In June, I finished installing the earthen floor in my cob house. In October, I built the base layer of the earthen floor, a 2.5″ thick mix of sand, clay, and straw. It dried over fall and winter (very slooowly), and once I finished plastering my walls, I moved onto completing the floor this spring. Here’s how it happened:
Preparing the finish earth floor
My recipe for the final earthen floor layer included the following:
- 3 buckets 1/8″ sifted sand
- 1 bucket clay
- 1/2 bucket cow manure
- chopped and sifted straw (to taste)
The most tedious part of making the cob floor mix was making the chopped straw. I used a weed whacker in a barrel to chop the straw (in small quantities at a time), and then I sifted the straw through either a 1/4″ or 1/8″ screen.
I decided to add the straw directly into the mix. I’ve read that others have chosen to actually sprinkle it on the floor and trowel it in, but I saw no difference.
The mix I prepared was fairly dry, but not so dry that it was that difficult to mix by foot. I would call it “stiff”. It was wet enough to trowel smooth with effort.
Laying the earthen floor
After wetting the base floor with a watering can, I dumped buckets full of the floor mix on the surface, starting in the “corner” of the house, and then working towards the door. I smacked the mix with my hands to flatten it and make it easier to trowel. I did not use screed boards, so my floor is not perfectly level. It has some light, natural undulations.
After hitting the floor with my hands, I went over it with a trowel. I pressed fairly hard to obtain a smooth surface.
The final floor layer is about 1.5″ thick. If I were to do it again, I would only make the final floor about a 1/2″ thick. The floor took about four weeks (with a fan blowing over the surface much of the daytime) to dry because the weather was so damp! (And I got mushrooms in my earthen floor as a result!)
Besides the mushrooms, there were a few small cracks that developed during drying. None were wider than the width of several sheets of paper, but at least a couple were over a foot long.
In another earthen floor post, I will detail how I dealt with filling in cracks (and removing mushroom scum) and sealing the floor with linseed oil.