An earthen floor

On Thursday we made a significant step in the process of building our home. Over the course of 8 hours we laid 4 inches of mud into the footprint of our building to serve as our floor. It was our first “material” departure from conventional building into the realm of natural and earthen building (though much of our wood is sustainably-harvested beetle-kill fir, rather than conventionally monocultured wood).

Hooray floor!

Hooray floor!

Prior to our floor, we have built with conventional materials. A concrete foundation. Milled lumber. Rigid foam board insulation. You will find all of these things in most residential construction. You can be sure, however, that you won’t find mud. But it’s not the symbolic departure from the conventional that excites me. It’s the sheer joy of working with the earth and making it a part of our home. On Thursday we measured, mixed, and wheelbarrowed buckets of mud into our home’s interior where we pushed it around, patted it down, and troweled it off into a smooth, fairly level floor. It was dirty, sweaty, and fun. Compared to a concrete floor, which is ready-mixed and poured directly out of a truck, our earthen floor was much more interactive. We felt the floor and we worked with it. We accidentally stepped on our smooth floor and the floor let us know it wasn’t ready for that yet by caving into a footprint. We troweled it up and down as we set the level of our floor with each and every stroke. We will feel these strokes as we walk on the floor the next couple months before we finish the floor with a thin plaster and an oil and beeswax seal.

Puttin' on the floor.

Put it on.

Smoothin' it out.

Smooth it out.

Finish it off.

Finish it off.

So what is our floor made of? We needed only mix three components together to get our floor material: “reject sand” from a local gravel operation, which is the soil washed out of the gravel when it is cleaned; water; and a bit of straw. The soil that we use is the most important part – it must have the right clay content, the right sand content, and a minimum of silt.The clay provides cohesion to the mix, keeping it together because of the small size and unique shape of individual clay particles. The sand provides strength and infill and is the primary constituent of the mix because it will make sure our floor doesn’t expand and contract. And silt is mixed in, but doesn’t serve a structural purpose because it doesn’t bond or give strength. We are lucky to have a very good mix in the “reject” material from the gravel operation and from there we just add water and a bit of straw to get our mix. The straw is not necessary, but serves to bind the mix together in a different way than clay and prevents cracking.

Add sand

Add dirt,

straw,

water,
water,
and mix.

and mix.

We have given our floor the weekend off to prepare for 10 sets of boots stomping around on it for the next 3 months. Towards the end of the build we will return to our surely-to-be well-used floor and give it thin layer of plaster (the same as our floor mix) to smooth and level it out and a seal of oil and beeswax to create a water seal, greater durability, and a finished look and feel.

As our floor rests, so do we. The intern crew had the day off Friday and made full use of it with a bonfire brunch at the intern house and some fun outdoor activities on the first Spring-like day we have had in Moab!

The CR intern family.

The CR intern family.

A footnote: Though I described this as our first “material” departure from conventional building, I only meant it in the strict sense of physical building constituents. Our house departs from conventional building into the world of natural building from before the very first pencil line of our design. The house design is passive solar, which dictates many elements of the building including the earthen floor, which serves as a thermal mass, or heating and cooling unit. Look forward to a future discussion on passive solar!

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