Adobe Floors

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: I live in the S.E. corner of British Columbia, Canada, and am currently working on a square log dove tail house with a timber frame roof system. I 've been looking into earth floors, and have come up short with enough info to try one on this project. I'm very impressed with Paul and Talmath's work and their write up about earth/abode floors. I would be interested in any other sources of info for proceeding with an abode floor on this project. I would like to do 1 1/2" layer over radiant tubes on top of an OSB subfloor. Anybody doing this?

A: Adobe works just fine for radiant. That OSB floor needs to be very rigid so that there is little flexing under the adobe. It also needs to be very waterproof since the adobe floor takes some time to dry out. I would recommend a minimum of two inches adobe. That gets heavy.

A: (Kelly) There is not a lot out there about how to actually make earthen/adobe floors. I did notice that there is a chapter in this book: Earthbag Building : The Tools, Tricks and Techniques by Kaki Hunter, Donald Kiffmeyer, 2004. Talmath has often done adobe floors over radiant tubing, and this works well, since the heat can used to help cure the adobe faster, and then the adobe becomes good thermal mass for the floor. Using OSB as a subfloor with adobe sounds risky to me, since this material will decompose when wet...

R: I'll be putting 15lbs roofing felt as a bond breaker between the OSB and the abode, so moisture shouldn't be a problem, also considering  using wire mesh over the radiant tubes, well see......

A: (Kelly) I have never seen wire mesh used this way with adobe floors, so it probably isn't necessary. I have seen it used under radiant tubes embedded in concrete to hold the tubes in place when it is poured... Will the OSB be able to breathe from below? If it can't, then any moisture that does manage to seep between the courses of felt and find its way to the OSB will never be able to exit. Solid plastic sheeting might be safer, and also be a better radon barrier, if this is an issue.

Q: We are installing an adobe floor on a house in Huntington VT and are wondering about green products used for sealing adobe floors?

A: Boiled linseed oil is my choice. Put on one or two coats without thinning to load up the pores. After 20 minutes wipe up any oil on the surface or it will become gummy. A day between coats is good. Thin the following coat or two 50% or less with turpentine or citric oil thinner to help make sure that the linseed oil hardens. It's an oxidation reaction. Again, mop up any residue on the surface after 20 minutes. Linseed is the hero of all the firefighters training movies because it combusts spontaneously better than anything else. So put any rags in a sealed container or in a bucket of water.

Q: I will be laying fired adobe as patio pavers. I am wondering how they should be laid. Base materials? Depth? Sand? Depth? We are in metro Phoenix. 7" rain per year +-

A: It is best to have 2- to 4-inches of sand under the pavers. The sand can be right on the existing soil if it is firm and has never been excavated. Otherwise, base course well tamped is in order. 4-inches of base course, then a geo cloth is useful to keep the sand from filtering down into the base course. Then the sand, then the bricks. I would say skip the use of grout and place the adobes as close together as possible. That way rain can drain down between the adobes and percolate down into the ground. Rain that stays on the surface has more time to penetrate the top surface of the adobes. Some people sweep sand into the spaces between the bricks. It will go faster if you can level large areas of the sand and then just drop the adobes into place without having to level each one. If the adobes have much difference in thickness, this shortcut is not that helpful.

Q: I've been told to coat them with a turpentine / Linseed Oil mixture to also help keep moisture off.  Does it sound right as well?

A: I am not so sure that this is appropriate outdoors. If moisture gets into the adobes, then the turp/linseed surface keeps it from getting back out. In some cases the moisture may move up to the point where the turp/linseed begins and then break the connection between the raw and the treated adobe. I have definitely had this happen on a treated vertical wall surface.

C: I've laid some 3x8x16 fired adobe on a patio.  Because of thickness concerns I had to lay them in 1/2" sand.  Those little suckers were so sway-backed that it was barely thick enough.  A couple of brick have cracked as I tamped them.  Oops.  But boy do they look pretty. I think one inch is the minimum thickness I'd use again.

A: I agree. Swaybacks are hard to deal with. I have taken a vibrating plate tamper and run it over a brick on sand floor with a strip of half-inch plywood between the plate and the bricks. Once the machine gets up to speed it is as if it liquefies the sand and the low bricks float up and the high bricks are pressed down. It might work on the adobes and fill any voids under the swaybacks.

Q: Are adobe bricks stabilized with cement an appropriate material for patio and/or walkway pavers?

A: It is hard to know for sure. There are so many levels of stabilization. Pavers of any sort, brick, stone, concrete, adobe have to be able to resist almost all absorption of water in freezing weather or they spall apart after repeated freeze/thaw cycles. Adobe stabilized with cement and also asphalt has definitely been used successfully but each soil has its own characteristics and without good local experience or a testing lab, you are in an experimental mode.

Q: I'm thinking of constructing a small outdoor patio, 400 sq. feet out of adobe bricks I make myself. I live in Portland, Or. Is this feasible and do any of the books on your website address this type of project?

A: We would certainly like to see more adobe activity in Portland, Gary. The Oregon Historical Society has a photo of the concrete foundation of an adobe home in the Portland area. Pioneers coming in on the Oregon Trail used adobe along the trail until they got to the mountains. About 7 years ago adobe structures were put up in several neighborhoods mostly as places to sit near bus stops.

