Last Updated: Jul 10, 2021
Do you have an aversion to dirt? Our modern society seems to: parents tell their young children to stay away from a mud puddle, we walk out of our way to avoid getting our feet dirty, our cities and towns have gradually become concrete jungles, with most green areas paved over to help us avoid the bother of dealing with dirt. But don’t write off dirt so quickly…it could be a primary ingredient in your next floor!
While the thought of mud floors is usually associated with impoverished households of the Third World, poured adobe floors (and yes, we are talking about floors made from dirt) offer a beautiful, natural, environmentally friendly flooring alternative that is dust-free, durable, and extremely comfortable.
Sealed, dirt floors have been around for thousands of years, and continue to be common in dry areas, such as the desert southwest of the United States. Essentially, poured adobe is a mixture of clay, sand, straw (or some other type of fiber) that is mixed to a semi-liquid state with the addition of water, poured over a base layer of the subfloor, and then sealed with some sort of oil and/or wax to harden the floor and keep it from becoming dusty.
It is important to get the right proportions of clay to sand, as mixes with high levels of clay content will be prone to cracking, while mixes with too much sand will become dusty over time. The addition of straw or other sources of fiber help to hold the mix together and form a continuous connection throughout the entirety of the floor. The mixing process of clay, sand, and straw can be done by foot or with the help of a small concrete mixer. Linseed oil is the most common type of oil used for sealing the floor, though traditional techniques relied on oxblood or wheat paste (wheat flour mixed with water) to harden the floor.
Poured adobe floors offer a number of important benefits. Because they are made from local materials, there is no factory pollution associated with the production of these floors. The ecological performance of this natural flooring alternative offers optimum health benefits, as it is completely free of toxins. Other common benefits associated with poured adobe floors include the following:
Most of the flooring alternatives available to homeowners today rely on heavy, dense materials that are sourced and manufactured at great distances before being shipped to the building site. While there are sustainability certifications for wood flooring, and cork flooring is making a comeback as a more sustainable flooring alternative, poured adobe floors are perhaps the only flooring alternative that can be sourced, manufactured, and poured directly from the building site. This allows poured adobe floors to approach a zero embodied energy footprint, limiting the carbon emissions associated with this flooring alternative.
Earthen floors offer a huge source of thermal mass that can help your home to capture and store the heat from the sun. For homes that have incorporated passive solar design, an earthen floor can help to capture and store enough heat to keep homes warm during cold winter months.
Around 548 million tons of construction and demolition debris was generated in the United States, in 2015 alone. One of the most important objectives of sustainable building practices is to reduce waste and pollution. While old tile floors, wood floors, and carpets are hard to recycle and often end up in landfills, a poured adobe floor will simply decompose back into the soil through the work of rain and microorganisms in a cyclical, biological process.
The average cost for hardwood floor installation is between $6 and $8 per square foot. Poured adobe floors, on the other hand, can cost a fraction of that expense, and can also be completed by homeowners looking for an intriguing DIY project. While a DIY poured adobe floor can be “dirt” cheap, hiring a contractor can lead to expensive labor costs, as the process of laying a floor can take time. However, if you have a good source of clay on your land, materials can be essentially free.
Unlike other types of flooring alternatives, poured adobe floors contain absolutely no formaldehyde, asbestos, or other volatile organic compounds (VOCs) that can lead to health issues. The earth itself is a natural air filter, as microscopic pores in the soil allow the floor to breathe. In essence, a poured adobe floor can help to keep the inside air fresher and free from allergens, especially when several layers of foundation gravel are laid to improve drainage and avoid any issue with mold or mildew buildup underneath the floor.
To begin, you will need some sort of barrier that will separate your floor from the soil below. If there is a concern that radon gas might leak into your home, you should certainly invest in a plastic barrier, and/or install a vent to exhaust the fumes outside. On top of that barrier, several inches of pumice or perlite is a good alternative to gravel, as this also adds insulation benefits. Rock wool or insulative blue board can also be used for part of the barrier to increase the R-value of your floor.
Once you have the barrier laid, you will need a 3 to 6-inch subfloor. Road base is a good option. If you can’t source road base, you can make your own by mixing gravel with sand and clay. Tamp this mix as you lay it on top of your barrier, as this will offer structural strength, a solid foundation, and added thermal mass to your floor.
Next, mix your poured adobe, taking into account the correct proportions to avoid cracking and give the aggregate maximum strength. Ideally, you will want your mix to contain around 15-20% clay and 80-85% sand. It is important to experiment on a 2 foot by 2-foot square to see how the mix dries. If cracking is present, you will need to add more sand and straw. If the mix is dusty, consider increasing the amount of clay in your mix. You will want to lay the mix in a maximum of 1-inch layers, and if cracking does occur, it might be necessary to lay 2-3 layers of the mix, letting the previous layer dry over a period of several days. A masons trowel is used to create a smooth finish as you lay the floor.
Once your poured adobe floor is laid and dried, linseed oil can be applied to the entire floor with a rag to help “seal” the floor. Raw linseed oil is the most natural option, though it takes much longer to dry. Boiled linseed oil might contain some solvents that can create an unpleasant odor in your home, though it does dry much more quickly. For maximum sealing, you might have to lay down several coats of linseed oil. Melted beeswax can be added to the final application for another natural sealing option.
Once the linseed oil and beeswax has dried, your poured adobe floor will appear almost like leather. The floor will be hard, can easily be swept and mopped, and shouldn’t be dusty. To protect a poured adobe floor, you will want to place a few pads underneath the legs of chairs and tables to avoid scratching. If dents or scratches do occur, you can simply mix up a bit of poured adobe to repair the part that was damaged.
While poured adobe floors require thinking a bit out of the box, they can also offer a natural charm to your home. For creative and artistic homeowners, experiencing with different colors of clays or adding natural pigments can allow for a beautifully colored home interior. Living in a home with a mud floor has never been so appealing.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.