Mixes for Adobe?

Question: I want to make miniature adobe houses for my son's Santa Fe train city. I cannot seem to find any specific directions. I noticed that your article on this site said you had made them before. Can you help me with instructions?

Answer: Little adobes can be made many ways. The simplest might be to fill a cookie sheet with mud. It is easiest if the cookie sheet has low sides around it, about a half inch. Then the mud can easily be scraped off level with a knife, trowel or short board. Little adobes of most any size can then be cut with a pizza rolling knife. An inch wide by an inch and a half long is a good size. Then put the mud in the oven at about 225 degrees for 10 to 20 minutes. The bricks may have stuck together a bit but they will break apart easily enough. The mud mixture should be mostly sand - about 70% and the rest clay. Many soils out your back door will work but sometimes a little sand can be added if the soil has too much clay. It is clay that causes bricks to crack. Just fool around a bit until an appropriate blend is discovered.

Question: I am a thesis student of Architecture at Auburn University. I am pursuing my thesis in the Rural Studio, which focuses on Green buildings and housing the unfortunate poor of Hale County. Our project is in Lee County, AL, and consists of transitional housing for persons with disabilities. Me and my team are interested in the construction methods of adobe bricks and cast earth. The soils around locally are high in clay content. I was wondering what construction methods would work best in Alabama. As well as would these be viable methods. Any information that you could provide would be greatly appreciated.

Answer (Kelly): I have been aware of and impressed with the work of the Rural Studio and Sambo. I am very sorry to see that he died, but glad that his work will continue. I have much respect for what you are doing. I would say that adobe in particular would be an appropriate material for you to work with. The caste earth really requires the use of heavy equipment and an experienced crew. A few people can make adobe bricks and lay them very inexpensively and create substantial and comfortable housing. I suggest that you see if you can locate a cinva ram press to make the adobe blocks, since it is fast and makes very solid blocks without a lot of drying time and no need for forms. The clay content of the soil needs to be around 20% to 30%, so you might do a little test with some of the soil in a jar of water, shake it and let it all settle for a few hours to see exactly how much clay there is in the soil (the clay will form a layer on top, over the heavier soil particles). You may have to add some sand to the mix. Good luck with your project.

Question: I have spent some time researching earthship homes and was seriously considering that but the research I've done today has me considering adobe. As they seem to be a bit easier perhaps, in construction. Tire pounding would probably be good exercise but I don't know if I'm up to it. Ha! I have 10 acres in the country and plenty of dirt but not sure if it's "the right dirt" or does it matter? Probably just mix with straw? I am curious.

Answer: 30% clay, 70% sand, gravel, decomposed granite makes the perfect brick. As little as 10%clay will also work. Some silt can be tolerated in the mix. Straw is only needed to keep the bricks from cracking if there is more than 30% clay. Too bad Moses didn't know that. Maybe its better. History would have been different.

Question: Aloha. Currently residing in up country Hawaii. Have experience in rammed earth from a former life in Tucson, but am curious about "field" tests for compaction of native soils. There are 5 different bioregions on the island of Maui alone and I am only hand tamping the forms so far. So basically I want to hand tamp local stabilized soils for the purposes of sculpture, not structure. Any thoughts on how to check my available soils before I hand ram something that lacks the desired integrity?

Answer: Small samples. Squash em, kick em, leave em in the rain.

Question: I am busy preparing a business plan to build low cost toilets using earth blocks compressed with 7% cement, do you think I can use those type of blocks to reinforce the pit which will be 2m, do you think the small toilet can collapse after 2 or 3 years because of the daily wet environment, I did not find any information on the internet concerning compressed blocks under wet environment.

Answer: These blocks might work. I am very happy to hear that you would be using them to build the toilets. However, it is known that CEB's sometimes "blossom," another word for expanding, when they get wet. This is because there are a lot of unresolved interior stresses due to the normally ferocious pressure with which the blocks are made. A block that is subject to moisture might be better made with a higher cement content and made with the compression force lowered.