Using adobe bricks flat on the ground will take extra efforts. They should be stabilized (waterproofed) with emulsified asphalt which can be obtained from asphalt paving suppliers. For your application, I would think about 20 ounces per wheelbarrow would be a starting point. You might want to make a few test bricks and see how they hold up. If you don't like the idea of asphalt in the adobes there might be some other chemicals but my memory sags at the moment. Emulsified asphalt is the most common stabilizer used in the Southwest.

Additionally it would be good to lay the adobes on a bed of coarse sand or pea gravel to provide drainage below the bricks. In general people don't use adobe bricks as outside pavers but is has been done a few times.

I can't think of any books that address outdoor patios. Most stick with interior floors where the weather is not a consideration. Some of the best information on floors comes from Bill and Athena Steen bundled into their strawbale construction books.

Q: My husband and I are building a small (900ft2) hybrid type wood chip/light clay house in Quebec, Canada. I want to use as little concrete as possible but want a floor with good thermal mass. I would love a poured adobe floor but the labor, time, and timing involved are not practical for us. I am considering adobe brick/block and would like to make them myself. Is it a good idea to add a little cement for strength if they are being used as flooring? Do adobe bricks underfoot feel like concrete anyway? And how should they be finished/ sealed to get as smooth a floor as possible?

A: (Kelly) From my own experience, I would suggest stabilizing the adobe bricks with some Portland cement or emulsified asphalt for a floor, although this is not necessary. Earthen floors do not feel like concrete; they have much more earthy give to them. You can use linseed oil to finish them.

Q: I recently sealed our poured adobe floor with linseed oil and thinner (multiple coats begging with pure oil and progressing to higher percentages of thinner). The floor is now very well sealed, however, it is also a dust magnet. The slightest bit of dust from footprints of even slightly dusty feet or indoor shoes sticks to it and won't sweep off but needs to be mopped up. Is this effect common? Is there anything that can be done to help this, such as a final top coat of wax?

A: (Kelly) I lived for several years with an adobe floor that I poured in my house in Colorado, and I had the same experience that you describe. It was especially noticeable after I had re-oiled the floor (which I did about once a year). I found that after about week, when the oil had thoroughly hardened, the effect was much less noticeable. I did make sure to wipe away any excess oil that didn't sink into the floor after about half an hour, so that there was no build-up of oil "scum" on the surface.

I did not wax my floor, partly because I didn't like the way the wax left uneven whitish marks on the surface. I don't know whether wax would have improved the situation with dust. Every once in awhile I would take a damp mop to the floor to brighten the luster, but there was usually a dull, dusty appearance that I just got used to.

Q: How are your earthen floors holding up to doggy toenails?

A: (Kelly) I love our adobe floors. They do take some maintenance, especially around the inset flagstone, but the good news is that they can be repaired, unlike most flooring material. As you know we have two rambunctious dogs, one of whom is prone to scratch the floor with his nails. At first I thought this might be a problem, leaving permanent scratches. As it has turned out, a light mopping or wipe with an oiled rag will remove the marks.

Q: My wife and I are remodeling a 50's rancher with 2" t&g subfloor raised above grade. We would like an earthen floor, and wondered if there is any problem with applying it to the wooden subfloor? We have already run our hydronic heating attached below the subfloor, so that is done. We were considering wood, but it's expensive, and there is something about the earthen floor that really appeals to us. Someone described it as feeling like leather. Wow! that just sounds great.

A: (Kelly) Putting an earthen floor over an existing wooden subfloor could perhaps be done, but there would be some concerns. First of all, an earthen floor requires an absolutely solid, non-flexing base, or else it will likely crack in many places; this is hard to accomplish with a wooden floor, even if it is 2" thick. Second, an earthen floor is typically at least 3" to 4" thick, which means both a lot of weight (which must be born by the subfloor and foundation) and it will raise the level of the floor in the house by that much, likely interfering with doors and such. My third concern is that with hydronic heating you rely on the heat radiating upward. You have already compromised the efficiency of this type of heating system by placing the tubes beneath the wooden deck, since wood is an insulating material and will not readily pass the heat through. Earth is a much better thermal mass material than wood, but several inches of it may not pass enough of your heat into the room. Earthen floors with the tubes placed within work well, but I am not sure how well your situation would work. If it were me I would consider placing tiles over the subfloor, since these are a good conductor of heat, but are not too thick to have the other problems mentioned above.

Q: I was concerned that putting the radiant pipes under the floor was not efficient. This is the problem with working with people who want to move faster than I can fully research things. So, if I put, say, flagstone over the subfloor, that would still be a better conductor of heat, and storage of heat, than using a wood floor over the subfloor, even with the hydronics below the subfloor? This would keep the level of the floor closer to where it should be, too.

A: Yes, I would say that stone or tile over your subfloor would perform better than more wood. It will gather and hold the heat that rises through the wood and provide a more even temperature throughout the floor.

Q: I am wanting to build a tamped earth foundation for a guesthouse/art studio of 12' x 18'. I am unable to find a precise formula indicating an appropriate ratio of sand, clay, dirt, and water. I am planning on doing 6" of gravel, 6" of pumice, 3" of silty sand and soil mix, and then for floor layers--two layers of one inch each, clay soil, sand, chopped straw, water. It is just not clear for both the silty sand soil mix layer and the clay soil, sand, chopped straw, water layer, how much of each item to put in the mix?

