by Athena and Bill Steen - Cohabitat

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Perlite (or vermiculite)/light clay Perlite is mixed with a clay slip, either by hand or with a concrete or mortar mixer. Enough slip needs to be added so that the perlite binds together and that the mix has sufficient density. Like most facets of the earthen floor making process, experimentation will be needed to yield the proper proportions. Pumice fines (or other lightweight volcanic stone) can most likely be laid dry and tamped for good compaction. The Sub-Floor The finished earthen floor, needs to rest on a compact, level surface. If an insulating and/or drainage layer has not been used, the sub-floor can be nothing more than the well-compacted ground. Otherwise, 2 to 3 inches of compacted silty/sandy soil (not pure sand) can be applied over the insulating or drainage layer to insure a solid base. This soil needs to have enough day that it holds together when dry. Slightly moistening the soil will help the initial compaction. The sub-floor can serve as a good working surface during the final construction stages of the building. Foot traffic will help compact the bottom layers. Radiant floor tubing can be installed into this sub-floor layer. Finding a Soil Mix for the Finished Floor Layer Determining a good soil mixture, a combination of clay, sand and fiber (chopped straw), is the most critical step of the finished floor layer. The mixture needs to have sufficient clay to bind all the ingredients together with good strength. Conducting a series of tests using varying proportions of these ingredients, is a crucial step. The strongest earthen floor is one that doesn't crack. Cracks, even when filled or grouted remain the weakest and most vulnerable part of the floor to damage. Creating test samples to see how they dry is crucial. Analyzing soil for clay content To determine whether or not soils contain enough clay to be used for a floor, several simple tests can be done. One is to form the moistened soil into a round egg-sized ball using just enough water to bind it together without it sticking to the hands. Let it drop. If it breaks easily there is most likely not enough clay content. If it resists breaking and has a sticky adhesive quality, the clay content is probably sufficient. The same ball can also be cut in half with a knife. A shiny surface on the soil reveals clay while a dull surface indicates silt Another indicator is that clayey soils resist penetration of a knife while silty/sandy soils show little resistance. Handling and feeling different soils and noting the differences between them will begin to reveal a lot about them. With a little experience you will have a natural sense about what generally needs to be added to correctly adjust the soil.
Mixing Test Samples for Finished Floor To find a mix for the finished floor, the soil being used needs to be tested first alone and then sit h varying quantities of sand and/or straw. Both the soil as well as the sand should be sifted through 3/8 inch hardware doth to remove any larger particles, debris and stones. Mix enough material to create test samples that are approximately 1/2 to 1" thick and 12* square Clay soil by itself Mix with water without sand or straw Clay soil and sand Dry mix different proportions of soil and sand Add increments of sand: 1/2 part sand to 1 part clay/soil 1 part sand to 1 part day/soil, etc. Continue up to 3 parts for starters. Add enough water to thoroughly blend alt the ingredients. The mix should be kept as dry as possible and yet remain workable. These samples should dry in the same place where the finished floor will be installed. Make sure the samples are marked with their appropriate percentage of clay and sand. When dry, choose the sample that has no cracking and has sufficient strength. Too much sand will produce a weak floor. If by chance, none of the samples are free of cracks, the soil being used may be unsatisfactory because of the expansive nature of the clay. If the crack-free sample lacks adequate strength, it is then necessary to work backwards. Select several of the samples that seem to have good strength and start over by remixing them but this time with straw. Begin by adding 5% and continue in increments of 5% up to 25%. When dry, observe to see if there are any samples that are crack-free and that have good strength and density. Too much strew may yield samples that lack sufficient density for a good floor The straw used should be finely chopped (straw passed through a 1/4" or 1/8* screen). Clay soil with straw Another option is to mix the clay soil with only straw and no sand. In this case the concentration of straw will need to be higher than if sand were added. As above, add straw in increasing increments, 5% at a time This approach has value when sand is difficult to come by or is an added expense when money is scarce. With such a high quantity of straw added, there may be more difficulty achieving enough compaction and strength. Sanely soils There are some soils that are too sandy or silty by nature and lack sufficient clay to produce a good floor mix. There are basically two major options in this case. Either additional clay can be added to bring it up to a suitable level or a small amount of portland cement (6 to 10%) can be added. Cement is probably the most commonly available stabilizer for sandy soils. Straw can also be added for effect, if wanted, to any test sample that produced good results without it. Once a mix has been selected, a larger test sample (a square meter) can be completed for final confirmation.
Page 1 and 2: y Athena and Bill Steen illustratio
Page 3 and 4: Earthen Floors an introduction Eart
Page 5: Insulation For insulation, 4 to 6 i
Page 9 and 10: Applying the floor mixture is most
Page 11 and 12: The second layer Optimally; the sec
Page 13 and 14: Earthen floors can be divided with
Page 15 and 16: Periodic Applications of Coat 4" ca
Page 17 and 18: Yavapai Sports Surfaces P.O. BOx 17

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