproof, cost little out-of-pocket, and have good insulating properties. In short, if you have more time than money, you want to build using local materials, and you need a durable structure. .. Using CINVA Ram to make a blocky cement-soil mixture may be your answer (just like me).

The basic brick making process can be divided into five steps: [1] soil analysis, [2] soil screening, [3] mixture preparation, [4] block manufacturing, and [5] solidified bricks.

We will discuss each of these activities in detail.

Analyzing the soil that will turn into bricks is the first step (and possibly the most complicated) to make a compaction block. Before estimating the amount of cement and/or missing "natural" components that must be added to the final "mixture", you must know the components of the dirt you intend to use.

All soils are composed of three components: sand, silt and clay. These components are defined in terms of particle size (sand is the coarsest of the three, clay is the finest).

A little sandy soil seems to be the best CINVA Ram block, and the best soil for bricks consists of approximately 75% sand and only 25% silt and clay. (The clay alone should not be less than 10% or more than 50% of the total.) Nevertheless, a big difference from this ideal situation is allowed. According to the instructions attached to our machine, "Most soils can be made into good compaction blocks if they are reasonably free of plant substances."

Just pick up a handful and feel it, and you can get a rough idea of ​​the composition of the soil. Sand-naturally-has a rough and sandy texture, while silt has the consistency of flour. The damp clay is smooth to the touch, a bit sticky, and forms a ribbon when you compress it with your thumb and index finger.

To better estimate the percentage of each ingredient: [1] Fill a straight-sided glass jar with approximately one-third of the soil. [2] Add an equal volume of water. [3] Cover the jar and shake it vigorously to suspend all dirt. [4] Finally, let the mud sit for about 30 minutes, or until the soil has settled into three separate layers with sand at the bottom.

Regardless of the consistency of the soil, it must be dried and sieved (to remove chunks, stones, leaves and other impurities) before the soil and cement can be properly mixed and compressed into blocks.

When [1] can squeeze a handful without water appearing on its surface, the soil has an appropriate moisture content, and [2] the soil ball will decompose without agglomeration when released. This moist soil can easily pass through a quarter-inch screen.

You can construct a strong sieve in many ways. For example, ours is just a piece of hardware cloth, installed on a three-foot square frame made of 2 X 4 lumber. It is important to keep the structure light and small enough to be easy to handle, because you need to dump the piled stones and other materials off the screen from time to time.

We found it convenient to make a stand for our screening tray during use. The three sides of the support base adopt solid walls to keep the sieved soil neatly confined in it when it falls through the top sieve. .. The fourth side is open so that we can shovel off the dirt as we wish.

Once your soil is dry and sieved, you can start preparing the mixture for pressing bricks.

The amount of Portland cement you use depends on the composition of the soil you have on hand: sandy loam must be strengthened with 4.75% to 9.10% cement, desert-like silty soil needs 8.35% to 12.5% ​​stabilizer, and clay soil 12.5% ​​to 15.4% adhesive is required. It is not recommended to use more than 15.4% cement.

Calculating these ratios is actually quite easy. For example, to obtain a 10% cement mixture, you need to measure one cubic foot of Portland cement for every nine cubic feet of sieved dry soil. If you can find some buckets or containers of known capacity, it is best to have a handle, which is not difficult to do.

Thoroughly mix all dry ingredients: cement, sifted soil, and special additives such as sand or clay, which may need to "perfect" the composition of the soil. The cement mixer makes this part of our work easier. .. But-if you can't get one of these machines-you can rake the material together by hand on any high, hard and non-absorbent surface. Take care to avoid contaminating the mixture.

The last ingredient required to make a block—water—must be added a little at a time until the damp cement soil reaches the proper consistency. (Here, we used a garden hose with a nozzle adjusted to produce a fine spray.) There are several ways to tell you when you should stop adding liquid. On the one hand, if you take a small amount of the mixture and form it into a ball in your hand, the resulting clod should retain its shape without soiling your palm. The ball should also be pulled apart without breaking down, and when dropped from a height of 1.1 meters (43.3 inches), it should break into loose material similar to the original mixture.

Now the cement soil can be loaded into the CINVA Ram mold. The only tricky part of this process is filling the box with exactly the right mixture each time.

