Uses for 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: We are wanting to construct a partially in-ground home in northwest Florida. Our land is on a slope and not in any flood zones. Our current conventional brick house has survived without any flooding through the multiple hurricanes and tropical storms that have crossed over this area. Would rammed earth walls be feasible in-ground or partially in-ground? Would you need any cement or separation from the dirt around the home and the rammed earth walls?

A: Stabilized rammed earth walls are certainly feasible for below grade applications. You will need to place the walls on a concrete footing ( no stem wall is necessary). You would treat the rammed earth like a concrete wall and need to damp proof it and also use the proper drainage of course. Stabilized rammed earth will maintain it's structural integrity even if totally submerged in water.

Q: What is the main point of rammed earth?

A: (Leonard Jones) In my opinion, the point of rammed earth is to build earthen walls with local, vernacular material. The walls can be used as fences or as landscaping features, but primarily they are used as walls for homes and other buildings. Earth is available nearly everywhere. Much of it is suitable for building rammed earth walls as is. In other cases, stabilizing components like Portland Cement or asphalt emulsion must be added. If properly built, rammed earth walls will be strong and durable. Rammed earth buildings and structures in parts of Europe, Africa, and Asia have stood for centuries. Much of the Great Wall of China is rammed earth. In third-world countries, where low-cost labor is available, labor-intensive methods, and improvised low-cost forming systems can be used to build rammed earth walls. In Western countries, where labor is expensive, mechanical equipment can be utilized along with prefabricated metal or site-built wooden forms to achieve the same objective. A variety of “in-between” options exist, providing flexibility to meet nearly any situation.

An advantage of rammed earth (and other earth building methods) is that a great deal of “thermal mass” goes into the building. If combined with south-facing glass, proper shading, and tight construction, the result can be a home that will provide much, if not all, of its own heating and cooling. Like other earth building methods, rammed earth has its own characteristics, advantages, and disadvantages. If you are considering a project, consider the issue of labor vs. equipment and come up with a plan. Before you commit, be sure to take a look at other methods; compare and contrast them: · Tire wall (earthship) · Adobe Blocks · Pressed Earth Blocks · Cob · Earthbags

If you want to know more about rammed earth construction, I strongly suggest that you read The Rammed Earth House by David Wright, a California architect who has designed and built many rammed earth homes

Q: 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?

A: (Bruce King) There are no reliable tests as such; you just need to build some sample structures (eg benches), and whack them about after a few months to see how strong they are. Without either clay, lime, or cement, however, you're not likely to get much cohesion ( =strength = durability).

Q: Using cast earth (cement earth mix) do you think it would be ok for under ground use? What about dome styles? Also any good ideas for waterproofing cheap maybe a latex paint and plastic?

A: (Bruce King) "Cast Earth" as the name is patented, uses calcined gypsum (not cement) for stabilization, and is absolutely not good for sub-grade use. Not too great above grade, for that matter. Soil cement (CEMENT EARTH MIX, as you put it), has many possibilities, but you'd have to play around with mixes and do experimental structures. It is much more permeable to water than concrete, so sub-grade and dome structures will be vulnerable. (Earthbag domes are particularly hard to seal; ones in California have received multiple layers of expensive waterproofing systems and still leak.)

Q: We live in South Australia and are considering building a rammed earth home. Do you know if it is feasible to also have an earth floor instead of one from concrete? When I say 'earth' I mean, can a solid, uncrackable, easily swept and kept clean floor be made from rammed or pounded earth? What about for a bathroom/laundry?

A: (Bruce King) Yes, a solid, uncrackable, easily swept floor can be made from rammed or pounded earth; it is an old art/science developed independently in various parts of the world. It also takes a lot of work, and especially patience.

Q: I'm planning to make a retaining wall about five foot tall to level off my yard. Is the rammed earth method good for this and would I need to have a foundation?

A: (Bruce King) Yes and yes.

Q: I am looking for information or making a rammed earth floor but I have been unsuccessful.

