How To Pour A Rammed Earth Floor/Adobe Floor

by Tony Sirna

At Dancing Rabbit Ecovillage, we’ve found our earthen floor/adobe floor hybrid to be a cheap, easy to install, durable ecological flooring solution. Built with gravel, sand, clay, straw, and linseed oil, it is made of local natural materials except for a plastic moisture barrier necessary in our area.

Performance of Our Earth/Adobe Floors

Two years ago we poured adobe floors in two of our straw bale homes. Each was installed and finished in a few weeks and has been performing well ever since. The floors are sweepable and moppable and have dealt well with foot traffic. The only damage has come from moving furniture that scraped along the ground. They’ve even survived some leaky doors and major spills with no lasting effects.

In addition, the floors beautifully complement our earth-plastered walls and give the rooms a warm color while regulating the temperature. Even during our hot Missouri summers the homes stay cool inside because of the floors’ thermal mass. Of course in the winter the floor is a little cold on your toes but seems to help moderate the temperature for easy heating.

The step-by-step process and recipe we used in pouring our earthen/adobe floors:

1. Each home had a perimeter foundation which we filled with 1-inch gravel that was “washed” and “cleaned” for drainage. “Washed” and “cleaned” are terms our quarry uses to mean “washed with water to remove dust” and “cleaned of gravel smaller than the given size.” (Don’t use 1-inch surfacing gravel which is used on roadways.) Some books on earth floors say that this should be enough to keep your floor dry. We have very clayey soils with poor drainage and heavy rainfalls so we decided to install a moisture barrier.
2. We bought a sheet of 30-mil plastic from Unit Liner, a pond-supplies retailer (800-633-4603). Sheets are available in various sizes and thicknesses, but the one we got cost $0.30 per square foot. Before laying down the plastic you need to protect it from the sharp gravel below. We used a different method in each room: old carpet we had dumpster-dived; a layer of sand about an inch thick (a common suggestion); and a layer of flattened cardboard. After laying down the plastic you’ll need to put something to protect it on top as well. We used a 1-inch layer of sand.
3. Now comes the rammed earth part. We purchased a product called “road base” or “rolled stone base” from our local quarry.
   
   It’s made up of clay, sand, and various sizes of gravel that allow it to compact tightly and firmly. The highway department uses it under concrete and asphalt on roads and parking lots. We added a few inches at a time and tamped it in place by hand after spraying lightly with water. We ended up with 4-6 inches of compacted road base.
4. The next step is what makes this a hybrid of rammed earth and adobe floors. We took our standard earth plaster recipe mix (6 parts sand, 2 parts clay, 1 part finely chopped straw) and applied a 1-inch thick layer to the floor just as you would a finish coat to your walls. The plaster was troweled smooth and when it was almost dry to the touch (some call this “leather hard”) we burnished it with scrap pieces of our moisture barrier to give it a smooth, almost shiny appearance. We allowed the plaster to completely dry which took less than a week during the summer but much longer during a cold spell in October. We highly recommend doing this in the summer to avoid problems with mold during a long drying time.
5. After the plaster was completely dry we applied four coats of linseed oil. We used BioShield Penetrating Oil Sealer which is available from the BioShield Paint Company (www.bioshieldpaint.com, 800-621-2591). Their product is a little more expensive than other linseed oils at $40 a gallon but it is all natural and has lead-free dryers. We used about 7.5 gallons to do about 480 square feet of floor. The first coat is applied at full strength using a rag to spread the oil on the floor, putting on as much as possible without leaving any pools or puddles. After allowing this to dry completely (a day or two), you’re ready for the second coat. For this coat we mixed three parts oil to one part BioShield Natural Citrus Thinner and applied in the same manner as the first coat. This allows the second coat to penetrate deeply into the floor. For the third coat we mixed two parts oil to two parts thinner, and for the fourth we mixed one part oil to three parts thinner. Remember to allow each coat to dry completely and make sure all the oil soaks in on each coat. The oiling process took us under a week to complete. Now you have an earthen floor and you’re probably itching to move in. We recommend waiting a few more days for the floor to completely dry and the citrus and linseed smell to dissipate.

For one room in our home, approximately 180 square feet, we estimate it took about 60 person-hours to complete the floor not counting the original drainage gravel that was put in during the foundation process. Total costs will vary, depending on gravel, road base and sand costs for your area.