Each and every soil reacts differently to the introduction of cement which is basically not compatible with the clay content. For this reason the book, Soil-Cement, It's Use in Building was developed by the United Nations in 1964 and was used as a handbook for Peace Corps volunteers making bricks around the world. It was prepared and first issued in Spanish by the Inter-American Housing and Planning Center, Pan-American Union, Department of Social Affairs. Later versions in French and English were prepared by the United Nations. In English it is United Natinls Publication Sales Number 64.IV.6. ($1.50). It spends considerable time on figuring cement/soil ratios appropriate to different soils.

Question: I am making stabilized adobe (adding asphalt emulsion) in Todos Santos, B.C.S. Mexico. I want to leave the adobe exposed on the outside and have flat roofs. Will the stabilized adobe hold rain? Do I need to add some sort of water sealant?

Answer: Adobe with about 4% asphalt is quite waterproof. In the USA the asphalt is quite emulsified through chemical magic and mixes easily with water. The asphalt I have seen in Mexico is not as thoroughly emulsified and has a bit of a kerosene smell even after the adobes have cured. It is sometimes referred to as cut asphalt instead of emulsified asphalt. The walls will work well in areas that have rainfall under 50cm annually if you use asphalt in the mortar at the same rate as the adobes. Do not put on an exterior sealant. Many types of sealants have been tried and if they do not breathe, any moisture that gets into the adobe cannot get out and breaks the bond of the sealant at the surface of the adobe. Asphalt will do the job. With your project, you might wish to join our adobe discussion group at: https://groups.yahoo.com/neo/groups/adobe/info

Question: I was wondering how much asphalt emulsion is needed as a ratio to make mud cement and how much does a 50 gallon can of asphalt emulsion cost.

Answer: Each soil will react differently to asphalt emulsion so in New Mexico the definition of a stabilized adobe is a functional definition. That is, an adobe placed on a porous, water saturated surface for seven days may absorb no mare than four percent moisture by weight. Adobe producers will tell people that they use 2 to 10 percent asphalt emulsion but do not mention if that is measured by volume or weight. I find that 8 to 16 liquid ounces is about right to stabilize a cubic foot of my soil's adobe mud. That is about 1/2 to 1% by weight. It is not fully stabilized but will give enough protection to preserve the adobe for my lifetime. Another way to add is to put 5 gallons of emulsion into a 55-gallon drum and fill it the rest of the way with water. That way the water has 10% asphalt. It is a little nicer to work with than full strength emulsion.

The cost of 55 gallons of asphalt had been about $75 until the prices of oil products began to go up the last couple of months. My guess is that it is well over $100 by now. A source of emulsified asphalt in New Mexico is Elf Asphalt on North Edith Street in Albuquerque. Their minimum sale is by the 55 gallon container. You have to have your own barrel hopefully one with a removable top. Plan on splashing some asphalt on the cab of your pickup truck as a badge of honor.

Question: I live in the Pasadena area of southern California and am interested in working with stabilized adobe first in a low retaining wall and perhaps more ambitious projects later. Where can I buy the emulsified asphalt in relatively small quantities (1 gal - 5 gal) locally? Thanks in advance for the help.

Answer: If there is an Elf Asphalt plant anywhere in your area, they may sell you five gallons of emulsified asphalt. There might be some other bulk asphalt plant that supplies road or driveway repair contractors. If not, some formulations of roof asphalt - sometimes called cold process - are emulsified. One just has to read the can to see if it can be thinned with water. A lot of the original work with adding emulsified asphalt to adobes was done in Southern California. Largely a group of retired chemists from Chevron.

Question: I live in Northern California and want to build an outdoor adobe oven. The soil here is fairly organic with lowish clay and sand content. Local construction supply stores give me a blank stare when I ask about availability of adobe type soils.

