Miscellaneous Questions about Rammed Earth

Clifton Schooley is a green building professional specializing in insulated rammed earth construction and architectural design in Canada and worldwide. His vision is to create environments that are beautiful, artistic, sustainable and have a positive social impact. Clifton believes that both design and construction of a building must be intimately connected to bring maximum benefit to both people and the environment. Beyond rammed earth his ambition is to become an eco-developer and influence society on a larger scale. For more information, visit:  www.rammedearth.info

Questions and Answers

Q: I have decided to build with non load bearing strawbale infill walls around a two story steel frame with the roof on. I would like your advice on the marriage of strawbale with rammed earth construction techniques. I am proposing the use of 550 mm wide slip forms with a strawbale course placed centrally, the 50 gap either side would be rammed with stabilized earth instead of rendering later with 3 coats. Do you think this would be a workable system? If so, what would you suggest as a possible formwork system and what would be the best way to ram the earth. I can see one of the difficulties would be ramming the earth at the top of the wall under the roof, but this could be rendered afterwards.

A: In my opinion, this won’t work very well. It will be near impossible to ram 50 mm of earth next to a strawbale without displacing the strawbales in some way. You would be going to a lot of trouble with forms, ramming, etc. trying to do the rendering - something that is really quite simple. If you want to consider faster methods of rendering, I would suggest using gunite or similar process, where the rendering material is blown onto the strawbale wall with compressed air. “Gunite” is a term used here in the US. Other terminology may be in use in other locales.

Q: I am trying to start up a straw bale home building business, trying to bring "green" construction to the prairies, here in Manitoba. A British publication explained the use of car tires as an alternate foundation type for straw bale homes. However, they don't have to worry about ground heaving during winter freeze and thaw, in Canada, we do. Some of the descriptions of the Earthships sound a lot like walk in basements. And I was wondering if, due to the lightweight nature of the material I wish to build the house shell out of. Can rammed earth car tires be used for a basement foundation??? And would you know where I could get the engineering info on the rammed earth car tire wall? (Like compressive strength, maximum load bearing capacity...)

A: Congratulations on your decision to use sustainable methods in your new construction business!! Especially in your area, which is a well-known source of grain production with straw as a by-product. I can see no reason why a rammed earth tire foundation could not be used for a strawbale building. There are two methods I would suggest:
1) Excavate a trench to below the local frost line; then construct a rammed earth tire wall up to the desired grade. You would have to use non-frost-susceptible fill for the rammed earth tires, and the foundation would have to extend far enough above grade to ensure that the bottom layer of strawbales stays dry.
2) If you are concerned about the depth of excavation, you could adapt a form of the "Shallow Frost-Protected Foundation." This design concept was developed in Scandinavia to reduce the depth of foundations in those cold, far-northern climates. It uses vertical and horizontal insulation to direct the flow of heat from inside the building in a manner that prevents the soil under the shallow foundation from freezing. For rammed earth tire wall engineering information, contact biotectureATearthship.org

Q: I'm interested in learning more about soil cement. I've found a couple of short blurbs about what it is and how to make it, but I have some additional questions: How long might a soil cement patio hold up in a place like Maryland that has a lot of rain/snow, and plenty of freeze/thaw cycles?

A: (Bruce McHenry)
Here is a bit about the formula:
Make it by mixing earth with Portland cement to the desired depth, add water and mix again. Tamp, and cover with plastic to let it cure properly. Use 6 to 16 percent cement by volume according to the density of the soil. The denser the soil (clay, for instance), the higher percentage of cement to use. Six percent translates to 1 part cement to 15 parts soil; 16 percent translates to 1 part cement to 6 parts soil.

Q: I want to let you know that there is a environmentally safe soil stabilizer on the market named Earthbind 100 that may be a good alternative to asphalt emulsions used to stabilize material used for rammed earth. As you know, asphalt contains many of the carcinogenic polyaromatic hydrocarbons. Earthbind does not. It is a mixture of paraffin resins and tree lignin. Earthbind has been thoroughly tested and does not contain any organic compounds that are considered toxic. In addition, Earthbind was been extensively tested regarding the toxicity on fish, mammals, and plants and it considered very non-toxic. I believe that it will stabilize soils better than an asphalt can because of the resins. I can send you a free sample if you would like to test.

