Making Adobe Bricks?

Question: What do you know about baked or fired adobe brick?

Answer: Baked or fired adobe brick is found in several parts of the world. I am only familiar with that from Northern Mexico which is imported primarily into Southern Arizona and New Mexico. It is also called "quemado" and is mentioned in the NM adobe addenda to the building code. It plinks when you strike it, it's not damaged by water but it is porous so that if it rains, soaks in, and freezes it spalls or bursts completely. Mostly it is seen as a coping on top of garden walls or sometimes on the parapet walls of homes. Often there is accelerated water erosion on the natural adobe brick course just below the quemado. That is called coving.

Lots of energy is needed to fire the bricks. The Mexican technique is to stack the adobes to be fired and then build a mortarless vault of adobe over them. A flatbed truckload of firewood is ignited at one end and a simple chimney at the other end gets the fire roaring through the adobes for perhaps three days. After cooling the adobes are shipped north. The adobes which formed the vault are then stacked to be the fired adobes in the next cycle.

An interesting observation of this process is that the outer layer of vaulted adobes never vitrify more than the inner quarter-inch if even that. It is only the interior stack that vitrifies. Nader Kahlili has a book on fired houses, but I think that the Mexican experience shows that it would be nearly impossible to do that.

Meantime, the Mexicans have to keep going farther from their villages to find sufficient firewood for the process. The hills become denuded as was the case in Rome. So most folks don't build the entire home of quemados, just the exterior walls or perhaps the above mentioned wall copings.

Add to that the fact that vitrification changes the nature of the adobe bricks ability to transmit heat. It speeds up the thermal diffusivity. That's too bad since it is the sluggishness of adobe that makes it stand out above all other masonry materials as a storage medium for heat especially in the passive solar home.

Question: My house design has a basement. Foundation, stem wall with insulation, then dig basement, use soil for the adobe bricks. Thought it might be easier to purchase bricks if price is reasonable.

Answer: Your idea of making adobes from the basement excavation is excellent. With a little asking around, you might find someone who will make adobes for $.25 to $.40. With a pile of loose dirt, all that is needed is a wheelbarrow, shovel, water, and a form to make four adobes at a time. Once people get the hang of it, two can produce about 500 adobes per day. The secret is not to mix. If the excavated soil is the right blend of clay and sand (30% / 70%) water can be poured into a small area of the pile and when it soaks in, just shovel it into the wheelbarrow. That plus the action of pouring the mud out of the barrow and into the form is all the mixing that is needed. If the soil needs sand or clay, let the excavator machine blend it dry.

Question: Where can I get a hold of a Cinva ram and for how much?

Answer: They are being built somewhere in Africa. Cost and location unknown. We have a Cinva Ram here at Northern Community College in El Rito, NM. Come and try it. It has convinced a number of people to look for a different way to make adobes. I personally think two guys with a loose pile of dirt, a wheelbarrow, a 55-gallon drum of water and a form that makes four adobes at a time can produce adobes faster than a Cinva Ram. Most Cinvas make an adobe about 8 or 10 inches long, 5 inches wide and 5 inches tall. Most codes require a wall at least 10 inches wide so it takes a lot of CR bricks to make a wall. Standard New Mexico adobes are 10x14x4.

Question: I am a 14 year old boy and I live in a rural area. I want to build a small house for "self-sustained" living. I made 16 bricks to start off with and they seem to be drying fine. However I spent forever mixing them. I am very happy to see your suggestion about "not mixing" that will save a lot of work. My main question is this: where I am we have "quack grass" all over the place and it's not perfectly level. Can I just place my form over the mowed grass and start throwing it (the adobe) in, or do I need a tarp to put it on? Thank you very much and my next web stop is the adobe message board which I started out to find!

Answer: You are off on a wonderful enterprise. I was making models of adobe homes when I was 10 and 11. Sometime around age 13 I started making full sized adobes in the back yard. My dad got mad when it killed the grass but after a while he mellowed when he realized that he did not have to mow it any longer! Most any type of construction is hard work, and adobe probably tops the list. But the harder you work at it the more it will mean to you when you are done. Making the adobes is usually the hardest part of adobe homebuilding. Try making your adobes right on top of the quack grass. The first time around the grass embedded in the bottom of the adobes might make it hard to lift the adobes or the bottom might be pulled off. Sooner or later, the grass will quit being a problem if it is one in the beginning. The tarp will make the adobe lift up for sure but they will take longer to dry. A lot of moisture in the adobes is lost downward into the ground. The wicking action of the ground is equal to the drying action of sun and wind at the top. You are invited to join our adobe discussion and support group. We are at:

Question: What are some of the potential disadvantages of using a compressed block machine to make adobes, and how would these blocks handle a warm humid summer like we have here in Wisconsin?

Answer: The blocks should do okay in your climate. Like any wall material, they need to be kept dry after manufacture, as the wall goes up, and for the life of the wall. Since the blocks are made with high compression, sometimes when they get wet, they "blossom" or expand as unresolved internal forces realign themselves. Keep them dry and you will do fine. One reason that just a slurry is used instead of thick mortar is that there would be enough moisture in regular mortar to cause blossoming due to the uptake of the moisture into the blocks. Some blocks have grooves and they go together without any mortar at all.

Something positive could also be said about CEBs like how they provide the same benefits as adobe. CEBs also allow people in wetter climates to produce blocks, and lots of them, because the blocks do not have to dry (which works well in the SW but not as well here). Like any building material, CEBs must be protected from moisture, however, they can be stabilized with Portland or lime. I have had no problem laying CEBs in mortar or a slurry. The only time I have seen the "blossoming" effect is when the blocks were drenched or submerged in water. So, when you say moisture I think it is important to be specific as to moisture as vapor (humidity) or moisture as liquid (rain, snow, broken pipe, etc.)

Question: Where do you find details about making bricks, you said 2 people with a 4 brick mold could make 500 bricks a day. Can you take the mold away as soon as the mud is put in and leveled?

Answer: You just have to fool around with the amount of water in your brick mix to get it stiff enough to stand up when the mold is pulled. And just plastic enough to work it into the mold without too much trouble. Invest an hour or two in fooling around and you will have the right blend for your soil. Also if there is too much clay, the bricks crack. You can experiment with adding sand, small gravel, and some straw to keep it from cracking.

Question: I am seeking a source in central Texas (or anywhere reasonably close) for stabilized adobes. I helped a relative build a small adobe house in Alpine, and saw his own 2000+ sq ft house near Marathon, and an adobe home is the only way for me to go. I don't think I'll ever get the combination of time, materials, and weather required to build my own blocks like my relative did, so a source is desperately wanted!

Answer (Neal): Garten Gerdes in Burnet has equipment (lay down machines et al) but has never produced commercially. The adobe he has made and used on his property is very nice and uses the "fines" from the processing of limestone for road base (also sold and used as agricultural lime). His mix (roughly 70% fines, 30% caliche and 3% AE for stabilization) is very similar to that used at the Adobe Patch in La Luz, NM back in the 70s. It makes a very nice block. The material is readily available since there are rock crushing plants all along IH35 through central Texas. If you want to do it the old fashion way, I'll help you build some forms and get a mix put together. I also know of a form system called the Mold-Master here in Austin that might be available that would be an alternative to regular ladder forms. Not necessarily better, just different. If you only need 2-3k adobes, you could probably knock it out in a summer of weekends or hire some labor to get it done faster. Having a flat space to lay the adobes out and cure them is a necessity too.