A: (Dan Chiras) Rammed earth floors are a great alternative to poured adobe floors. They dry a lot faster and, will probably crack less. They're easier to make as well. I'm no expert on rammed earth floors; I have only helped make one floor (very tiny floor) in a small workshop in New Mexico. That workshop was led by Frank Meyer from Austin, Texas. I'd suggest you contact him at thangmakerATaol.com.

Q: I am building an addition on my horse barn to be used as a wood working shop, and have considered a rammed earth/linseed oil finished floor as an alternative to concrete. Can't find any specifics on how to proceed. Any ideas?

A: (Kelly) Rammed earth and adobe floors can be beautiful and quite durable, but for a shop floor, they would not be my first choice do to the vulnerability to damage from shop use...I would stick with concrete.

Q: Can you build the basement foundation out of all Rammed Earth? P.S I am a student at a technical school and we are designing a greenhouse, I am designing my house out of straw.

A:(Leonard Jones)It would be inadvisable to build a basement foundation out of rammed earth unless it was mixed with enough portland cement to make it the effective equivalent of concrete. Otherwise it will probably not stand up to moisture it is likely to encounter. And, if you're going to use that much portland cement, you might just as well mix concrete and gain the advantages in strength and durability that come with it. There are a number of other foundation building methods that you may want to consider instead. These include the rubble-trench foundation, rammed tire foundation, and urbanite (used concrete chunk) foundation. It would be advisable to consult the best available strawbale reference and to follow the guidance therein.

Q: I am designing a model solar house in rural NW China, with rammed earth walls. I am trying to stay as similar as possible to local building methods. They often have earth floors (not treated at all), but complain of dust as a problem. It seems linseed oil is a common treatment for earth floors from your website, but I'm afraid it won't be appropriate for us, because of it's flammability. Locals cook and heat using stoves w/ an open firebox, ... this would be dangerous, right? Because we want the floors to absorb solar heat during the day, the floor treatment also needs to be able to withstand high temps (thus wax is not so good, right?). Would oil in earth floors also melt and make the floor slippery? Do you have any other suggestions of what we could use?

A: (Leonard Jones) I'm not sure that using linseed oil would be a problem. It soaks right into an earthen floor and over a period of a few weeks to a few months, the lighter, more flammable volatiles evaporate out of it. If I were you, I'd do a test, though... Build a small section of earthen floor near your stove, treat it with linseed oil and see how it comes out... After it cures for a few weeks, try to set it on fire... If it starts burning easily, then don't use it... If you need to stabilize the floor, you might try mixing some portland cement into the top couple of inches, then leveling it off, then adding some water, then compacting it before it cures. Lime might work also, depending on the soil.

Q: As a student of industrial design, I am proposing a thesis for alternatives to the playgrounds that are currently being built in Toronto, Canada (mostly plastic, and metal, and built on flat, pre-landscaped parks). I'm wondering if rammed earth could be a potential alternative, and where the best information could be found on rammed earth structures other than homes?

A: (Leonard Jones) I'm not sure that "ordinary" rammed earth as would be used for a house would do the trick on a playground...  All those little feet would provide a lot of abuse and abrasion that house walls never see... What might work would be to increase the the Portland cement ratio from ~1/27 to around 2or3/27.   This would still be less cement than is used in concrete (4-5/27), but it would have more resistance to abuse and abrasion... A few simple experiments might tell you what you need to know...

Q: I have a client who is interested in a fireplace face made from "rammed earth" .. I am looking for a qualified subcontractor if there is such a person. The project is in southern California.

A: (Leonard Jones) I'm glad to hear of your client's interest in rammed earth. However, I'm not sure that the application the client has in mind is a good one.  I don't know if rammed earth would stand up to the significant thermal expansion and contraction that it might receive as part of a fireplace.

Q: I am an interior design student and am focusing on environmentally sustainable products for a private dining club design. Would a rammed earth floor practical for commercial use in the Southern California area - taking into consideration smoothness (for ADA reasons), and durability (spills and drops from a restaurant)?