A: I do not use or recommend the use of asphaltic mixtures for stabilization of rammed earth. My preference, where necessary and appropriate, is to use Portland Cement (PC). Although there are certainly some environmental concerns (embedded energy) with PC as well as some safety concerns with its caustic nature when it is being handled, it is not toxic once it is in place. And... there are no issues with smell or outgassing. Moreover, I believe that PC adds more to the ultimate cured strength of the rammed earth, and it is easier to mix with earth than asphalt emulsion.

I would be very interested in taking a look at Earthbind 100, and I would like to receive a sample. I have previously used lignin compounds for dust palliative work, where they were quite effective. I imagine that they might be equally effective for stabilizing rammed earth. Before I could recommend this product, however, I would have to receive a Material Safety Data Sheet (MSDS) and I would have to know what's in it. I would also like to see application rates and instructions as well as a price list. After I receive the sample, I'll give it a try and let you know what I think.

Q: I am a student in Napier University, Edinburgh, Scotland. I am studying Architectural Technology and as part of my final year course work I must do a Dissertation. My chosen topic is Rammed earth structures and their Ecological Footprint, my aim is to show that rammed earth homes are significantly more sustainable that that of masonry construction through doing an ecological footprint of both. I would greatly appreciate any information you have on ecological footprint possible to help me in my research, in particular the main data I need is the ecological footprint of earth as a material, I have contacted numerous places but none have been able to give me the data I am looking for. If I could get this information it would improve my dissertation to a great extent.

A: I'm glad to hear of your interest in Rammed Earth and its ecological impacts. In my own opinion, the "footprint" for earth as a construction material could vary widely... Let me set up a couple of different scenarios for you to think about...

Let the first case be the "Third World Rammed Earth Case." In this situation, on-site soil (ideally a sandy material with some clay content) would be used, probably without amendment. A relatively large number of indigenous workers would use hand tools to excavate soil for the project, move the soil about on site, place it in the forms, and compact it into a wall. The rammed earth forms would probably be made from locally obtained lumber, or perhaps scrap plywood or lumber "acquired" from more sophisticated projects that are going on somewhere not too distant. In this case, the ecological "footprint" would be quite small as long as the work crew took care not to mess up the drainage, cause a lot of erosion, etc.

Now let's go in the other direction and look at the "First World Rammed Earth Case." In this situation, on-site soil would be used if it was available and suitable. Otherwise suitable soil would be trucked in from an off-site location some distance away. Some sort of soil "stabilizer" would almost certainly be used. This would probably be Portland Cement or an asphaltic emulsion, typically about 3% by weight. A relatively small crew of hired construction workers would mix the soil with the stabilizing agent and move it into the forms using a skid-steer or other front-end loader. Once in the forms, the soil would typically be compacted with pneumatic rammers powered by diesel engine air compressors. A variety of other mechanical equipment might also be used, including a pug mill for soil mixing and forklifts to move and erect forming equipment. Finally, the forming materials would probably be more sophisticated plywood/lumber forms made from new stock or rental forms as typically used for constructing concrete walls. In this case, the ecological "footprint" might be much larger than the "Third World Case." A lot of fuel and equipment time would be required as well as significant amounts of Portland Cement or asphalt emulsion.

Please bear in mind that these are relatively extreme cases and that the actual methods used to construct Rammed Earth walls - and the "ecological footprint" could vary between the two extremes. In one case, hand tools and local materials are used by low-paid local workers. In the other case mechanized equipment and materials from remote areas are used by high paid construction workers who may come from afar. Just about anything in-between is possible. It just depends on the local circumstances.

Q: In my case I would be using rammed earth that is not stabilized although there is the use of mechanical equipment and travel costs. What information would I need if I were to try give a footprint to rammed earth built in the 'First World'? I need to get this ballpark figure for rammed earth and then work from there as I am comparing it to a building made out of concrete block.

