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Straw Bale House: DIY Flooring with Adobe and Flagstone

Dave L HeadshotThe floors of our buildings here at our desert homestead are all different. Adobe and flagstone are the primary materials. One building has flagstone flooring and the other three have adobe floors. Each of the adobe applications used a different set of materials besides adobe and each has turned out to have very different color and texture from the others. We decided against concrete because we were a crew of two and a bit weak in concrete finishing skills. We had helped lay a large concrete patio base for our son and the drying time snuck up on us. The result was not what we would have liked. We knew from previous experience that adobe dries much more slowly and is more forgiving. There is also the comparative benefit of natural material, adobe, versus material with a great amount of embodied energy such as concrete for those considerate of Mother Earth. We do use cement, but try to use it sparingly.

     AB base
In all the floors, we began with a well-tamped sub-floor of AB sand mix such as is used in a road base. With repeated leveling, wetting, and tamping, this material provided us with a solid base for our earth and rock floors. The material was inexpensive and available from our local sand and gravel people.

          Ttamping Floor
For those who don’t have a young fellow teacher ready to help out for a few hours, small power tampers are readily available from tool rental outlets. On damp evenings, my shoulders can still feel the effects of tamping down sub-floors by hand in three buildings plus the shop. We don’t have a rental outlet anywhere within 75 miles of the homestead, so it was a hand-tamper for us.

The results using hand tamping were fine, though the process took longer.  The tamped sub-floor was brought up to two inches below the ultimate finished floor level. The rest of the way would be either stone or layers of adobe.

        First Coat of Floor Plaster
The need to have precisely level floors was not as great in the Bear Cave and the shop, so we simply used wood guides for the layers above the sub-floor.

Using dimension lumber in the same manner as screed boards in concrete work, we spread and smoothed the first layer with a garden hoe and a long, handmade combination trowel and screed called a darby float.

     Leveling Floor
In the main straw bale house, we wanted more precision and were dealing with a larger floor. Armed with an antique surveying level and rod, we put pegs in the subfloor in a grid so that each peg was reachable from two other pegs with a four-foot level. I know that there are wonderful laser levels and such that could do this job as accurately in less time, but we were watching the budget pretty carefully and the tool we used belonged to Barbara’s dad. Hard to beat a tool that works well and costs nothing.

     Plastering Floor
For the main floor, the knee work started when the pegs were in. The floor was built up in three layers including the brushed on aliz. We put in a thick layer, about 1.5 inches, of a damp mixture of  adobe with straw and coarse sand. This was tamped down in much the same manner as the AB. After a few days to nearly dry, a wetter layer of the same material was troweled to the tops of the guide sticks to maintain level.

The final coat was put on in one day to prevent seams and cracking. We screened the adobe to a 1/8 minus clay and used very finely chopped straw. Before this coat was dry, we mixed up some 1/16 minus aliz clay and mixed in to the consistency of heavy paint. This was applied with a wallpaper paste brush and smoothed with a pool trowel. The results were very satisfactory. When the floor dried, we began putting coats of boiled linseed oil on as a sealer. More about that in another blog. The floor in our house is without cracks, level, and a pleasant brown. We will be adding another coat (the fourth) of linseed oil in a few weeks and then will use an acrylic floor wax to bring up a bit of a shine.

     Shop Floor
In the woodshop, I wanted to try an experiment. I read that well-composted horse manure is used around the world as a binder in earth floors. As it happens, we have a neighbor with three delightful manure factories named Bueno, Cody, and Bugsy. When we mixed the adobe in the same manner as for the house, we added one shovel of old manure for each five shovels of other material. The mixture troweled like a dream, has no cracks, and no odor. I would use it again in a heartbeat. While not for fecophobes, this is a great method for those that want a natural binder in adobe.

       Flagstone Floor
In the utility building, we decided to use flagstone. We had found a great buy on a substantial amount of flagstone and knew it would hold up with laundry, shower, and food prep spillages. I actually think a well-oiled adobe floor would do so as well, but we preferred to err on the side of strength and impermeability. There really isn’t much to say about installing flagstone. A simple, but labor intensive, job that requires a good bedding material such as a fine grit sand to accommodate the irregularities in the stone and then finishing the job a good grout and sealer. For grout, we simply used Portland cement in a ratio of 1 part cement, 2 parts sand, and 3 parts small aggregate. We used the 3/8 material left over from screening the adobe as aggregate.

Our floors are all unique in appearance. As is the case with most DIY projects with local natural materials, costs are very low and the rewards are many. While not recommended for those that like a slick, uniform appearance, the variegations in texture and color make these literally one-of-a-kind floors.

If you’re building with straw, cob, earth bags, or other earth-friendly material, you might do well to include an adobe floor.  For more on our desert homesteading experience, you're invited to visit us at Happy building!