A: (Leonard Jones) I believe that, with a little work, it would be possible to spread and compact a floor of rammed earth soil mix (sand, clay, and Portland cement as a stabilizer) to a degree of smoothness that would be equal to a concrete floor.  With enough Portland cement, it would be very durable, physically, and would stand up well to wear and tear.

However, your question about spills and drops is a good one.  I'm not sure if a rammed earth floor could be sealed up well enough to avoid soaking up spills (especially greasy spills).  Most rammed earth floors are sealed with boiled linseed oil - I'm not sure if it is up to the task of keeping a restaurant floor up to the sanitary standards demanded by local authorities.  Perhaps other sealants would do a better job. 

The only way I know to find out about this issue would be construct some sections of rammed earth floor, seal them, and test to see how well they hold up to spills...

Q: The rammed earth constructions and natural building materials sound great for a sustainable development. Being an architect based in urban India where the density of population demands the construction of apartment buildings of at least 4 to 5 stories, how can these principles be adopted for these construction? What is the sustainable way out?

A: (Leonard Jones) I'm sitting here in downtown Denver right now, looking out a 9th floor window at the cityscape and thinking about sustainability - which seems a bit peculiar and counter-intuitive to me.  But sustainability is a word that can be interpreted in many ways - depending on where you happen to be standing when you look at it...

If your view of sustainability is that the local culture and architecture must be self-sustaining (or nearly so) in terms of food, water, shelter, energy, and other necessities of life, then it is hard to picture urban India (or urban anywhere) as sustainable.  High density urban cultures are extremely dependent on the export of products and/or services for money and the exchange of money for food, energy, communications, transportation, etc from outside the immediate area.  If something happens to break a vital link in this cycle of exchange for a significant period of time, then the culture will change or perhaps collapse back to an agricultural village level.  (See Jared Diamond's recent book, "Collapse" for an analysis of factors that can cause cultures to fail.)

However, if your view of sustainability is that these things, particularly shelter, should be provided in a way that provides for minimal or best use of scarce resources during initial construction AND long term use, then perhaps something can be done.  Start by stepping "outside the box" and tossing all the "normal" constraints out the window.  Then treat the design as if it were an analysis problem from your first year or two of architecture school.  There are some interesting things you could do to enhance sustainability, including - but not limited to - the following:

1)  Life Cycle Costing - consider the energy, water, money, and other resources that will be consumed during the entire life of the project.  There is ALWAYS a trade-off between initial cost and long term cost.  Can you push the trade-off in a more sustainable long-term direction?? 

2)  Embedded Energy Budgeting - Energy cost has become a much larger factor in manufacture of construction materials in the last year.  In my opinion, energy costs will continue to rise for the foreseeable future.  It would be interesting and instructive to add up all of the energy embedded in the construction materials and methods along with the long-term energy use for each construction alternative and compare them one to the other.

3)  Material and Energy Balance - Another interesting analysis would be to compare the materials and energy entering the proposed structure with those leaving.  We know that, in the long term, what comes in must equal what goes out...  Food comes in, human waste and garbage go out, etc. etc.  What waste products are there???  Is there some way that useful work or material or money could be extracted for the benefit of the occupants or the owners...??

I'm not sure that rammed earth, as traditionally utilized, would be of much use in your proposed multi-story building.  Unless you add a lot of portland cement (which adds cost and embedded energy) rammed earth is not particularly strong - adequate for a story or two, but not for 5 or 6...   It might be instructive to study existing multi-story earthen buildings...  The largest such building in North America is probably the Taos Pueblo, which is also the longest-standing continuously occupied structure in the United States. 

Q: The information that even 2 storied structures are feasible with earth constructions is quite useful. What would be the roof structure in this case, reinforced concrete?