Answer: Sand and gravel producers usually have something that will work. They might call it crusher fines or crusher trash. Old fashioned base course worked great but at least in New Mexico base course now has less clay and will not clump together. You are looking for a soil that has 30% clay and 70% sand. Gravel particles can be tolerated up to 1- or 1-1/4 inch diameter in adobe bricks. You can use far less clay if you are going to stucco over the horno for weather protection. You can't use much more clay without experiencing cracking. 30/70 also makes a good mortar to stick it the adobes together. For mortar you might find it useful to screen the material through a 3/8- or 1/2-inch screen.

If a sand and gravel producer can't help you, the material is on your property. You just have to dig below that pesky top soil down to sand and clay and gravel strata below. Or find a riverbed or wash nearby. Or make friends with a gravedigger. The Spanish who put the California in California could make adobe bricks most any where in the state.

Question: I am interested in building an adobe exterior wood fired oven for outdoor use in the Boston, Massachusetts area. I cannot find any one who has any knowledge of adobe availability out here and wanted to know what other materials may be suitable to create the shell of the oven specifically the clay component of the mixture, is pottery type clay appropriate or something else that is available in larger size formats?

Answer: A mixture of 30% clay and 70% sand/gravel will work. Sometimes that is called base course at a gravel pit. Pit run or crusher trash will usually also work. We are discussing hornos (adobe ovens) at the moment at http://groups.yahoo.com/group/adobe/. An English style oven was built in MA or ME and was featured on the PBS program the 3000-Mile Garden a few years back.

Question: Are you familiar with liquid glass added to adobe as a stabilizer? If so, where can I get some? I'm building in Terlingua Texas, which is a desert.

Answer: I thought that I had heard everything but this one is new to me. You are near Simone Swan and her adobe dome and vault projects at Presidio. Not to mention Pat with her adobe at the end of Twisted Road at one of the villages between Ter and Pre. I will ask my friends about liquid glass which reminds me that we learned in Science Class that glass was a liquid.

Question: Water glass is probably what she was describing. Sodium silicate?

Answer: My guess is that waterglass without modification will not do the trick. Still no one with actual experience with the material with respect to adobe.

Question: Can Compressed Earth Blocks (CEB) be stabilized in such a way that they can be directly exposed to the weather for use in home-building, retaining walls, driveways, etc.? If so, what is the stabilizer to use, and if not what is the best stabilizer for moisture protection and what other steps must you take to protect the walls?

Answer: Most CEB's are stabilized with cement. There have been problems with exposed walls even with cement. If the walls get wet, some of the pressure of unrelieved stresses at the particle level in the CEB's is released and the bricks "blossom." That's another word for expanding and flaking apart. My own solution would be to stucco exterior wall surfaces of CEB's. CEB practitioners might have more ideas.

Question: I intend to stabilize the adobe with pozzuolana ash like Rice Husk Ash or Silicafume. Do you have any experience on this problem? Please give me some advice! Will I succeed?

Answer: I have never tried this so am unable to predict the outcome. I have always been happy with unstabilized adobes. Just back from Cappadocia in Anatolia where there are 3- to 4-thousand year old adobes without stabilization. They have had constant maintenance even in that low rain climate. However, nearly everything works with adobe so with a little experimenting with ratios, you should get a workable brick.

Question: I live in Barbados where coral dust is available. I am wondering if this can somehow be used in the construction of adobe brick?

Answer: Adobe needs aggregate such as sand, gravel, or stone as the component that gives strength. It also needs something to provide cohesion, namely clay. The coral dust might provide the aggregate part or perhaps it has stickiness and can act as the clay component. I have no experience with coral other than to observe it in some Navajo jewelry along with turquoise. If the coral has no stickiness, then it should act well as an aggregate. You would then need to find a clay source and there should be some in the Barbados. You would only need about 9% of the total weight of the brick. It would not be very waterproof. 30% would be better. I do know that there is some adobe construction in the SE part of Jamaica. If the coral provides the stickiness, then you only have to find lots of sand to add to it to get a great brick. Just try fooling around with the coral dust to see what happens.