Ways to Make Adobe Bricks

Quentin Wilson and Associates, specializes in solar adobe design and construction. He grew up in the South Valley of Albuquerque, New Mexico where he watched adobe bricks being made. In the fifth grade, he made miniature adobes on cookie sheets in his mother’s oven in order to construct house models for a class assignment. By age thirteen he made full-sized adobes in the back yard and ruined the grass. Later, he traveled a bit, went through the Army, and graduated eventually from the University of New Mexico with a major in physics, minors in math, chemistry, and education in 1970. After teaching high school two years and community college math for three more, Quentin moved into professional solar adobe construction in 1976 as the Project Manager and Instructor for the Sundwellings Demonstration Project at Ghost Ranch, Abiquiu, NM. He became a licensed general contractor in the State of New Mexico in 1982. He has been building homes and teaching seminars and workshops ever since. In the fall of 1995 he established and taught the full-time Adobe Construction Program at Northern New Mexico Community College. His website, quentinwilson.com, lists the course schedule and many other resources related to working with adobe.

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

A: 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.

Q: Is there any special treatment or chemical to be used in making adobe? (or just sand and clay and then fired?)

A: Sand and clay. Not fired. Just baked in the sun. The largest energy input is solar followed by human metabolic energy. How green can you get? Just a shovel and wheelbarrow, a bucket of water and a simple wooden form. With no wood you can form adobe by hand as in Mali. With no wheelbarrow you can move earth in baskets as did the Anasazi of the Southwest United States, with no shovel you can use a pointed stick as many cultures do worldwide. With no bucket or no water one just waits for it to rain and then makes the mud.

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

A: 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.

Q: Where can I get ahold of a Cinva ram and for how much?

A: 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.

Q: 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!

A: 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 imbedded 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.
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Q: 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?

A: 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.

C: 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.)

Q: 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?

A: 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.

Q: 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!

A: (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.

Q: Looking for a new or used Lever-action block press for making soil cement blocks. No luck as of yet, any advice is appreciated.

A: We have a very old CinvaRam here on the El Rito Campus of Northern New Mexico College in case you want to experiment with one before you buy. A number of us are not convinced that the press speeds things up especially if the soil has to be blended to work.

Here is a source for CINVA Ram Plans in Thailand

Q: I wonder if you can advise me regarding some trouble I'm having with my experimental adobes sticking to the molds when I try to pull them. Can I use any oil? I brushed the molds with used cooking oil but they still stuck
after only 20 minutes in the molds. Maybe they need thoroughly soaking in the oil? Does using cement mean that they swell and stick even more? If, when working on site, would it work if I dipped the molds in a drum of oil thereby thoroughly soaking the molds, or would so much oil affect the adobes in any way?

A: My best guess is that the adobes have a high clay content. 30% clay and 70% sand gives the strongest bricks but higher clay content gives more water resistance in a wall that is not protected from rain or other moisture sources. At those higher clay levels the adobe bricks will usually crack unless they have straw added to control it.

I did not fool with oil as it was one more thing to have on the work site. My technique was to thoroughly soak the wooden form in water before the first bricks. The mud needs to be stiff enough to be able to lift off the form right away. With a 55-gallon drum handy or a bucket and rag it can be quickly cleaned or wet. Once my system was going and there was a low enough clay content so that the bricks did not stick, the form seemed to stay wet enough as it took up moisture from each brick. Then I would only clean it off if a bunch of mud stuck in a corner.

The addition of cement will not make the bricks swell as far as I know. However, it might make the bricks a bit more sticky. Later, when I had enough forms to make 90 adobes per evening, I made a much slurpier mix and let the adobe sit overnight before pulling the forms. The forms nearly always came clean enough so that I did not have to clean them. Just keep fooling around as each soil and mix has its own personality. Sooner or later you will find the combination that works on your soil.

Q: Are there any resources for brick or adobe making molds. We currently want to manufacture about 5,000 Sf of bricks for our landscape area. Had read in Mother Earth News about a brick making machine made in Austin, Texas in the late 70's called the Mold-Master manufactured by Methods Manufacturing which was a 3 wheeled mold machine. Could make 300-500 bricks per hour! Anything available similar to that?

A: The Mold-Master was the brainchild of Howard Scoggins. It was great but really needed a couple of gorillas to make it work. Now there are a lot of machines on the market with engines and hydraulics to make compressed earth blocks. I favor the suncured made on the ground bricks. There is nothing on the market right now like the Mold-Master that I know of. Two people with a loose pile of earth, a wheelbarrow, a source of water and a wood mold that makes four bricks at a time, can make about 500 bricks per day. It's hard work, but it can be done. Or at two hours a day, two people can turn out about 100 bricks once they get the hang of it and the rhythm.

Q : We are trying to secure funding to get a CEB machine to Canada. We need to know if the CEB will withstand a Canadian climate (western Canada at this point) and what mixture is in the block is the main question we are being asked.

