But it covers the ground. In July 2010, seven students gathered from the U.S. and Canada to learn the art of the earthen floor at Aprovecho. Taught by earthen floor expert Sukita Crimmel (www.sukita.com), the students spent three days with their hands in the mud installing and finishing floors of clay, sand, and straw.
The first day we assessed our on-site clay, generated an appropriate recipe, prepared the room and installed a 375 sq. ft. base layer appropriate for radiant floor heating systems. Students got a lot of hands on practice under Sukita’s guidance with the tools and techniques. We followed up the next day with a one inch thick finish pour in the downstairs of Aprovecho’s middle cabin. The team was inspired and worked late into the afternoon in hopes of finishing the 350 sq. ft. space. A finish layer takes a little more patience and technique to get it smooth and flat. After finishing the floor on the third day the class went over burnishing techniques and the application of the finishing oils and wax. Three months later the floor is hard, beautiful, and standing up well to the temperament of a two year old.
We learned a few things during this Earthen Floor Installation/Training. After installation of the finish pour there was some noticeable cracking. We used the same recipe for the finish floor that we have been using for our earthen plaster walls with great success. Why, then, would cracking appear on the floor if it hasn’t on the wall? Due to the “keying in” of the plaster with the gaps between the lathe on our walls, the plaster wall system may be better equipped to handle the shrinking properties of the clay. Also, we do not apply plaster layers more then 3/4 thick at a time whereas the finish pour on the floor was one inch thick. I don’t offer these reflections as definitive answers but possibilities. Either way, the conclusion is to increase the proportion of sand in our earthen floor mix. After repairing the cracks with screened floor mix, the floor has stabilized and is holding up great.
The other hiccup during the workshop was the discovery of a “bouncy floor.” The sub floor, consisting of tongue and groove 2×6, moved noticeably when jumping up and down. This was a concern for the long term integrity of the earthen floor. Because the problem was widespread we decided to cover the floor with 1/4 inch plywood which evened out the bounce. The way to avoid this problem in the future is to ensure your floor joists are properly spaced in relation to your sub-floor.
All and all, the workshop was a great success. Some of the class will be taking their new abilities back to their natural building contracting business while others will be using their skills in the service of their own home. Here at Aprovecho, we have been impressed with potential of the earthen floor and look forward to installing more in the future!