With a little experience, you can judge whether Ram contains as much soil mixture as possible by the pressure required to press the long handle of the machine. Ideally, you should be able to feel some resistance. .. But there is no need to "knock down" the lever. I can only suggest that you make some test bricks, use carefully measured amounts of cement and soil to determine the correct loading, and then make a properly calibrated spoon. (We used a plastic bleach bottle with the bottom cut off, and some of our friends made a small sturdy wooden spoon, which is easier to handle and more accurate than our recycled model.)

Taking out the new block from the Ram requires a fine touch, because the newly formed block is plastic and fragile. Ram's instructions suggest "put your hands flat on the end of the block, taking care not to damage the corners or edges, and then gently lift the block from the mold box". We were more successful in pressing the palm of the hand flat against the long and narrow side of the brick (as shown in one of the photos attached).

As soon as possible, place the bricks on a flat, non-absorbent surface in a cool environment (a cement board or cement board covered with plastic sheets is ideal) for curing. Make sure to place each block on the edge and separate the bricks far enough so that they don't touch each other. Please note that bare ground-will draw water from the blocks so quickly that they will weaken or even crack. This is not an acceptable surface that can make your blocks age.

If possible, the curing location should be located directly close to Ram, as you will find it difficult to take the newly formed bricks far away. Ken Kern recommends that you erect the roof of the building first in the section on the compact structure of the house built by the owner, so that you can use the protected area below as a curing "yard".

The slower the cement soil blocks dry, the stronger they are. This means you should cover your bricks with plastic during the first four days of their healing. In addition, starting 24 hours after they left Ram, they had to spray the soil cement block thoroughly with the fine spray of a garden hose 3 times a day. The bricks can be piled up on the fourth day, but they will be sprinkled for another eight days. Finally, three weeks after leaving the mold, the block can be used for construction.

The same construction techniques used for concrete blocks can be used for compacted earth bricks. However, before laying cement blocks, it is best to immerse them in water to prevent them from absorbing water (thus weakening it) from the mortar used to hold them together.

As usual, the layers of bricks should be laid in such a way that the vertical seams of a row coincide with the center points of the blocks in the upper layer. In addition, the thickness of the mortar at all joints should not exceed one centimeter (four tenths of an inch).

Because our winters in eastern Washington are cold and wet, we think it is wise to seal our blocks (so that they are always waterproof). To this end, we applied a transparent acrylic masonry sealant on the finished cement-soil wall. Of course, many other paint and plaster finishes can also accomplish this job.

It's sad, but there are not many books on the subject of building with compacted soil blocks. I can recommend a rich text to anyone interested in this structure is the "Handbook of Building a Home on Earth" by L. Wolf Skill, W. Dunlop and B. Callaway. Of course, Ken Kern also dedicated a chapter. Introduced the themes in the house built by the owner.

Otherwise, you are on your own. Just [1] buy CINVA Ram, [2] ask for help from a few friends, and then [3].

So, what if you do live in a part of a country where winters are cold and wet? The soil compaction effect is very good in cold weather or not. Believe me. I know.

Before you start thinking about building a house, barn, or other habitable structure using compacted soil blocks, you should make sure that the cement-soil mixture you use is the best. how? First, four test mixtures were used to make bricks: one containing the largest amount of cement, one containing the least amount, and the other two containing a medium concentration of binder. 'Let the blocks cure for 15 days and then test them in each of the following situations:

Tensile strength: Place a brick on two supports 20 cm (8 inches) apart, and then place the weights one by one in the center of the brick until it breaks. The mixture that produces the strongest lumps is the best.

Hardness: Nails driven with bare hands should penetrate the brick to a depth no more than five centimeters (approximately two inches).

Sound: When struck lightly with a hammer, the bricks should make a metallic sound.

Unit weight: The mixture that produces the block with the largest weight—and therefore the smallest void space—should be considered the best.

Shrinkage: There should be none. Measurable shrinkage after curing means that the mixture contains too much clay or too little cement. or. Both.

For other structural testing techniques, please refer to the "Building an Earth Home Manual" (mentioned in the article), or talk to your local building inspector. .. In any case, this is something you have to do sooner or later.

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