A: The real question is can anything, including humans, withstand a Western Canadian climate. We are down here in sunny New Mexico where it was a balmy negative 12 Celsius at dawn this morning. Human powered CEB machines are priced around $90US in parts of Africa. Engine powered hydraulic units made in the USA are a bit more pricey. Best blocks will be around 30% clay and 70% sand. There are many variations including silt and a bit of organic matter that can be tolerated in a CEB. It is just a matter of fooling around with perhaps some lab work included to determine the best ratios. If you can get a block out of your soil without having to modify it, then even if it does not give the highest lab test ratings for compressibility or modulus or rupture then it is the best block. Any sort of wall material in Canada needs to be protected from moisture moving up from the ground, moisture penetrating through the exterior wall covering and moisture coming down from the roof system. I am confident that the Canadians have worked out these systems very well. Otherwise their wood houses would mildew and rot, steel houses would rust and fired brick houses would spall apart.

Q: Firstly, my plan is to build a small (10' diameter dome) using earth, with an earthbag stemwall filled with pumice(on site). The bricks are cast in a large form and then cut in trapezoids, with bricks getting smaller as I go higher.

A: I think your idea of cutting the trapezoidal bricks is great. We tried to make them in trapezoidal forms and each form locks a person into a narrow range of dome diameter. Cutting them makes more sense and saves building multiple forms. Eventually we settled on rectangular bricks, 7x10x4, and put them together with trapezoidal mud mortar.

Q: My Jr. High grandson chose to make a pyramid out of adobe for a school project. Where can we purchase clay to make adobe bricks. We live in KY and have lots of rocks but little if any clay.

A: I am assuming that this is a model pyramid. Most craft stores that cater to ceramics hobbyists have clay. There must also be several clay suppliers that sell clay to professional potters in Kentucky especially the closer you get to Berea. Some suppliers will roll it out into a 1/4 or 3/8 sheet. This is perfect to cut into rectangles 1/2 by one-inch or 3/4 by 1-1/2 inch. These make perfect miniature adobes. They do not have to be kiln fired. They will be strong enough air dried just as most pottery is before it is fired.

We are delighted to have heard that an adobe house was discovered in Greensburg, KY this summer. It is on the property of a Presbyterian church there and hopefully has been saved. It was being torn down until the adobe discovery was made. Just think, Kentucky has an adobe heritage!

Q I heard of a building method, but am not sure how much of it has been done. I was told its an old Spanish method. Anyway, I was told the walls were built and then wood stacked against them ..length wise...then lit and they would burn slowly for at least 3 days or more...the mason would watch the fire ...making sure it burned slowly...then when it was done it was like fired pottery...cerami ...all the walls would be like ceramic pottery. Have you heard of this method and can you give me any more information about it?

A: This is a new one for me. There is a slim chance that the firing would vitrify the exterior 1/4-inch of the wall but almost certainly no more than that. Nadir Kahlili made himself famous for his system of firing an adobe structure using a special kerosene nozzle to create a lot of heat for a long time on the interior of the structure. I don't think any of the firings vitrified more than a 1/4-inch. Some bright Californians did wrap a structure with the insulation used for a ceramic kiln and they achieved more vitrification but I don't have any details at hand. The cost of kiln insulation is substantial and would be prohibitive for a single structure. There might be a grand opportunity for an itinerant insulationist who could travel the country thermally wrapping structures to be fired.

The system you describe at least deals with the exterior of a structure which is where the rain hits is so it would be a better approach than Kahlili's in my opinion. It would really be nice if you would give it a try and report back on the results. Certainly no one in this country has done it or I would have sensed the vibrations from the effort. I would caution against having any wood or concrete in the structure. Wood burns; concrete returns to powder. I would love to make contact with your informant to get further information.

Q: I am planning to start building with adobe in my country, Panama. A friend of mine and I are thinking about opening a small business. However, we are looking for an adobe brick making machine. Is there any one in particular you can recommend to us.

A: The most famous of the adobe making machines is the human-powered CinvaRam developed in Colombia, I think by an Engineer named Ramirez for the CINVA non-governmental agency. I think CINVA is still in existence. There was the United Nations Handbook of Soil Cement Construction that helped USA Peace Corps volunteers use the machine. There are lots of diesel powered Compressed Earth Block machines now being manufactured in various parts of the world, especially in the USA. Perhaps the best is at www.aectceb.com . The owner of the company, Lawrence Jetter is very helpful with information and has developed a nice handbook.

Meantime, just get a pile of loose dirt, an old oil drum with water and a 20-liter bucket, a wheelbarrow, a shovel and a wood form that makes four adobes at a time. Try adobes that are 20cm by 40cm by 8 or 10cm. The best soil will have around 30% clay and 70%sand but there is usually some silt and organic material in most soils and the mix does not have to be exact. Too little clay makes bricks more susceptible to rain damage and too much clay makes them crack as they dry out so that they are not useable. Some CEB manufacturers will tell you that their machines can make good bricks with a wider range of soils than sun cured bricks. In most cases that is not true and press machines need a more accurate soil blend. Making adobe bricks and building adobe homes is labor intensive. That is good. It provides more jobs. Brickmaking is career of modest stature in villages worldwide, or at least it used to be. I declare that the world is now entering an era of machinery saving devices: namely humans. Most of the world needs more labor/jobs. A large adobe production machine can put four to ten people out of work.