A: Before I can do much more to help you, I'm going to need a more precise definition of what you mean by "ecological footprint." What units of measurement is it defined in, what conversion factors are used to change other measurements to it, etc. I think I know what it means... but it may mean one thing to me here in the US and quite another to you in a different place.

As far as research methodology is concerned... I'm not sure I wouldn't be doing you a disservice by providing some numbers to you that come from a relatively small number of projects that I'm familiar with. So, I'd strongly suggest that you seek out projects that will provide data for your dissertation. Interview workers and their foremen, interview the project architects and engineers, and do enough observations of work in the field so that you feel comfortable with your results.

You need to start by setting up and documenting two hypothetical projects that will result in similar buildings, one from rammed earth, one from concrete block. Just to keep things simple, I'd start with a hypothetical simple single story rectangular building design with a truss or shed roof. Make the interior dimensions identical for both materials... Then continue by listing all the activities that are required to build each of the buildings. Start at the foundation and continue all the way to the roof...

For each activity, list all of the resources (materials, labor, equipment, etc.) that are required to complete it. Then take the resource list and make a list of the components of each resource. Example: If wooden roof trusses must be hauled from a distant location, the components of the wooden trusses would include not only the lumber and other materials required for the trusses and the energy required to fabricate them, but also the transportation of the trusses to the project site. Keep working at this until all resources have been broken down into common constituent components and all of the components have been expressed in units that can be converted into "ecological footprint" units. Then add them all up and make your contrast and comparison study. The use of a computer and MicroSoft Excel - or a similar spreadsheet program would greatly facilitate the bookkeeping required for this study. I would like to know more about your definition of "ecological footprint" and how you finally decide to do the study. After that, if I can help you by looking at your results and expressing an opinion, I'd be glad to...

Q: Can you suggest how I might go about researching historical aspects of existing rammed earth buildings? I am working on a project that is requiring an architectural survey of a rammed adobe home built on the outskirts of Colorado Springs, CO in the early 1930's - which created quite a stir at the time. Were there general blueprints for the builder(s) to abide by?

A: I'm glad to hear of your interest in rammed earth building. However, I'm not much of a historian. This is probably going to be a difficult research project. Anyone who was actually around and old enough to remember at the time the building was built would be in their 80's or older... Your work will be like that of a police detective trying to solve an old crime. What you need is a few clues to start you in the right direction - then your work should get easier.

How did your hear about this building??? Who told you or where did you read about it...?? Is the building still standing...?? (It might be - rammed earth can last a long time - a good example would be parts of the Great Wall of China) If it was built on the outskirts of Colorado Springs in the 1930's that probably means it's darn near downtown by now...!! These are all avenues that should be explored.

I'd suggest that you start by using the same techniques historical researchers use for almost any project. I'd start by getting the legal description and/or the address of the property where it is/was located. Then I'd go to the El Paso County courthouse and/or the local title insurance companies and look through their records for the property. Either the county clerk or the county assessor might have something. Also check with the City and/or County building department... They might have some records. I'd also take a look in the morgue of the local newspaper. Hopefully it - or a predecessor paper - has been around that long. Perhaps you'll find some reference to such a building there. With luck their old issues will be on microfilm.

You should also check with the local historical society. A town as big as Colorado Springs almost certainly has one of those. If they don't have any direct information, maybe they could put you in touch with some old-timers who might recollect something about it. The local public library might also be a good place to spend some time. You should also look for people who have written books or articles about the history of Colorado Springs. These folks do a lot more research than they actually use for their published work.

Q: We are looking to buy a rammed earth home in Northern California, specifically in Colfax which is about 50 miles North of Sacramento. We have been told that the home was built in 1909. It seems to be in good shape, it is built on a concrete foundation, but the foundation is below grade. Can you share any information you have about early Rammed earth building in California? Who may have done it, what methods may have been used, your opinion on purchasing the home, what we should look for?

A: I know a few things about it, but I'm no expert on early California rammed earth projects. My suggestion to you is to get in touch with David Easton at www.rammedearthworks.com. David is a California architect who has done a great deal of research and construction work with rammed earth. He might be a MUCH better source of information than I would be.