A: 30/70 percent of clay/sand is best. Lots of soils work as they are or with a bit of clay or sand added. We have to experiment at each location. I would skip the pumice. It is very hygroscopic and will get damp and stay damp if it is in contact with surrounding soil. Any insulating value it has will be lost in a below grade situation. We used it as an under floor insulation at the Ghost Ranch Sundwellings in 1976. The buildings were heavily instrumented by Q-Dot at Los Alamos and they found the loss of insulative value in the pumice. (Editor's Note: If the pumice is kept dry with layers of plastic sheeting, it does fine as an insulating layer.)

As for the various layers, silt never contributes any value to a brick, mortar, plaster or floor. If it is there, use it, but if soil is available without it that will be the better choice. Back to 30/70 clay/sand. The straw is then not necessary but some like the texture and color it gives a floor. It does help control cracking if the clay content is over 30 percent.

As for water, just keep adding it till you get the consistency you like. Some folks like very stiff mud to spread and trowel out, some like it almost pourable. With 30/70 it all works. Since all soils are different, whether you are in Bali, Ethiopia or Berlin you just start out and experiment until it works. Two million Central Germans figured it out.

Q: I am designing a passive solar house in upstate NY. I need to top my concrete monolithic slab floor with another product that will effectively conduct heat and be softer on my husbands hips - he has had 2 hip surgeries. Can you suggest a product that will not compromise the efficiency of the concrete and be softer on some old hips?

A (Kelly): The first thing that comes to my mind is good old adobe. It is natural, holds and passes heat very nicely, and definitely is easier on the body. I lived with an adobe floor for several years, so I can personally attest to this. You can read an article that talks about this. Finding someone in your area who might be able to help install this might be the most difficult, but there are some directories of  green professional listed partway down my home page. Most products that are thermal mass that might be used for floor are not very resilient. Cork is nice, but it is also insulating.

Q: I live in India and would like to know which product in India is available to make an adobe surface waterproof. The floor is created with mud, straw, adobe clay, tile, cow dung, cake emulsion and cement grouting. Could suggest to guide?

A: I am not very familiar with the availability of materials in India. If you can find a fish oil emulsion, that might work. They use it in Chile with good results. It can be painted on but works better mixed into the adobe surfacing material before it is applied. Linseed oil and several other seed oils make adobe stronger and waterproof. They are painted on after the adobe material has thoroughly dried. Polyvinyl Acrylic the clear liquid used in many water based paints also works. Usually there is an elder person in most every village who has a recipe for something that works.

Q: I have read all I can get on earthen floors. Some say 6-12" of gravel "IF capillary rise of moisture is a problem". They don't say what to do if capillary rise is NOT a problem. Our soil is VERY well drained, it's rained into our foundation trenches several time and it drains fast. The excavator says jokingly (but not so much so) that our soil at the site is 90% rock and 10% dirt. I've read other places online that say they'd use 1 - 1/2 to 3" of gravel. Rohan Roy in Back Home magazine says their subfloor is "earth and gravel." I planned on using 6" of gravel because I wasn't sure if capillary rise was related to drainage and based on the Steen's method, didn't know what the alternative was. In my situation would 3" of gravel suffice?

A: My own home has poured adobe floors of 3-1/2" right on the existing dirt. I did no subfloor preparation. We have done others on 12" of gravel in very wet conditions of El Rito NM but the 12" was primarily to get the final floor up to the desired finish floor level. We have done adobe floors on 2" of sand followed by 2" of rigid polystyrene insulation followed by 2" more of sand. In your case 3" or no gravel at all should work just fine. Trust your excavator.

Q: I am considering making my woodshop floor a natural earthen floor. Do you have any experience with these floors and can you recommend a recipe or advice in such a choice? I am also interested in your opinion on 12"earth/straw infill walls compared to scoria earth bag infill walls with earth plasters applied inside and out?

A: (Kelly) I did make an earthen floor in part of the earthbag dome house I built about a decade ago. It held up pretty well, but it is vulnerable to scratches and gouges. For a workshop floor, I wouldn't advise this; there is just too much chance of abrasion. Many people who go to the trouble to make a nice adobe floor will have a shoes-off policy. You can see some of these floors at here. There is a recipe in this article if you want to try...

I'm not sure what the R-value of light straw/clay is, but my guess is that it is similar to bags of scoria. Either would give you a decently insulated wall. I am partial to the scoria since there is no chance of rot over time.

Q: I'm planning on building an adobe or rammed earth radiant floor. Is there a good book I can buy on this? Is rammed earth or Adobe more durable? I live in Kansas, near Kansas City; do you think the humidity will be a problem?

A: For a floor, humidity will not be a problem. An adobe floor will take longer to dry out especially if the walls and roof are already up. Rammed earth uses far less moisture and will be ready to walk on once the tamping is done.Both materials are actually strongest in an ambient humidity of 60%. Adobe will cure to 300psi compressive
strength and rammed earth walls easily get to 800 or even 1500psi. That might translate to greater scuff resistance but it is actually the finish on the top of the floor that determines that. We almost always used linseed oil. If you proceed with one of these floors, let me know and I can give you the detailed protocol for the use of linseed oil.

We have done several radiant heated adobe floors and they turn out fine. For either adobe or rammed earth it is essential to insulate underneath the floor especially where there might be more dampness in the earth than in the arid southwest states. Damp earth will move the heat right out of the floor and down never to return.

