Earthen floors

September 11, 2015

In the architectural drawings for my house, the floor finish was described as “Earthen Floor on slab”. The plan reviewer at the county offices was unsure about what this meant and he finally tilted his head a little and asked me: “Is this like a dirt floor?” When I explained to him what it was he just sort of nodded and approved, as long as “It wasn’t dusty”.

 

Whatever floor finish you choose, there will be advantages and disadvantaged to every choice. In the case of earthen floors however, the advantages seem to far outweigh the disadvantages. The relative softness (compared to hardwood floors, concrete slabs or tiles) and the subtle imperfections make an earthen floor feel gentler to your bones and natural to your feet, as if you were walking in the out-of-doors. Earthen floors are also great sound absorbers, making your house more quiet. They are easy to clean, long lasting, simple to build and easy to repair. They can be colored, they look beautiful and absorb warmth from the sun. They are perfect for radiant floor heating.

 

What is an earthen floor? It is essentially a mixture of sand, very finely chopped straw and clay, mixed together into a “cake batter” consistency and then spread with a trowel on to a hard, stable sub-surface. Once dry, it is then usually saturated with several treatments of linseed oil (thinned with turpentine after the first layer).

 

In existing homes, the sub-surface can be a concrete slab, sturdy plywood, chip board (OSB) or concrete board. For our natural cottages, we usually start with a well compacted and dried “cob-like” material. In my house, I started from grade with 6 inches of round drainage gravel, topped off with ripped up blue tarps (to keep the fines of the next layer from silting up the drainage rock). Then I added 6 inches of “3/4-inch minus” crushed rock with a little clay mixed in. This is sometimes referred to as “road base” (the material they put on gravel roads). It is essentially a very crude cob mix (without the straw). After spreading this “road base” out over the surface, I used a mechanical tamper, called a “Jumping Jack”, to create a rock hard and reasonably level surface, about 3/4 inch below where I wanted my finished-floor to be. I also made sure that I moistened the material a bit, so it compacted tighter and I ended up with a harder surface. You can also tamp it by hand, using a log on which you make some handles.

 

I then framed and finished my house, and put in the final floor layer as the last thing that needed to be done. I made my “cake batter” mixture out of 70% sand, 30% clay and about 10% straw. All these ingredients were sifted through a window screen and mixed with water in a wheelbarrow . A trowel called a “Pool float” was used to trowel it on.

It usually takes about a week for the finished coat to dry, depending on the weather and the air circulation. It is important not to walk on it during the drying process, and make sure to inform your cats about that. Once dry, we applied the linseed oil with a rag about 3-4 times. You don't have to wait for the layers to dry; you can do one after the other.

 

After the linseed oil was dry, it took a few more weeks before the floor was hard enough to take some serious abuse (such as chair legs), but then we did have a very, very durable floor.

 

How about the cost? I calculated that from bare dirt to finished floor, it cost me about $1 per square foot. That included equipment rental, all the materials and the linseed oil.

 

The only disadvantage I have found is that due to the rough texture of the floor, your socks wear out a bit faster. But a nice pair of slippers easily solves this problem! There is no reason why there can’t be an earthen floor in every home.

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