Q: I am a 10th grader and want to do a science experiment on the strength of adobe bricks with various materials added to the mud mix. However, it is the middle of winter here in VA, and sun drying the brick doesn't seem possible. As an alternative, I thought I could make a 4'x8' box of plywood and place either an encased plug in oil or a plug in register type heater to dry out the adobe in my unfinished basement. The bricks won't be full size, but scaled down some. What is your opinion or suggestions?

A: It is encouraging to hear of your interest in adobe bricks. Adobe brick homes were built in your area but not great in number. A doctor with the Department of Agriculture built an adobe home in Washington, DC in the 1930's. Hill Top house at 1300 Rhode Island Avenue NE was built of rammed earth before 1780 and would have been the oldest house in the DC area had it not been torn down in 1953. It is thought to have served as Monroe's temporary White House in 1812 and as an embassy in the early 1900's.

Your idea to build a plywood box should work fine. I would suggest the plug-in oil type of heater since it does not get hot enough to be a fire hazard.

You might be able to proceed without having to build the box. It is possible that bricks will dry out in the heated rooms upstairs. Standard bricks in New Mexico are 14" x 10" x 4". They take about a week to dry in the New Mexico summer sun. If you made bricks that were 7" x 5" x 2" they should dry out enough in a heated room so that in a few days they would be strong enough to carefully turn up on edge. Then they will continue to dry with warm air all around them so that they should be hard in about a week's total time. If not, through careful negotiations with your mother/father, they could be finished up with about 30 minutes baking in an oven at around 250 degrees Fahrenheit. You might choose to make the bricks even smaller.

Bricks are considered to be sufficiently dry at 4% moisture content. If you take one brick from a batch and weigh it, then put it in the oven for half an hour at 250 degrees and weigh it again, then back to oven for 30 minutes at 300 degrees and weigh it a third time. If there is little change from the second to the third weight then you know that you
are near zero moisture content and then the loss in weight from the first weighing to the third divided by the weight of the third weighing will give you the percentage of initial moisture content. In your climate with its higher ambient humidity, adobe bricks will equilibrate somewhat higher than 4% moisture content. I don't have enough experience to know but if you determine that, it will be a contribution to the science of adobe bricks above and beyond what you discover about how additives modify strength.

Reply: Thank you very much for your informaiton on adobe bricks as it was very useful. I used your information on my science project, and I got second place at the Piedmont Regional Science Fair!

Q: I am in the 11th Grade and currently enrolled in a class called AP CAPSTONE, where each
student has the opportunity to research a topic of their choice. My study encompasses the efficacy of how Banana Compressed Earth blocks could potentially rebuild slum villages in the Philippines.

A: I am a strong proponent of the use of adobe bricks which are sun-cured on the ground but I have some interest and experience with Compressed Earth Blocks. Adding banana fibers probably will not hurt CEB's but it will entail an additional step: thorough mixing or blending of the fibers into the earth to be compressed. Brazilians have tried shredded plastic shopping bags and there is a movement in the United States right now to use hemp fibers. Machines exist that are mounted on trailers and with their powerful diesel engines they can produce 5000 blocks per day - enough to build a modest home. So, CEB's are here and I might as well get used to them. Let's see what bananas can do.

I assume that you live in the Philippines. CEB's require clay to stick together as a block. Some producers of CEB's add cement to the mix and follow formulas in the United Nations Book: "Soil Cement, It's Use in Building." Many islands in the Philippines have abundant clay that will be perfect for CEB's Other islands, perhaps such as Palawan might be dominantly sandy. I hate to see the use of cement unless it is absolutely necessary. In the interest of reducing the impact of construction materials on the planet, cement is one of the products we would most like to reduce.

Q: I would like to start experimenting with my own bricks, but I'm having a hard time sourcing them. Do you have any suggestions for where to buy raw mud earth to mix for my own bricks?

A: Most likely you can look in any direction and find what you need: 30% clay and 70% coarse sand make the best adobe bricks, mortar, plaster and floors. Silt and organic materials can be tolerated but are not desirable. Other proportions will work but might require modification. If clay and sand are not readily available at your feet, you can usually find what you need by digging down.

If there is a sand and gravel company operating near you, you can ask them for crusher fines or the old formulation of base course which includes clay. They will let you pick up some yourself and when you go into production they will send you a dump truck full. In some locations there will be an old adobe building crumbling away. Bricks can be salvaged and reused and the piles of dirt around the building can be mixed with water and recast as bricks or used for mortar. The proportions of clay and sand can be expected to be perfect since it worked to make a building in the first place.

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