For adobe floors we pour over 2-inch extruded polystyrene rigid insulation. It should have a crush strength of at least 12-psi or better, 15-psi. Dow brand has that and at 2-inches is rated at R-11. The polystyrene should be placed on a flat, level bed of sand and that might be on top of a moisture barrier. The trick would be to follow
whatever guidelines there might be for a concrete pour in the KC area in terms of type and placement of a moisture barrier and then do that with the adobe or RE floor. If the radiant tubing is 1/2 or 3/4-inch PEX, we buy hog fencing panels to put on top of the insulation to form a flat, sturdy grid to which the PEX can be attached with cable ties. More often, 6x6 10/10 remesh is used but it is so annoying to unroll and try to flatten that the hog fence panels seems like a gift from the thermal gods. Certain other types of tubing will lie flat on the insulation without lifting at the turns as is the habit of PEX. A grid might still be useful but not so necessary. It can easily be 10 days but more likely 20 days before a poured adobe floor is dry enough to finish with linseed or other surface treatment.

If you go the rammed earth route, I have no experience to pass on. The big question is how to ram the earth without squishing the insulation or flattening the tubing in places. David Easton has a couple of books on rammed earth, I don't know if he has ever rammed a radiant. Quentin Branch is the world's most prolific rammer and I am almost sure from conversations with him that he has never rammed a radiant. If you leave out the insulation, at least 50% of the heat delivered to the floor will move down into the earth and contribute to the neighborhood but not to your own home. And that is in a dry climate soil.

Best book on general adobe construction is P.G. McHenry's "Adobe Build It Yourself". If there is a book on floors it is probably in the Straw Bale camp. They do lots of mud plaster and mud floors. The best floor adobe is like the best mix for bricks, plaster and mortar. 70% sand and 30% clay.

How thick is the adobe after the pour? Do you end up pouring 1 thick layer or multiple layers?

I always pour 3-1/2 inch floor slabs just like concrete. We set up screeds and strike it off in the same manner as concrete. It's a long wait for it to dry out but we get several chances to trowel it as it dries in case it is not flat enough or too many cracks develop. People who are still somehow my friends think I am nuts and pour in 1-inch
layers. It dries quicker but it takes three or four cycles so the wait time in the end is the same. I think they are nuts.

At 300 psi a dropped plate will still break and not bounce back up into your hands. It probably takes very sensitive feet to tell the difference between adobe and rammed earth and concrete. I am sure there are folks at the Oroville complex in India who have the ability.

I wonder if you could get some hog panels and just tie them on the parts of the PEX tubing where the tubing bends. That way, you're not "wasting" the hog fence where the PEX lays in a straight line.

That should work. In fact further savings might be realized by going back to remesh and cutting it into 3x3 or 4x4 squares. For a small area it can be more easily bent into a semblance of a flat plane.

Q: I live in the south of Italy and would like to build my deck from stabilized rammed earth; is it possible? I can find no information on exterior earth floors. I have a 8-10 inch thick pad of rubble and would like to cover it in a stabilized rammed earth floor. It has no roof but is slightly sheltered. I do not mind annual maintenance (it is about 15ft by 15ft).

A: Stabilized Rammed Earth will work great. Just make sure that the surface has a slight slope and that there are no places where water will accumulate after a rain. Most of what we know about rammed earth floors we learned from Romans and Italians.

Q: We are doing poured earth floors with hydronics in Tasmania, Australia, and were going to do two 2" layers, with the hydronics in the top layer. However, I was wondering if 2" allows enough room for the hydronics, without "ghosting", and whether a 1.5" layer followed by a 2.5" layer with the hydronics in it might be more suitable?

A: I think the 1.5" layer followed by the 2.5" layer with the hydronics will work fine. I interpret ghosting as what we call telegraphing, that is, that the outline of the hydronics can be seen on the surface of the floor. I think your 2.5" layer will work fine to contain the hydronics and minimize ghosting.The floor will work best if you have insulation under the adobe to encourage the heat to move up rather than down. Just in case you are not contemplating insulation below, our experience in New Mexico is that it cuts fuel costs in half.

Q: My friend is pouring an adobe floor; he has 5" sections poured over the entire floor and needs to add 3" more in one continuous pour (1500sf). But he is wondering what will happen to the mud/straw mix if it freezes and thaws some before it hardens. We think it may turn to dust but aren't sure. The floor is under cover.

A: It is always best to protect any project with wet mud from freezing. If it freezes, it expands. A floor that freezes will most likely just go back to being a floor once it thaws due to gravity pulling it back into place. If it is quite wet and you are not sure of the outcome, it can be troweled to make sure that it is re-consolidated. If it is drier and it
freezes, the expansion might indeed break some of the bonds established by the clay as it dries. Clay is not bonded by chemical reaction as is cement in concrete. Chemical actions will not renew themselves but the clay drying can renew itself. Again, some more troweling and even adding more water will make it all as it had been originally. That is the worst case scenario: getting it wet again, re-troweling and then putting straw on top of the cover you are using. Adobe always gives you a second chance. And a third.

Q: I would like to build an adobe floor in a small casita. I plan on using adobe block as the sub-floor with a finish layer of adobe over that. How thick should I make the finish layer, and what percentage clay/sand mixture should I use in the finish? I plan to finish the top layer with linseed oil (several coats).