A:(Leonard Jones) Reinforced concrete is typically only used in large and high rise commercial, industrial, and/or multi-family residential buildings here...  Most one or two story buildings get wooden or metal truss roofs or engineered wood (trus-joist) roofs.  There would be nothing in particular wrong with using reinforced concrete for a roof...  It is all a matter of cost and structural requirements. Also, I would suggest that you obtain and read  David Easton's book,"The Rammed Earth House"  It is one of the very best books on the subject that I have myself read...

Q: I am a graduate student in Jerusalem, writing a seminar paper on Roman siege ramps used here in 70 A.D. The primary sources are not very specific as to how these ramps were built, but I suspect they may have used a rammed-earth variation. Do you have any ideas or references regarding this?

A: (Leonard Jones) I presume that you're talking about the siege at Masada...??  Certainly a singular historical event in that particular time and place - militarily and politically as well as engineering-wise... It's interesting to me as I'm not only the "rammed earth guy" at greenhomebuilding.com, I'm also an ex-US Army Combat Engineer Officer.  The Roman Army at the time had officers who were trained engineers - who were in charge of river crossings, seigeworks, etc..  There were no regular engineering units, as the great majority of the work was manual labor, which was done by ordinary Roman soldiers or by paid or conscripted locals. 

Interestingly, the title used to describe these engineering officers was the Latin word "Pontifex."  (Pont = bridge and fex = builder)  This title is the same as that used to describe the Roman Catholic Pope, who is known as "Pontifex Maximus."  A large part of his job is to build bridges of understanding and break down barriers between groups of people and between people and God... 

Back to Masada...The ramp was probably built for a couple of reasons...  after the Jewish (rebels or heros) depending on which side of the struggle one was on) invested the mountaintop and established defenses on the approaches, it would have been effectively impossible for the Romas to make a direct assault on the mountain.  Also, Masada is sufficiently tall that the siege engines (catapults, etc.) could not reach to the top.  So a ramp had to be built. 

My educated guess is that the siege ramp at Masada was not a deliberate rammed earth effort where earth was placed and deliberately compacted in layers...  The engineer in charge of that siege probably used geometry to figure out how high the steep mountain was.  Then he would have calculated how steep the ramp could or should be and determined the starting point - which would be quite a ways back from the mountain.  Then he would have directed the workers to start dumping earth to build the ramp at that point.  Compaction would have been incidental to the process of dumping more earth and continuing the ramp toward the mountain.

The ramp could have been started at the foot of the mountain, but then the Jews on top would have been able to roll rocks, throw spears, and shoot arrows down on the workers.  This would have resulted in a lot of casualties and delays...  Starting at a distance meant that by the time the ramp approached the mountaintop, it would be nearly as high as the mountain - taking away any advantage that gravity might provide. 

Of course, history tells the rest of the story...  The siege took a long time, but the ramp was eventually completed.  The Romans made their final assault, only to find that the occupants had committed group suicide.

C: About rammed earth floors. They are indeed a viable and sturdy floor; easily maintained. Basically you use no cement at all. Ram the earth floor like you would the wall, screeing the floor for leveling. You use a mix of 3 to 1 linseed oil and paint thinner to seal the floor. The first 2 applications should be 3 paint thinner to 1 linseed. The last should ne 3 linseed to 1 paint thinner. Leave the house open to the air for one week if possible. It WILL resist all spills and sweeps well. You can even mop it if you want to. Every 4 years, apply a 3 to 1 to maintain. Our neighbor built his strawbale house and put in this flooring. It has been 7 years and he has yet to treat it again, and it is still beautiful.

Q: Do you know of a book that details the building of a rammed earth foundation ?

A: (Kelly) Rammed earth is not generally recommended for a foundation; I have never seen any information suggesting that it be used this way. You are much better off with a rubble trench, earthbag, stone or concrete foundation.