Q: I have been reading Earth Construction by Hugo Houben and Hubert Guillaud. The book discusses a rammed earth method in which the earth is vibrated rather than pounded. Supposedly GHK in Kassel, Germany produces a vibration machine, but I cannot find any information about it. I would appreciate any help you can provide in helping me find one of these machines. Also any help you can provide in helping me find a pneumatic rammer suited for rammed earth construction would also be most appreciated.

As with almost anything, there are a number of different ways to "skin the cat" as far as rammed earth compaction is concerned.  Here are some random thoughts on the subject:

1)  On a lot of projects, there are electrical conduits, pipes, etc. running through the rammed earth.  These require hand compaction around them...

2)  The pneumatic rammers are very hard to handle.  Using one for a few hours will wear even a seasoned construction worker down.  On my own project, we found that it was easier to ram the earth by hand than to use the pneumatic rammers...

3)  If you are going to try to vibrate the rammed earth mix, it will have to have a higher % water and maybe more sand and cement than a mix designed for compaction.  What I would try to do, I think, would be to mix it to about the same consistency as a portland concrete mix with about a 4-6" slump, then place it in the forms and use a concrete vibrator on it.  You can get electric concrete vibrators at Harbor Freight ( www.harborfreight.com )  

4) Pneumatic tools of all kinds can be purchased at Michigan Pneumatic Tools ( www.michiganpneumatic.com ).  I bought my rammer used from them.  You will find that tools like this are quite expensive. 

Q: I am trying to replace a railroad tie retaining wall that is about 20 feet long and 8 feet high at it's highest point. I would like to use rammed earth tires to replace it however I am having a hard time finding any information on landscaping with tires. I guess my question is, must a ram them full of earth as if I were building a house wall or could I use gravel or a gravel/dirt mix and pack them less vigorously? Although I am no stranger to hard work, I weigh 110 pounds and the thought of packing them so full of dirt is slightly daunting. Just filling them with gravel and then going over it with the maul seems right up my alley. Any thoughts?

A: Pounding tires would be a daunting task for a 110 lb person...  The sledge hammer by itself is a significant part of that weight...!! I think you would be OK using small to medium size gravel in lieu of finer-grained soils as long as you did enough compaction to make sure that the tires were completely full of the material with no voids or empty spots.

Start by excavating level space for the bottom row of tires, place the tires, fill them with gravel, and compact with a hand tamper.  Then anchor the bottom row to the underlying soil with 24" rebar stakes.  Then fill level behind the row with local soil and compact it with the tamper.  Add a bit of water as necessary to get good compaction.  Then place the next row of tires.  Be sure to set them back a couple of inches - or a bit more - from the front of the first row and repeat the process until the wall is as high as it needs to be.  Be sure to backfill each row as you go - and to anchor at least every other row with rebar stakes.  You could utilize recycled material for the stakes - like 1/2" pipe, old steel fence posts, etc.  Utilize a consistent size of tire within each row if you can. 20 feet wide might not be wide enough for an 8 foot high wall.  If necessary, extend the wall as far as necessary.

Q: I'm currently doing some research in rammed earth. The more I learn about it, the more interested I become in getting involved with 'green architecture' or just being able to design buildings that are more environmentally friendly. So what are some job avenues that I could look into?

A: I'd suggest that you look into doing an internship with an architectural design firm that is involved in rammed earth or some other type of green building.  I'd start by writing letters to firms that are known to be in the business - like David Easton's in California - and following up with phone calls, etc.  Always ask for referrals - as a particular firm might not have room for an intern right now, but they probably know of other firms that are in the same business...

Q: The north east side of a 2 year old rammed earth house is showing  extensive crumbling and deterioration. The contractor who built it (it was his first rammed earth house) says that the solution would be to seal that side with Elmer's glue by hand.  We are upset and not sure what to do at this point.

A: I've never heard of using Elmer's glue on a crumbling face.  Don't know why it wouldn't work - the only way to know for sure is to try it and see.  I do know that linseed oil - or clear liquid concrete sealer applied in repeated coats with a sprayer works fairly well...  I think I'd try those things first and save the Elmer's for a last resort.