A: A one-inch pour over the adobe bricks should work well. 30% clay and 70%coarse sand works nicely. Once it is quite dry, linseed oil should go on full strength for the first coat to load up the pores more quickly. Wipe up any oil that is on the surface after 20 minutes. Once the floor seems saturated, the oil can be thinned with turpentine, paint thinner or citrus oil and perhaps a touch of Japan drier from an art supply store. The thinning helps promote oxidation of the final coat so you don't have to wait forever to use the floor. Always mop up any oil that stays on the surface of any coat or it will become gummy. Put rags in a closed tin can or in a bucket of water. Linseed oil is what is used in Army and fire department videos to demonstrate spontaneous combustion. We know my wife loves me because she got the hose and put out the fire in the back of the Ford pickup that she hated before it was totally burned up.

Q: My thesis design project focuses on regenerative designs and I intend to specify fibre reinforced adobe for the wall system. Which floor system is preferred to use for an adobe construction reaching 2-3 stories.

A: For three story construction, the first story wall will need to be a minimum 45 cm in width, the second 35 cm and the third 25cm and the wall thicknesses must step back in this manner. If a three story wall was to be one width from bottom to top it would need to be 75 cm. This is because there is a height to width ratio of ten for adobe walls. Assuming each floor to be 2.5 meters, the full height would be 7.5 meters and one tenth of that gives the 75 cm. This rule is enforced by gravity. The fiber reinforcement will have little or no influence on the compressive strength of the adobe but if properly done it could greatly increase the tensile strength. Wall height to thickness ratios, however, rely primarily on compressive strength.

Should you choose the step back system of walls, at the second and third stories you will have a nice ledge of 10 cm which is perfect to attach a plate or ledger to attach floor joists to support a wood floor. Your first floor could be a poured adobe floor, a pounded adobe floor, a brick on sand floor, a concrete floor or just to keep it like the floors above, a suspended wood floor as long as there is a crawl space underneath.

Q: We are building a cabin and would like to have solar radiant heat under a dirt or adobe block floor. Is this a good idea?

A: A radiant adobe floor will work fine. Insulate underneath. I always used 2" blue polystyrene from Dow. For those who object to long chain hydrocarbons within the house envelope, there are alternative such as 5" depth of 3/8" pumice with a very competent moisture barrier underneath it. I think it is now a code requirement but I always obeyed the law with the highest enforcement - The Third Law of Thermodynamics.

Q: We are just about to purchase a mud brick house in Bulgaria. As there are tenants in the house right now I could not get a good look at the floors but under the carpeting I could see they are very bumpy and lumpy. My plan would be to lift all carpeting then fill in any holes/broken bits of the floor. I would like to then over cover the floors with either T&G strip wood, fitted carpets, laminate flooring or ceramic tiles.(still need to decide which covering to go with) The bathroom, however, for sure would be ceramic floor tiles. So my problem is once I have filled/repaired any holes or damage to the mud floor can I or should I lay a screed (6:1 sand cement mix) on top of the mud to get it level and strong.

A: With earthen floors, I would go with carpet to preserve the breathability of the earth. Anything with assembled parts such as T&G strip wood or ceramic tiles may not hold together well on earth and would restrict movement of moisture vapor. If it were my own home I would level the floors as well as possible and put on several coats of linseed oil and let them shine. Linseed oil is vapor permeable to a degree that works well with earth floors. That's what I have in our living room, two bedrooms and the utility room. I don't have advice for the bathroom floor yet.

Q:  I need to build my aunt a floor for about 300 quid. It was a raised suspended timber but dry rotted, so I ripped them out. Now the subfloor is of rammed earth and cinders, real coal cinders. Beside this floor is earth and quarry tile floor. Everyone tells me to use cement or timber but I am not good with wood I have made cob before but nowhere can I buy or source clay in this country all our clay pits closed after ww2. My wonder is to use the least amount of sand gravel and fill 8 inches of floor. I think 2 sand insulation to fill then sand earth and lime to make more hard, then adobe of terracotta to match quarry tiles in the next room. But I don't want to work with cement if I mess up there is no solution. Insulation can fill much of the space so less back breaking work, and sand not too difficult, but if I am to use 3 inch adobe that is too expensive to buy clay. So I want to use only one inch adobe with soil like sand beneath. Can I make a big mistake?

A: Yes, Eli, it's a really bad idea to think that you cannot make an adobe floor if you have been able to make cob. Adobe is the same soil as cob but without so much straw. If you fill the space between the earth and cinders, use several inches of a larger gravel without sand. 2cm to 3cm will work - around an inch. Gravel will not support capillary action and will stop the upward movement of moisture. Insulation under the floor might be useful but the only insulations we use in USA are polystyrene and it is not cheap. You could omit insulation unless you are in a very cold climate such as Norway or Taos, New Mexico, USA. A 1-inch, 2- to 3-cm adobe floor will break up after a short time of foot traffic. 3-inches, 8-cm, will be more satisfactory. You can finish that floor with linseed oil - never allow puddles to remain on the surface or it becomes forever gummy - or you can cover it with quarry tiles or fired terracotta tiles. 100 years is proof enough.

Q: I am just beginning the renovation of a Cognac Domaine in SW France. In my first building there is a compacted earth floor. I was going to dig it up and lay a concrete slab. I wanted to know if I could lay some stone slabs/tiles on top of the earth instead. I am unsure of its composition but it is super old and solid. Of course there is no damp proof membrane underneath.