Q: I'm considering constructing a timber house with a rammed earth perimeter foundation (in place of stumps) to rest the bearers on, with timber used for internal stumps. Maximum height is 1.8m and preferably 0.3m thick. Would this be viable? If you get quite a bit of rain there, I wouldn't recommend rammed earth for a foundation.  The amount of cement required to protect it from water damage might easily make it more expensive than concrete.  Perhaps you should consider a rubble trench foundation or maybe urbanite, if it's available. However, if there are quite a few other rammed earth houses in the area, I'd strongly suggest that you talk to their owners to see if any have used the technique you are proposing.  If so, find out how well it's holding up and what they did to make it work.  If not, using the technique will be at your own risk.  The cost (not just $$ but otherwise as well) of pioneering a new construction method can be quite high.  

Q: I am a 2nd year student at CEPT University, Ahmedabad, India. I am planning to build a basketball court out of rammed earth; dividing the court into a number of parts each being 14 ft by 10 ft. My question is whether it is appropriate to have pieces of such a size in the form of slab(when they are laid for making the court) or should the pieces be smaller? Basically wanted to know which would the best way to make a horizontal wall of a size of that of a basketball court.

A: (Leonard Jones) I think this is a decidedly bad idea.The pounding of basketballs and feet will quickly turn this court into a dusty mess..

Q: I live in the mountains of central Mexico and am considering a rammed earth house. 99.9% of homes here are adobe or brick. I'm looking at a Santa Fe style plan but I'm concerned about the summer rains we get here [every afternoon during summer, like clockwork]. I don't want to detract from the house with huge eaves etc. Suggestions? Also, in the area I want to put the house, there can be a lot of water during the rainy season. I would of course elevate the foundation, but I was considering a rammed earth foundation as well. Causes for concern?

A:(Leonard Jones) Yes, there are concerns.  The rammed earth foundation could erode right out from under your building. If you want to do this, put in an elevated foundation with rammed earth that has a high percentage of "stabilizer" - either Portland Cement or asphalt emulsion.  "Normal" rammed earth has 3-4 % Cement.  Concrete has 15-20% cement.  You would want to use more than 3-4 but less than 15-20.  I'd suggest building a form and making some test foundation sections.  Take some photos before the rainy season and afterwards.  Pick a mix that minimizes the erosion.   Also, take a look at the adobe houses in the area and take note of what they have done for erosion prevention.

Q: I am interested in using rammed earth, but in a different way. I would like to build a mold using the existing exterior wall of my house as one side of the mold and use rammed earth. Should I prepare the existing wall in any particular way, or would this method not be recommended for any reason. I think this would provide the extra thermal envelope and protection, and, though labor intensive would be much cheaper than siding and more beautiful. Have you ever seen or heard of this being done?

A: (Kelly) No, I have not heard of anyone doing this before. I have several thoughts about what you propose. Forms for rammed earth need to be exceptionally rigid and sturdy to withstand the pressure of all that heavy soil and the stress of compaction, so your wall would need to be able to withstand this. Usually, earth is rammed in a series of "lifts," with a fairly short form that is simply lifted up after the layer below has solidified sufficiently. In your situation you would have to figure out how to physically ram the earth against an existing wall, and brace the opposite part of the form at the same time. My last thought is that if it is improved insulation that you are looking for, rammed earth might not be the best solution, since it is really a thermal mass material that is ideally placed inside a wall...unless you then insulated the rammed earth on the outside with a layer of insulation as is commonly done in many climates.

Q: I am considering putting a chimney in the back of my house which was added on and only one level with a roof that slopes approximately 10 degrees. The added section includes a kitchen about 10 feet wide and a small workroom on the end with a concrete floor. I would like to build a chimney on that floor running up through the roof, probably around ten feet high with enough extension above the roof to meet code. I think rammed earth with about 10 inch thick walls would be excellent for the chimney and either a pre-made clay liner or perhaps make my own liner with clay. Do you have any information on using rammed earth for chimneys? I am thinking adding extra cement to the mix might be a good idea to give it a little extra compressive strength and minimize the chance of it possibly falling apart from being bumped or hit (the location is in my workshop so I do a lot of work in there)

A: (Quentin Wilson) NM only allows firebrick built fireboxes and factory clay flue liners. These days, I favor metal insulated or double walled flues. They do not cool down the flue gasses and there is far less build up of creosote in the chimney. Aside from that, a clay tile flue with RE surrounding it would be a great way to extract and store heat that is otherwise lost up the chimney. Just plan to be more vigilant, proactive and preventive maintenance minded regarding the flue.

