Building the Cob Honey House: Part 4 – The Earthen Floor

The Honey House now had a roof and roof top access. The next step was to install a floor. Up until this point the floor had simply been the earth on which the Honey House was built. It looked fine but we wanted something more stable, water tolerant, and wipeable (honey will spill on it, after all) for easy cleaning. This created the perfect excuse to try our hand at making an earthen floor. This is our first earthen floor, but certainly won’t be the last. It was fun to build and has so far been holding up well. See below for how we did it.

We first needed a stable foundation on which to pour the earthen floor. We layed down a layer of rocks pulled out from cob fill base and made up the difference with 3/4″ clear crush gravel. The Honey House is built on a slightly sloped piece of land therefor the gravel had to be poured thicker on one end to level the floor out. Once the gravel was in place the entire floor was perfectly level. At its shallowest it is about 2″ deep. Ideally I think it would be better if it were a little deeper than this, maybe 3-4″. This provides a layer of drainage and acts as a water break between the earth and the floor.

The masses are divided on whether a vapour barrier should be added to an earthen floor. We had some poly left over from doing the garden wall roof so we installed a plastic layer. I don’t think it makes much difference in a structure this size and shape but they say that in a house or larger structure that a floor vapour barrier can prevent water from condensing on the bottom of furniture. On top of the vapour barrier went a layer of road base. This is about 1.5″ thick and was watered in and well tamped down to make a firm level surface on which to pour the floor.

The floor itself is made from the very same clay earth as the walls. First we sifted this through a 1/8″ wire mesh to get all the lumpy bumpies out.

In to this went some spent pottery clay (free from our local pottery studio),

some horse manure mash (made by soaking horse manure in water and then macerating it with a circular saw blade that we welded to a metal bar and chucked in to the hammer drill),

some sharp sand (also sifted through fine mesh),

and some straw (run through the wood chipper and then sifted to make nice short even pieces).

The ratios we used were as follows:

1 part clay earth
1 part pottery clay
3 parts sand
1 part manure
0.5 part straw

We actually tried a variety of small sample batches made with different ratios and unanimously decided on the one listed above as it didn’t crack once dry and it didn’t shed grains of sand when brushed over. There was a good amount of fibre without there being so much that it was difficult to work. I’d recommend you do your own experiments to see how your ingredients work together. We knew our floor would be 3/4″ thick, so that is the thickness we poured the sample floors.

Then it was time to pour. Since our floor is small, we used a screed rail system to ensure an even pour. There are several other ways of levelling a floor depending on its size and shape.

When pouring it we applied firm pressure to really try to work out air bubbles and push the floor in to the rock base below. We worked it over pretty lightly, just enough to level it off. The rough, uneven bits get worked out later, when burnishing.

Once it had set up for a week or so we used rigid foam boards to lightly walk on the floor so as to be able to cut the extra vapour barrier down flush. The floor shrank a little as it dried and pulled away from the edges of the honey house a bit. When we cut down the vapour  barrier we also filled this gap with left over floor mix and pressed it in well. We had to do this again later once it had dried more.

Then we let it sit. We poured this floor in the late autumn so it took a really long time to dry. We were lucky because we had no issues with mushrooms or other plants sprouting which we read was a risk when letting a floor dry slowly. It got to a point where it was very firm but not rock hard. It could tolerate firm pressure from a trowel and not compress when standing on it using a rigid foam pad. Time to burnish.

Burnishing is what makes a boring floor of earth in to a beautiful earthen floor. It is done when the floor is almost dry, like very stiff plasticine. We used a rigid, straight steel trowel which, with ridiculous amounts of force, we dragged across the floor with the near edge just barely lifted off the floor. We reach out, placed the trowel and then pulled it toward us, over and over again. I think I got an epicondylitis from doing this. It was worth it though because it flattens out the high points and fills in the low points. It also just smooths and polishes the entire floor. When we were done the floor was smooth and shiny.

Then we let it dry some more. Once it was fully dry it lightened up substantially which was sad, to me anyway. It was now time to seal it. We used commercially boiled linseed oil which we applied with a sprayer. We did a lot of research before choosing boiled linseed oil as our hardening oil. It has the advantage of hardening quickly and being cheap and easy to find at local hardware stores. It has the disadvantage, however, of containing drying agents, some of which are heavy metals. We took the risk and went for it. You will need to decide for yourself whether you choose a slow drying hardening oil (tung, teak, raw linseed….) or opt for a quicker route.

The floor sucked up the first two coats quickly and we applied repeated coats after that until it started to pool without soaking in. In total we did 5 coats, applied one right after the other. Then we let it dry for a few more weeks. Once the hardening oil was dry we gave it a final finishing with an orbital sander mounted with a high grit (120) sand paper. This just smoothed it out a little more. Time to wax.

We researched earthen floor wax a lot and decided to make our own using our own beeswax from our apiary. It was tricky finding a recipe for this. We melted the wax in to boiled linseed oil in equal parts by weight to volume (ie 100g beeswax to 100 mls of linseed oil). We did this outside on a propane stove because there is a risk of fire when heating linseed oil. Luckily it worked out just fine. We then let the liquid wax/oil blend cool to the consistency of room temperature butter before applying it with a spatula and buffing it in with a rag. It was easy work, compared to burnishing at least, and left a beautiful, shiny, water repellant surface that is easy to wipe down and keep clean.

We’re happy with this floor, especially since it will spend most of its life buried under bee boxes, never to be seen. I would have included a photo of it all finished but it got covered in bee boxes before I could get a chance. I’ll post a photo of it in the spring when the house is emptied out again.

Now that we have the hang of it, I would do a couple of things differently. First of all, I would ensure that there was a thick layer of rock under all parts of the floor. The end of the honey house with the shallower layer of rock cracked in one place. I would also spend a lot more time burnishing and probably make myself some sort of elbow brace to do this. I think we could have gotten this floor even more silky and velvety than it already is. Thirdly, I would have added some tint to darken it. I felt pretty sad when I saw how light it became once it was all dry. I personally preferred the impact of the dark floor. Another option would be to use a colour in which case I would use white pottery clay without supplementing with clay earth, which in these parts is sort of brown-grey when dry. Lastly, I’m not sure I would add straw to my next floor. I personally don’t really like the effect it creates and I think that the fibre in the horse manure does the same job without leaving so much visible fibre.

Overall though, we’re impressed with this floor. It has a hardness similar to concrete but feels soft and gentle underfoot. It is easy to keep clean and looks nice. I would happily live with an earthen floor in my home though I would add a layer of insulation below it if I were building one in my house. Hopefully one day I will be lucky enough to make that a reality.

The last job was to finish the doors and plaster the beast. Details coming soon.