Earthen Floor in Hotchkiss, Colorado

Enough about rocket stoves, what about the earthen floor?

Earlier in the summer, David and Maureen had, with Doni Kiffmeier, installed the rough base layer of the earthen floor.  Having missed that event, I don't have the exact details, but it goes something like this.  The bare earth was leveled and tamped.  A 2" thick layer of rigid insulation (blueboard polystyrene, R10/inch) was put down to keep the heat from the home from being conducted out through the floor.  Roadbase gravel was then brought in (using a bucket loader through a window opening) and spread on the floor several inches deep, then leveled and compacted.  PEX hydronic radiant heat tubing was installed in a serpentine fashion at 12" on center, on top of the road base, which in retrospect was a mistake.  It should have been installed deeper down, in the middle of the roadbase.  The shallow installation of the flexible tubing later caused the base layer of earthen floor material to crack above the tubes.  Then, a dry earthen floor mix was prepared (I believe this was a small amount of clay slip, mixed with a large amount of coursely screened sand/gravel) and a small amount of water as needed to make a tamp-able mix.  The mix was then spread 1-1/2" deep, leveled and tamped with homemade tampers.  Afterwards, heated linseed oil was painted on in several layers.  This proved to be another problem, as the dry-tamp floor quickly absorbed several hundred dollars worth of linseed oil.

When we showed up to help install the finish coat of earthen floor plaster, David and Maureen had already prepared all of the ingredients.  The photo below shows all of the materials required for one batch of finish floor plaster.  Two buckets of clay slip, each made by mixing 2/3 to 3/4 bucket of finely sifted clay from the site with enough water to cover, mixing with a paddle mixer, then sifting the resultant slurry through a fine screen into another bucket.  Three buckets of fine masonry sand.  One bucket of sifted red sand from a sand dune near Moab, Utah.  A small amount of straw to give color flecks to the finished floor.  A wheelbarrow and shovel for moving materials, and a small, electric driven cement mixer.

Materials for one batch of finished earthen floor plaster

The next photo shows some of the tools we used to apply the floor plaster.  Hand pump mister bottles to dampen the subfloor before plastering.  Heavy carbon steel pointed trowels to initially apply and roughly level the plaster, and rounded, stainless steel "pool" trowels to do the final leveling and smoothing.  The sponge is used with a bucket of water to frequently clean mud off the trowel as you work.

The next photo shows Doni Kiffmeier and Kaki Hunter, authors of the book, "Earthbag Building", applying finished floor plaster.  It took awhile for the rest of us to have the courage to try this.  At the start it was frustrating and seemed very difficult to get a result that looked anything like what Doni and Kaki could do so easily.  By the end though, we all were plastering like pros (or so we thought).

  It took us two days to plaster the 1000 square feet of so of floor.  Here's a picture of the result:

The finished floor, still wet

At this point, David and Maureen headed off to go Elk hunting, and the rest of us headed home.  The next step for this floor would be to do a finish troweling when the floor is "leather" hard, then a light sponging with a grout sponge to expose the bits of straw for color.  Finally, the owners will apply seven coats of linseed oil, each coat cut with greater amounts of non-toxic thinner, to allow it to penetrate.  The final coat gets mixed with beeswax for a water-proof, fairly durable finish, and rubbed in.  The final finish may need to reapplied every year or two.

We're looking forward to seeing how the floor comes out when we go back up in December (we're signing up to caretake at an elk and bison ranch in the area).  We're told that the floor will have a slight give, unlike concrete, and with the slight waviness caused by hand troweling, will have some texture that also feels good to walk on.  The home is a passive solar design, with large, south facing windows that let in the low angled winter sun.  The floor will absorb the Colorado winter sunshine, and be warm to walk on.  It should be nice!