A: Sounds as if you have a wonderful project ahead of you. Around here earthen floors are highly prized and at the same time often neglected. Compacted, or poured like concrete, or bricks laid flat in mud grout all lead to a great floor. On existing floors several coats of boiled linseed oil can work wonders. Start with full strength oil, then half and half with turpentine, paint thinner, or citrus oil thinner. After each application, any oil that remains on the surface after twenty minutes needs to be spread to dry areas or blotted up so that there is no film on the surface. As artists who work with oil knows, that film or worse, puddles, will turn to gum. The 50/50 mix aids in curing and I have been known to add a little Japan drier, another artists trick.

The linseed oil treatment will give a leather-like surface that is surprisingly resilient and tough. It will also be liquid water impermeable and water vapor permeable so that dampness moving up from the ground is not totally trapped below the surface. A dropped bottle will most likely not bounce right back into your hands but it is a persistent myth that we would like to believe. From the matte finish like leather, one can move up to a polished surface or in between, a shiny surface with additional coats of oil. Linseed is the oil they tell us about at fire department meetings and rags soaked in linseed will self ignite. The curing of linseed oil is slow oxidation chemistry. So blotting rags need to be in a closed tin, or in a bucket with water or left individually on the ground to oxidize their hearts out.

Earthen floors will certainly support stones larger than 30-cm in length and width and two- to three-centimeters minimum in thickness depending on the hardness of the stone.  One does not have to do the entire floor. I embed stones in high traffic areas and in changes in level or steps. The Millicent Rogers Museum in Taos, NM, USA has wonderful adobe floors and steps. The same goes for tile. Larger tile that is stronger can easily go down over an earthen floor. It takes a little practice and there is a learning curve as with any tile job. I bed tiles down in mud mortar but it takes a long time to dry enough for the floor to be usable. Probably cement or cement/lime mortars/adhesives would work but I don't have experience with them. Again, larger, stronger tiles of 30 x 30-cm will be better to spread the load of whatever heavy traffic they may bear. Should you want to support a Bosendorfer piano for a vigorous performance, three large stones in the right places will assure a successful evening.

In short, you can do most anything with an earthen floor that you can do with concrete but concrete will tolerate a higher level of moisture. Both earth and concrete will transmit water vapor upwards and out if there is a constant source below. Sometimes a moisture barrier can have a negative effect when rising damp has nowhere to go and has to seek other routes such as walls or else it becomes plastic down below. If I had a floor that was super old and solid, I would do the least possible to disturb its originality. My chair is grinding slightly on just such a floor right now. In a year or two I will get motivated to do some patching and oiling.

Q: We just purchased an 1,100 sf adobe home in El Paso, TX. It is 118 years old and appears to be very sound. It has wooden floors and previous owners installed laminated flooring on top of original floor. In the four months there I've noticed a smell that builds up in the master bedroom and I'd like to find the source and eliminate it. I think it may be the flooring and am considering filling in the (1'-2') crawl space with sand and placing recycled bricks to achieve a carriage house look. Because of its age I'm thinking it may have a stone footing or maybe cement. The house is a mission style home, a box divided into four equal rooms. All walls are adobe so each has a footing supporting that wall. Here's the question. Do you foresee any problems with my plan to remove wooden subfloor and filling with sand and brick? Would I need a vapor barrier under the sand? I need help in whatever I may not yet be considering.

A: The big task is to locate the exact source of the smell. The crawl space between the soil and the floor is often a breeding ground for mold and spores. However in El Paso where the air is dry and the water table is deep unless you are close to the Rio Bravo there should be less of an opportunity for mold and spores to flourish. If the crawl space is sealed and has no ventilation opportunity and that coupled with runoff from the occasional rain that might get channeled into the ground around the house then there could be a chance for such growth in El Paso.

You probably do have a concrete foundation since cement was available in the area around 1900. A stone foundation would be just as serviceable. There is always some moisture vapor working up from the ground, into a crawl space and on up into the living space of a house. The original floor was most likely not moisture vapor tight. Laminated flooring usually goes down on a thin foam pad that is more moisture vapor impermeable and the interlocking, pre-finished flooring itself usually constitutes a fairly tight, low impermeable surface. So, indeed, it could be the addition of the laminated floor that stopped the upward migration of water and trapping it in the crawl space.

If you replace the present system with sand and brick, start with six inches of 3/4-inch gravel. Follow that with enough sand or base course to get up to the level of the bottom of the bricks. Clean gravel does not have small interstitial spaces and will not support capillarity. That will stop the upward migration of liquid moisture. Moisture vapor will still be inclined to move up since any house placed on a site acts like a vacuum bell as the warmer air in the house rises and creates a bit of a vacuum on the soil below. In radon mitigation procedures for new or existing buildings the simplest solution is to have perforated 4-inch pipe placed in the gravel below a floor and to join the horizontal perf pipe to vertical stacks that go up through the roof. That mainly breaks the vacuum on the ground so the house does not suck radon upwards. It would also break the vacuum that tends to pull moisture vapor upwards.

As for the question of a vapor barrier under the new floor, I don't have a good answer. Wherever you place the vapor barrier there will be moisture build-up below it. With the right conditions there goes the mold and spores again, just lower down. My own inclination and my own procedure with brick on sand floors was to not put down a vapor barrier.   I just liked the thought that if moisture were present, it had a route to get up and out

Do you think that removing the existing flooring and joists would weaken the wall structures or can these monolithic walls support the roof on their own?  I think they already are because the floor joists might have been added after the walls went up.

I am almost certain that the floor system will have no effect on the walls and their ability to support the roof. If the joists are inserted into the adobe walls it would be good to break them up and remove them and then pack the holes with adobe mud.

