Earthen Floors: Why, How & Where
Guest Author’s Note: My name is Ashley Lubyk. I’ve been running Dirt Craft Natural Building for the last five years, and have had the great pleasure to work with Verge in many capacities, including guest teaching at numerous PDC’s, and even taking my first PDC with them 4 years ago. I’m pleased to have the opportunity to share some of my experiences from the world of natural building here today.
My first step onto an earthen floor (sometimes called a ‘poured adobe’ floor) awakened me. My toes immediately curled to caress it, to feel its leathery softness. The surface was hard but soft at the same time – somewhere between polished concrete and an well loved hardwood floor. I gravitated to a spot illuminated by the sun. The warmth penetrated through my feet and into my belly, and a smile washed over me. The texture and colour was beautiful; it felt alive, and in turn made me feel alive and grounded.
Instinctively I understood that an earthen floor made sense but somehow it defied logic…and I knew it was something I needed to investigate further. Over a period of years of researching, hands-on learning, and eventually installing earthen floors, I’ve come to see that they are a wonderful and viable alternative to a wide-range of flooring types, and in a lot more situations than I initially thought. And yes, they can even be installed over a wooden subfloor…on a second story…in the most conventional of homes…even a home in the suburbs!
Earthen Floors Today
Don’t be fooled, a modern earthen floor is not the dirt floor your prairie ancestors would have lived on. They are not the dusty, crumbly dirt floors found in the imagined ‘mud huts’ of the world. Today’s earthen floor is carefully crafted with special attention given to the final surface, then impregnated with a blend of oils and waxes that impart durability, abrasion resistance, yielding a smooth and luxurious surface. It’s the kind of floor that draws people, especially conventional contractors, to their knees to gain a closer look. They rub it as though it will grant them a wish. Intensity emanates from their eyes as they ponder how it is that the surface before them could be made from simple ‘dirt’.
Earthen floors are a welcome escape from ‘standard’ flooring types, many of which are mass produced, energy intensive and toxic to manufacture, destructive to habitat, and, as is often the case, expensive and difficult to maintain. And because the materials needed for an earthen floor are widely distributed across our planet, they can be gathered or dug directly from or close to the land around us. They require no special processing and can be mixed and installed by hand. This intimacy with the material allows a direct connection to the earth in a whole new way, all the while creating a surface that is comfortable, attractive, and relatively easy to install and maintain. And even if the material is mixed by machine, the embodied energy of an earthen floor is a fraction of any other flooring type.
Another huge upside of working with earth is that it invites play and creativity, presenting countless opportunities to personalize the final look and feel of the floor. Tiles, rocks, flagstone, or even tile mosaics can be inlaid into the wet earth to add character and durability. Embedding a grid of wooden forms makes for an interesting floor, lending a more varied surface than one might get with a continual pour.
Practically speaking, earthen floors are a wonderful alternative to a concrete slab and pair well with in-floor heating and passive solar design. The thermal capacitance of earth is similar to concrete, meaning that it has the capacity to store and release heat in winter, while remaining cool when summer temperatures soar. Like concrete, when earthen floors are strategically placed – such as in front of a bank of south facing windows – the floor acts as a large thermal battery, releasing the stored heat as the sun fades away. When made part of a well insulated building, this can drastically reduce the required heat load to keep you warm in winter and cool in summer.
How to Make An Earthen Floor
Earthen floors are a simple combination of clay, sand, straw, and sometimes manure. Typically the ratios are about 15-20% clay and 80-85% sand. Straw is thrown in to provide tensile strength and to reduce cracking. Manure can help with workability, but is not essential. With each new clay we spend many hours evaluating and testing recipes to ensure that we get a good, strong mix.
Clays vary from place to place, ranging from browns and yellows to reds and greens. Most often it is the colour of the clay that determines the colour of the floor. Of course natural pigments can be added to alter the colour, but this will always require some experimentation. In all cases, oiling process tends to darken the final colour, so creating a very light-coloured earthen floor can be difficult. It is also possible to add what is essentially a clay paint to the final surface to impart the desired colour (this reduces the amount of pigment needed). This may be brushed or troweled onto the surface. Each creates a different and unique texture effect.
Earthen floors are usually laid in wet and levelled using a combination of screed guides and screeds or, in some situations, a laser level. Once the desired thickness is attained, and the tiles, rocks, etc are laid in, the final surface is trowelled to a smooth finish. A day or two later the semi-firm surface is further ‘compressed’ to further unify the surface. Once compressed the floor is left to dry; this can take a week or more (fans or dehumidifiers or open windows aid the drying).
Once dry, any cracks or pockets can be filled with more floor material and then the clay paint can be added to create a more varied surface or to add a different colour. We’ll often ‘skip trowel’ this layer on to create a slightly mottled, varied surface that is smoother and more polished floor. This treatment is then allowed to dry.
Once completely dry, the final surface is finished with 4 to 6 coats of oil, often hemp or linseed, then topped with a combination of soft waxes. Once dry his final layer can then be buffed to give it a wonderful sheen.
