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MIXING & LAYING AN EARTHEN FLOOR
We laid an earthen floor for our kitchen in a new build cob house. We were inspired to do this after working with and seeing earthen floors Bill & Athena Steen of The Canelo Project make in Arizona. We also felt this type of floor would be in keeping with a cob house. The materials used such as sub soil (with clay content), chopped straw, sand and lime are all sustainable.
There are some problems with using earth or sieved cob for flooring in this country, the climate is not dry, hot and sunny as in SW United States therefore the drying time can take weeks. However this can be overcome with the use of dehumidifiers and slow drying of earth will not crack too much. Nevertheless one must accept that there will be a certain amount of cracking and shrinking.
The floor laid for the cob house was approximately 40 sq. m so it was important to have as much mechanisation as possible. We estimated that approximately 4 tonnes of sieved sub soil would be required therefore we arranged for the sub soil to be screened at a local quarry.
The soil, with the other ingredients, was mixed dry in a cement mixer. Adding water to the mixture in a cement mixer tends to make the material stick to the sides and not blend together very well. The dry mix was tipped onto a concrete slab and mixed with a rotavating type mortar mixer.
To acquire the right mix for an earthen floor it is important to make test panels using various ratios of sub soil, chopped straw, coarse sand and possibly a small amount of lime. After making several small panels, about 400mm x 600mm, we made a large test panel of about 2m x 1m to ascertain how strong the floor would be and how much it would crack.
To lay the floor we divided it into four sections to make manageable areas. The mix is tamped down and compacted. This was at 50mm depth, checking all the time that the finished floor level was the correct height to the datum line. To ensure the levels were correct throughout we used a large length of timber placed on wooden ‘rails’ pulling it over the earth mix to create a level floor finish. To check the floor is perfectly level it is important to use spirit levels at regular intervals.
When the whole floor was laid a power float was used to achieve a smooth finish. For a small area it is possible to float the floor with a flexible hand trowel. As the floor dries cracks appear these should be floated either with a power float or by hand. We used a garden water sprayer to damp the floor while floating. A small quantity is needed in order to bring the ‘fat’ to the surface.
A large floor area takes about 6 weeks to dry out, if weather conditions are good, that is dry, bright and breezy, considerably longer if cool damp conditions prevail. It took four people 7 working days to mix and lay the floor. Laying an earthen floor is slow and labour intensive.
When the floor dried out it had to be sealed with linseed oil and turpentine. The first coat was pure linseed oil then subsequent coats of oil and turpentine, increasing the amount of turpentine for each coat was applied. This ensures the oil mix penetrates into the floor rather than creating a crust on the top. We used about 12 coats, until the floor reached saturation point. The easiest way to apply the coats is to use a soft bristle broom with a plastic storage box as the container for the oil and turpentine. The final floor finish is a natural hard resin oil.
The finished colour will always become much darker than the colour of the earth used. We used a red soil from the Crediton area but the finished colour is a deep red/brown shade.
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Red sieved earth to be mixed with sand and chopped straw |
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Adding water to the mix of soil etc, mixing on concrete slab with mortar rotavator. |
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Tamping and compacting mix, note levelling guide rails. |
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Using a power float to smooth finished floor. |
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This is the finished floor
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