Q: 3 years ago we purchased our lovely adobe home in Corrales, NM. Due to a roof leak (now repaired), we pulled the carpet in the master bedroom and were delightfully surprised to find an adobe floor. We would love to restore it. What is the best way to remove the carpet glue and will just resealing it with linseed oil get back the shine or do we need to sand and reseal? We have radiant heat underneath.

A: Most carpet glues are not water based so it may take some chemical to soften it. Then it's elbow grease and a sharp floor scraper - like a straightened out hoe. A carpet/flooring business might be better able to advise you. Then linseed oil will do the trick Thin it half and half with thinner or turpentine or citrus oil thinner. After twenty minutes wipe or blot up any oil that remains on the surface. That which remains will turn gummy and ruin your day. Or week. Several applications may be needed to get the shine you want. Blot after each. Put oily rags or paper towels in a can of water. Linseed oil is the stuff that spontaneously combusts as every volunteer fireman gets to see in training videos. You have a treasure!

A: (Kelly) Probably the best way to remove the glue is with some sort of scraper that physically releases it from the adobe below. If you are lucky this will leave the surface unscarred and you can just shine it up with some more linseed oil (assuming that this was the original finish). If it was waxed then another application of wax may do the trick. Chances are that this will result in some unevenness in the surface which will need to be repaired. I suppose that it would be possible to use a floor sander to grind it all down to an even surface, and then refinish it. Or it might be possible to find a similar adobe mix and fill in the depressions with moistened adobe paste, then refinish it once the adobe is dry. This is all likely to require some experimentation.

Q: I have two topics: (1) I'm looking to purchase a small 1931 sdobe in southern San Luis Valley in Colorado. The electrical wiring is old and insufficient, and not up to code. That must be corrected. The floor is framed with subfloor and vinyl. I am considering removing the flooring to expose the crawl space to make the electrical renovation easier, maybe cheaper. I'm also considering replacing the existing floor system with an earthen floor, and pex radiant heat. What design would you recommend to bring an radiant adobe floor up to the current finished floor level?

(2) We would live in that home while we build a slightly larger, double walled, super insulated home. I am considering slab on grade with radiant floor heat, but would prefer not to use so much concrete. I love the idea of earthen floors. Is there a particular design for high traffic areas, and wet areas like the bathroom or kitchen? Also, I am a little confused by the term "clay". When you use the ratio 30 clay/70 sand, what is the quality of the clay that must be used.

A: Southern SLV has a high water table in many areas. If you do not find mold and spores under the present floor you are probably in an area of low water table. When we say clay we refer to the sticky particles in earth that are small enough to pass through a #200 standard soil analysis sieve. If you want to go from a crawl space to a radiant heated adobe floor all you need is heavy labor. Allow four inches for the adobe floor. It can be poured in one pour which has always been my technique, or it can be done in three or four pours to get the same thickness as is done by many people. Either way, it takes three weeks to dry fully in SLV summer weather. Finish it off with several coats of linseed oil and always wipe or blot any oil on the surface after 20 minutes. Under the adobe, two-inches of sand with 10-10/6-6 remesh or hog panels to which you can attach the radiant tubing. Under that two-inches of blue or grey code rigid foam polystyrene insulation. Under that, four inches of uniformly sized gravel between 3/8" and 1" which will not support capillary action. From there on down to the existing bottom of the crawl space can be more gravel or compacted base course. The existing bottom should be compacted, also.

You can run wiring under the floor. NEC, the National Electrical Code requires that NMC cable be used in adobe walls. That's also known as Barn Cable and is not readily available in the SLV. Next step up the chart is UF, underground feeder and that is readily available but costs considerably more than NMA, known as Romex. Since you are thinking of running under the floor, UF will meet your needs. An electrician might suggest that you use one of the plastic conduits under the floor.

I presume you are thinking a double withe wall with space in between for insulation. With lots of windows on the south, few on the north and not too many on the east and west you will have a tried and true SLV passive solar adobe home.

Q: I live in Ecuador and am in the process of building an adobe house. The builders put the second floor on but it is only hardwood flooring. Should there be some kind of ceiling under the flooring? From the first floor you look up and see the flooring above.

A: In New Mexico and Arizona, looking up to see the beams and bottom of the floor above is beyond acceptable and is pridefully carried into conversations at cocktail parties as the highest form of one-upmanship. The only thing worse is wax polishing adobe plastered walls. If the hardwood floor is strong enough to support walking around without deflecting, then there is no structural problem.  And, if looking at your beams and the bottom of the floor is acceptable to you, then you are done.

We think it’s very noisy with just the tongue and groove hardwood floor above. As when someone drops something on the floor. Has this been an issue for you in the past? Do you have rugs on the second floor to absorb some of the sound?

Rugs or a carpet would be a good start to muffle impact sounds and would be the most cost effective. Speech and music may still be transmitted. The only way to achieve total or nearly total sound isolation would be with two separate support systems that are independent of each other: one with your existing structural members and a second above or below the present system. That's how it's often done in quality apartment buildings.

Q: I am building an earthbag house and we are at the spot to do the floor. Can I just make a tamped earth floor, with my clay rich earth and finish it with linseed oil? Is there any danger that some moisturer could affect the walls and be bad in any way with this setting? I'm very keen to be able to make a floor with just dirt if possible, but of course I'm open for suggestions. I live in a tropical humid climate and the house will have plenty on ventilation and its on a hill.

