ADOBE MACHINE Q & A

Here are answers to some of the questions that arise when considering Compressed Earth Block Machines in general and ours specifically.

Q. What kind of dirt do I use?

A. Most machines will make a block of some sort and most will make a good block given the right kind of dirt. Typically the following criteria are used when choosing the right dirt:

1. Clay content - 30% is optimum. We have used dirt with as much as 70% clay and as little as 20%.

2. Water Content - 6% to 10%. Too wet and you have a soft block that has to dry before placing in a wall, too dry and the block will fall apart. The water is what causes the clay to yield making a solid strong block.

3. Sand content - the rest of the mixture can be sand with some gravel. Remember the clay mixes with the sand so larger rocks decrease the shear strength of the block while increasing the compressive strength.

4. Straw, leaves etc. - NONE. Organic material will not remain compressed and will crack the block, usually immediately.

The best material we have found is well decomposed granite near or downstream of granite formations, Granite is composed of three main minerals: Feldspars, Silica, and Hornblend. The feldspars decompose to an aluminum silicate (clay) and the silica and hornblend decompose into sand. actually the hornblend adds iron and nickel to the pot, the more hornblend the darker the soil and so on.

For a more complete essay on limestone/chalk soils see the page at Soils

To Test:

1. In a glass jar (quart or liter) fill 1/3 with dirt, fill to the top with water.  Shake, swirl until all the dirt is suspended in the water and then leave to settle for a few hours. The different soil types will be layered with the clays on top, with the ratio of clay to sand evident. if you put a little salt in the water it will cause the clays to settle faster.

2. When out in the field squeeze some freshly dug "moist" dirt in your hand.  If it remains in shape you probably have good dirt. If you can make a 3" long cigar and hold it by the end and it will not break you probably have a good block candidate.

3. In the same field, with the same dirt, add a little more moisture then try to ball some of the dirt between your thumb and fingers.  If the dirt balls then your clay is sufficient, if it crumbles the clay is too little and if it smears the clay is too much.

Some clays don't yield as well as others so part of the clay acts like sand so press some blocks and experiment. If the block cracks (lots of little cracks) and there are no organics then the clay content is too high. This doesn't necessarily mean the blocks are no good it just means the clay is a little high. The plain truth is that you can make very good blocks that are ugly and very pretty blocks that are no good, the key is the clay. If the block falls apart and the moisture content is adequate then the clay content is too low. You can have too much clay but you can't live with too little (unless you add portland).

Clays add one thing that most other minerals do not and that is plasticity to the soil, if you are rolling the soil in your hand and it will stretch to a pencil shape you have sufficient clay to make a block and if that little pinner shows a sandy grainyness then you will probably have enough sand in the mix. If the soil is high in clay and a little damp the addition of crushed stone (with an even mix of coarse sand up to 3/8 gravel) of about 10% will make the difference.

Q. Don't the blocks disintegrate when they get wet?

A. Yes they do unless you add something that will make them waterproof, or you can keep them dry under a roof line. Here is what I do: When  am building a home i will mix 6% portland cement with the soil that will become the first 2 courses of the walls from there up i use soil alone unless i am in a very rainy area where i will add about 3% cement to the soil.

      The only way to know if the block is truly waterproof (stabilized) is to soak it in a bucket of water for 24 hrs if it disintegrates then add some more cement if not then you know you have a good block.

Q. Do I need to add cement to make them strong enough?

A. If you can drop a block from waist high and it doesn't break it will be plenty strong. I usually wait 3 or 4 days to perform this test since fresh blocks are a little tender. Cement or lime will certainly make then stronger and for floors and pavers we commonly use a mix of the 2, but remember this, Cement adds embodied energy and cost! So use what you need for what you are doing. As John McEvoys Grandma used to tell him:"enough's as good as a feast"

Q. How long will the machine last?

A. This is directly dependent on your maintenance schedule.  How careful can you be when adding oil to the system, hydraulic or engine, to clean all the dirt from the reservoir cap BEFORE you open it?

We have machines that are still working after fifteen years. Yes the molds do wear out and the lifespan of the mold is directly proportionate to the abrasiveness of the dirt. you can count on 50,000 block and could exceed 500,000 again depending on the dirt. We are continually working to improve the lifespan of our molds but do offer replacement mold assemblies for a nominal charge.

Q. How much pressure do you use to make a block?

A. This answer is dependent upon your moisture content and dirt quality. With optimum dirt you would require about 1700 PSI to make a quality block this is based on the formula: system pressure * cylinder area / area of press foot. A dryer mix would require more pressure and a wetter mix less. Our machines are set to press at 2800 PSI (system pressure). This is adjustable down to 0 and up to 2700.  3000 PSI is the maximum pressure.

Q. Will you teach me how to operate this machine?

A. We would be happy to spend a couple of days with you at our facility in San Ysidro N.M. USA and instruct you on the operation of your new pressed earth block machine. We are also available by contract for consultation, training and project management.

Q. What if the machine quits working or doesn't work right?

A. We can be reached by telephone, fax, or email any time any day, All machines have a one year warranty for workmanship at our facilities in San Ysidro, NM. 

Q. What are the applicable codes?

A. There are few specific codes for pressed earth block but the codes for "adobe" mudbrick are substituted and are usually adequate although overkill in some areas. The only states we know of that actually have any "adobe" codes are California, Arizona, New Mexico, Texas and Colorado. New Mexico now has a pressed earth block code that is available at this link and from the state construction industries division. If you know of others please let me know the state and the codes if possible.  You can email me at: dan@adobemachine.com

Q. What about earthquakes?

A. Here is a web document that well defines the problems as well as the remedies for earthquake related earth construction. The one thing that is most apparent is THICKER IS BETTER! Some Thoughts On Adobe Codes

Q. How do I build an adobe house?

A. We have a library of information as well as 30 years of accumulated knowledge of CEB construction and production techniques which we will be happy to share with our clients. 

There are many sources on the Web as well as books and periodicals available for your information.  Here are a few:

www.greenbuilder.com

Pressed Earth Block Vol 2 Design and Construction click on EARTH on the Left side of the screen then scroll down to the file # D.10

Links will be added as I find people who are actually in the business and have a web site. These sites are loaded with information that was learned the hard way.  

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