Where They Work
Earthen floors can be installed anywhere a concrete slab or tile floor would be, so long as a solid base is provided. The success of an earthen floor relies on substrate conditions and this will ultimately guide the preparation of the subfloor. Ground moisture (including high water levels) and extreme cold must be factored in to create a floor that remains dry and comfortable, avoiding the use of excess energy during the heating season.
The process of getting the final finish follows the same pattern – the finished earthen floor surface is typically 3/4 to 1” thick, and where necessary, with one or more additional layers below.
Where earth is placed over a wooden subfloor, some considerations must be made. It is common that the earthen floor would be installed at 3/4” (the thinnest we install earthen floors) to lessen the overall weight bearing on the subfloor. The critical thing here is not only the weight of the earthen floor material, but to make sure the subfloor is reinforced to the same standard as if you were to be installing tile, L/360. This is a measurement of deflection and means that the floor mustn’t flex more than 1 inch over a distance 360 inches (or 1/3 inch in 10 feet) when a dead load of 300lbs is applied to the middle of a floor joist’s span. Span tables are available to make easy work of this math without having to hire an elephant to stand on your floor. An additional layer of 1/2” of plywood is generally laid perpendicular to the existing 3/4” subfloor (not unlike tile), and generously screwed together with deck screws. A tile underlayment is then installed over the subfloor to keep water from impacting the wood below. At 3/4 inch, an earthen floor weighs 7.5 lbs/sq ft, which is comparable to some of the heavier tiles out there.
Where an earthen floor replaces a concrete slab on grade, the earth is built up in a series of layers, typically from 4 to 6 inches thick. A coarse base layer is laid to bulk up the floor (serving as stable layer to work on as a house moves toward completion), with a more refined finish layer applied toward the end when finishing work is occurring. In some cases the base layer is poured in wet and left to dry, while in other cases it is installed as a relatively dry layer and tamped. How one chooses to proceed is largely a matter of preference or, as is usually the case, dependent on the building schedule.
Earthen floors also work well with in floor heating. The radiant tubing is laid then incased in the earthen floor mix. We’ve applied in floor heating in both insulated earthen slabs (often within 4 inches of material), as well as over a wooden subfloor in 2 inches of material.
We’ve also been hired to install a thin layer – often 3/4 inch – of earthen floor overt a supposedly finished concrete floor ‘soften’ the surface. These clients wanted the ‘thermal mass’ benefits of the concrete slab but after having lived on the concrete for a period of time were disappointed at how hard the concrete was on the body. The results have been fantastic and, from our clients perspective, less draining on the body than concrete or tile.
Where Earthen Floors Don’t Make Sense
Bill Steen, one of my early teachers, says that one of the most misunderstood aspects of earthen floors is that they are unrealistically expected to perform in a manner similar to concrete. While an earthen floor can be made to be durable and serviceable it is not a concrete floor, which has a compressive strength ten times greater than earth. This is not to say that earthen floors are inferior, only that concrete may be overkill in many situations. I believe concrete has it’s place but because it is very energy intensive to produce, it should be used sparingly and only where the strength and durability is absolutely needed.
As such, we discourage earthen floors in high water areas and areas that receive a lot of abuse (you probably wouldn’t put an earthen floor in the garage, for instance). We generally also dissuade people from putting earthen floors in flood-prone basements or utility rooms where a compromised hot water tank could lead to a muddy mess. Mud rooms or bathrooms with bathtubs with children prone to spontaneous water fights may be asking for a more water tolerant surface like tile.
Use and Maintenance
A well cared for earthen floor should last a lifetime or longer. Any floor will wear and the rate of wear is a dependent on how the floor is used (the activities that the floor is subjected to) and to the degree that it is cared for (the maintenance schedule).
To get the maximum life from the floor it should be treated like a hardwood floor. While the surface is relatively durable, it is susceptible to scuffing and gouging. Felt pads on the bottom of furniture is a good idea to keep the floor looking great.
As was said above, wet and muddy boots are probably best kept off the surface as a general practice, but if the floor gets dirty or if someone spills their juice the oils and wax seal the floor such that it can be lightly mopped and wiped to maintain cleanliness. Frequent mopping will strip the oils, while re-oiling/re-waxing the floor on occasion will keep it looking its best. And though we’ve never taken our floors to this extreme, there is an old folk saying that goes something like this: “A well loved earthen floor is oiled once a day for a week, once a week for a month, once a month for a year and once a year for life.” It might not be necessary but it certainly wouldn’t hurt!
A Floor For Life
Earthen floors are a wonderful alternative to more energy intensive flooring types like concrete or tile and as we’ve seen, can be used in many parts of the home. Earthen floors also play a major part in the natural heating and cooling strategies of energy efficient homes and they can be used in replacement of a concrete slab or to retrofit an existing one.
With a basic understanding of the materials, the surface preparation, and some guidance on installing the floor, virtually anyone can make an earthen floor that looks great, wears well, and is healthy for people and the planet. We offer workshops throughout the year, including a 2-day earth floor workshop in Millarville, AB on June 27th & 28th. Visit www.dirtcraft.ca for more information.