Q: I am an architecture student at the Kwame Nkrumah University of Science and Technology and I would like to know the cost per metre squared of a wall for a rammed earth building. I would like to compare this to the cost per metre squared for a masonry wall or concrete block wall of the same area. I would like to know if it would be cheaper when used in a developing country like Ghana. This would really help me in a very important project I'm undertaking.

A: I really can't help you with costs...  Here in the U.S. the costs of manpower, equipment, and materials are likely very different than in Ghana...  So - - the methods used to build rammed earth walls - and the costs would be quite different as well...I can say this...  If you can find good sandy-clay adobe soil that requires little if any cement for stabilization - and you can provide a good roof to protect it from moisture, then the cost is likely to be very low in a developing country situation...  David Easton makes some comments about this in his book, The Rammed Earth House, which I would strongly suggest you consult.

C: I am currently building a rammed earth house in Albuquerque, NM. My rammed earth wall contractor is Huston Rammed Earth from Edgewood, New Mexico. He is a 3rd generation rammed earth builder with a very "high tech" of building as far as rammed earth goes. I saw some inquiries on your site about builders in the southwest and he is one of the best.

Q: We are considering building a rammed earth home on the big island of Hawaii. We have a soil that is volcanic ash. It looks like clay but it doesn't act like clay. Could this work and what ratios of this soil to cement and aggregate should be used?

A: (Kelly) I might offer this bit of information from someone who is building an earthbag dome home in Hawaii using the ash. He is using close to 10% mix of cement, partly because of the high humidity...

Q: It seems like geopolymer walls that turn to actual stone would surpass rammed earth (and earthbag) in terms of strength and durability. It would be great to get your input on this. Here's the link to my recent blog post on geopolymer and how some scientists believe it was used on part of the great pyramids of Giza.

A: Rammed earth is in essence man made stone that is made using aggregate with binders and water. The proposed pyramid blocks are similar to cement in that they would be poured as a liquid. but to me it seems that all 3 methods are similar in their final form. Strength would vary due to several factors, mix quality, curing procedures and strength of their weakest particles. Each method has pros and cons depending on a person's requirements. Rammed earth offers a feeling quality and beauty aspect above these other materials.

Q:  I am looking to construct a wood drying kiln of rammed earth for the structural strength, and insulative properties to maintain temperature for longer periods of time, and later in each cycle raise internal temperature to 160 degrees to kill off any insects in the beams or lumber. I live in the northeastern corner of Alabama, and have a red clay subsoil. I have conducted jar test, and consulted with a guy that looked at my sample and says I have a 50% clay content, and a 50% sand content. After reading some of your Q&As I now question whether I have silt rather than clay.

A: You can do a jar and water test, but also you can just send your mix to a geotech lab and ask for a particle distribution test. That will tell you what it's made of and what % of each is in the mix. You will need to add clean aggregate to your mix, 3/4" and smaller. The clay content would be 10-15% optimally when you have finished blending. 

Q: (Kelly) I would be interested in your take on the possibility of prefabricated earthen walls.

A: I don't see a future in prefab RE walls, I have made some huge ones ( 18' tall) and also consulted with a experienced RE builder who shared the challenges of this idea from experience. The real solution is to improve cast on site RE walls, there is a lot that can be done to improve efficiency and lower cost.

Q: If I want to build a relatively high rammed earth structure (4 storeys) what sort of dimensions am I looking at for the walls? Is it also possible to have screw piles as a foundation for such a structure? I should add that the soil is clay dominated and it rains/snows often so should I presume that cement stabilization is a must?

A: You can make a  building 4 storeys tall with stabilized rammed earth (SRE) , the wall thickness can be 2' / 60 cm . Cement stabilization is best for your application for long term durability and structural strength. For footing design you should have a geotechenmical engineer analyze your ground conditions and have a structural engineer design the foundation accordingly. It is important to respect the damage that high clay soil can do when it freezes under a foundation.

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