A: In the beginning, most dirt floors were tamped with local dirt, often just the dirt that was within the walls. Just people walking around in the rooms did the job. The nice thing about tamping with high clay is that it will not crack as it would if it were poured and you don't have a long wait for the floor to dry out. The trick will be adding dirt here and there to get the floor level and smooth as suits your taste. A little moisture will help in the tamping but don't go more than a cup, just maybe a pint per wheelbarrow. Your humid climate might provide you with dirt that has just the right moisture content. When the floor rings under the tamper, that tells you that you're done and the floor is nice and hard. If it does not ring, you still might be done. Give it a few days to dry what moisture is there before applying the linseed. As you may know, several layers of linseed may be needed but most important of all is to blot up any linseed remaining on the surface after twenty minutes soaking in. Linseed oil remaining on the surface becomes perpetual gum. Linseed oil soaked rags or paper towels are the champion spontaneous combustion producers.

Q: Is it possible to build a large earthen floor on top of a scoria base for good insulation? If so, how thick would each layer be?

A: (Kelly) I did just what you propose in the earthbag home I built in Colorado, using about 6" of scoria under 3" to 4" of adobe, and it worked just fine.

Q: I've built a house and we planned to put in an earthen floor, however we have discovered that there may be a 'seep' below the house. There are three small areas where water has seeped up. All the proper layers have been laid: sand, gravel, insulation, plastic, road base - we only have to pour the final 3/4 " Earthen layer. With this water problem, however, we are debating whether we should proceed with the Earthen floor or have a concrete floor poured instead. So, my question is is an Earthen floor nearly as hard as a concrete floor and therefore potentially as effective in keeping dampness from coming through? What if we added some portland cement to our Earthen floor mix?

A: All the earthen floors I have done were single pours around 3.5 inches in depth. Occasionally we put down gravel as a capillary break. We never had the situation such as you describe. An earthen floor is not at all as hard as a concrete floor with a compressive strength of around 300 psi compared to 3000 psi. Hardness has little to do with moisture transmission. The molecular composition governs moisture permeability. Most concrete formulations allow liquid moisture to move through readily. Ideas:

1. Just go ahead with the adobe layer and do not make much effort to make it moisture liquid or vapor impermeable. The damp will rise and evaporate as long as there are no floor coverings. 

2. It's Michigan, however. There may be too much moisture coming up and the adobe will turn back to mud so a concrete layer might be better. Moisture will still come up through the concrete. Concrete is perfectly happy in a damp or even submerged environment. 

3.Lift (dig) up the existing layers to make a trench for perforated pipe as low as possible to form an interior French drain that moves water by gravity or pump to an exterior discharge pump.

4.Probably no to the the idea of adding  cement to the adobe mud. That's soil cement and won't be any more effective than adobe.

5. Proceed with a cement layer and use the most permeable materials for rugs or any other floor coverings.

Q: We are putting an adobe floor into our tiny house in North Carolina. We are in the Appalachian foothills, and our soil is just about 100% clay (we tested it). I’ve read about how to do this and watched a number of videos as well. Two questions have not gotten answered though. Maybe you can help with these?

1. How do we determine the correct ratio of sand to clay to straw? I’ve read anywhere from 70:30 to 50:50 sand and clay and nothing about how much straw…

2. There are currently about 2ft of gravel where the floor is going. My plan was to compact that as much as possible with a plate vibrator, put a vapor barrier down, sand on top to level it perfectly, then rigid foam board insulation, then floor heat pipes that get encased in the adobe. How does that sound?Would you do anything differently?

A: 1. I always try to get the 30% clay/ 70% sand mix.  If you did a jar test for your soil, it might not actually be 100% clay. It would not be a bad idea to do a test mix and see how it works out for a 12" x 12" square in a wood form that is the same thickness as the floor you plan to pour. If your mix is too high in clay, it will crack. My first floors did that and I filled the cracks with a mud slip and it looks like flagstone. I rarely put straw in adobe bricks, mortar or floors. But it can't hurt and if the mud is crack-prone, high-clay content, the straw can decrease or eliminate cracking. Maybe. Straw should be chopped, shredded or flailed to 1-inch lengths. If it's available, barley straw in 2-inch lengths works even better. Try three- to five-handfuls per wheelbarrow of mud.

2.  Your plan sounds good. Use blue polystyrene insulation board with a 12- or 15-pound crush resistance rating. Most common is the Dow blueboard. With radiant heating tubes in the floor you should pour a 3-1/2 to 4-inch thick floor. PEX tubing is notorious for not wanting to lie flat. A common solution is to put down metal hog fencing panels which lie flat - and are shipped flat. The PEX can be tied down to the panel with zip ties.

Q: I am trying to find someone who can put an adobe or earth floor in my condo in the San Francisco Bay Area (Palo Alto). I don't have the DIY skills but would love to have that floor as I grew up seeing those in the modest homes of folks in India of my childhood. 

A: A standard adobe floor is 3 to 4 inches thick. That's a lot of weight for your condo to handle. Some people can put down inch thick adobe. Not me.

C: I ended up settling for polished concrete floors instead. Its hard to find the skilled folks to build with natural materials. The pressure from friends and contractors to go with the manufactured vinyl 'luxury' tiles was horrible. The convenience, speed and cost, all favor these terrible options while the talented caring slow and steady pursuit is starved for resources and given no promotion in these times. Rant over.

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