Q: I would like to put a basement under my rammed earth kitchen - this is hypothetical as I'm studying architecture. What are the options apart from concrete? Could I build retaining walls with earth packed tyres and so on...the basement is a food store.

A: You can use stabilized rammed earth for basement walls if properly designed. The same considerations need to be taken as with concrete walls for basements for both structural and building envelope issues. I specialize in rammed earth walls that have no tires in them and do not advocate using tires in any way.

By stabilized do you mean there is a higher percentage of concrete mixed in or are the walls reinforced with rebar?

Stabilized rammed earth uses lime or cement to prevent the clay particles from re-absorbing water and increases bonding of the material. This will give the walls superior strength and durability compared to unstabilized rammed earth. Reinforcing steel is a matter of choice; we always use it in our projects.

Q: I intend to build a privacy wall in my back yard. I wish to make it three sides, with the open side facing my house. I am debating giving it a roof and making it a shed because I don't have the resources to make any kind of sophisticated roof. My question is as follows: is it possible to use rammed earth as a roof, or would it crack under its own weight? I could include some columns if necessary.

A: It is technically possible to make the roof with rammed earth. But I highly advise against it even for an experienced builder. Without lots of experience in rammed earth and extensive forming experience chances are it will not work. I don't want to take the time to list all of the problems that are possible but trust my knowledge in this material and construction when I say find a light weight solution that is easy to implement.

Q: I love rammed earth so much, I want to use it everywhere... including the shower. Is there a clear sealant or epoxy or something that could be applied over the rammed earth to protect it from water damage? I would use an overhead "rain" style shower so that the only real damage would be backsplash.

A: The sealer that we use is RamSeal it works fantastic. The key with sealing is to follow the instructions so your wall will look great after you are done.

Q: I am considering building a patio and pathways using large (18" square) rammed earth "pavers". I'd appreciate your input on what ratio of sand to cement would hold up best without the use of cement for high traffic, weather exposed locations. What thickness would be necessary to prevent cracking/breaking? Would they benefit from the addition of small gravel to the mix? I wonder if gravel near the surface would eventually work its way loose and leave pits in the surface? Any other ideas or suggestions would be much appreciated.

A: The best stabilized RE mix is approximately 75% gravel and sand 15% clay and 10% cement. Pavers are not the best application for RE but if you like the look then that's fine. I would suggest a surface treatment on the top of the paver.
I would not even attempt pavers without cement, the traffic and weather will be hard on it. Expansion and contraction of clay due to water and heat, combined with wear on an unstabilized mix would be undesirable. Unstabilized RE would have loose stones and sand that would leave pits. Once RE is stabilized with cement, then it is very durable, similar to concrete.

Q: I am working on 14x18 addition that is framed on grade, meaning the floor is at ground level. I don't want to poor a slab base, I'd rather have the earth directly beneath my feet, but also don't want an earthen floor. Is it possible to lay ceramic tile over a rammed earth base? I am in a fairly low area so I think I'll need a moisture barrier, but I'm unsure if I need to put down a grout base. I'd like to perhaps place the tile directly on grade and maybe use a flexible grout between the tiles. Does this sound feasible? Is there anything I should watch out for?

A: Yes, you can lay tile over a rammed earth base. For sure use a moisture barrier under the rammed earth, not on top as you need to adhere your tile. If the rammed earth is unstabilized you run the risk of water causing the clay to swell and that would crack your tiles or grout. I suggest stabilizing the rammed earth with cement even if only 5% of the mix, this will prevent any expansion. Yes, put down a scratch coat down so you have an even surface and good bonding for the tiles.

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