Jeffrey Hart from the Earthen Floor Company gives us the lowdown on natural earth floors, explaining what the components are, how they are mixed and the process of installing them. He also outlines the benefits and limitations, and highlights what makes them a great choice for an eco home.
Interview with Jeffrey Hart
Jeffrey Hart got into natural building in Oregon, USA, where he was an apprentice of earthen floors expert Sukita Reay Crimmel. He spent five years constructing various buildings and installing earth floors in each of them, before returning to the UK. Although he started out as a ‘generalist’ natural builder, as demand grew, he found himself focusing exclusively on earth floors through the Earthen Floor Company. He credits Sukita’s influence for both the modern earth floor technique and the resurgence of this historic building method.
Earth floors have been used for centuries
Historically many buildings would have had an earth floor just because it was the ground beneath the building. At some point, people realised that cow dung reacted with the earth to make it a harder, more waterproof surface. It was also noted that when blood fell onto the floor of farm slaughter houses it made the earth rock solid, so over the years different methods have been used to make the floors harder and more durable. Sukita developed a way to use linseed oil to seal and harden the clay, making it a lot more palatable for the modern world and the way we live now.
All earth floors have a binder, an aggregate and fibre
Earth floors – also known as earthen, cob or adobe floors – all have a binder, an aggregate and fibre. In Jeffrey’s case the binder is clay, the aggregate is sand and the fibre is either straw or hemp.
The process of making an earth floor is similar to that of a concrete or limecrete floor, but clay’s ability to hold together is lower than lime or cement, which is why linseed oil is added.
“The linseed oil turns the floor from something that’s relatively soft and quite easily damageable, to this hard-wearing, leathery rock.”
Earth floors can be structural or just the top coat finish
An earth floor can serve as a thin finish over an existing concrete, limecrete or even timber floor, or it can be built up as a full‑thickness slab. The minimal approach involves a 20 mm top coat, while the full build‑up typically incorporates foam‑glass insulation, optional under‑floor heating, a rammed‑earth base and a top coat.
Jeffrey’s preferred full build-up
Moisture must be managed to avoid problems
Moisture is a critical concern for earth floors and Jeffrey will use membranes if damp conditions exist and foam‑glass insulation as it acts as a capillary break, preventing upward moisture migration. It is also important that the floor dries out sufficiently before the linseed oil is applied.
Linseed oil is used to cure and harden the surface
Linseed oil is the “magic” component that transforms a relatively soft, clay‑based mix into a hard‑wearing surface. Once the clay dries, the oil polymerises, linking long‑chain molecules to create a leathery, rock‑like finish. Without sufficient oil penetration, the floor remains soft and prone to damage. The oil also imparts the characteristic warm brown hue that many owners associate with earth floors.
The embodied carbon of earth floors is extremely low
Switching from a conventional concrete floor to an earth floor can reduce embodied carbon by roughly 83 % (according to calculations using the BEAM Estimator). The reduction stems from using locally sourced clay and sand, eliminating the need for high‑energy cement, and the floor’s ability to be broken down and returned to the earth at the end of its life cycle.
“It’s about an 83 % reduction if you were to swap like for like.”
It is possible to use clay from your building plot
If you’re digging the foundations of your house and the spoil is clay, one option is to reuse it in your floor. Jeffrey believes this is the ultimate local and sustainable floor, but there are a few considerations. Most important is to test the soil to confirm that it is clay rather than silt, which lacks the necessary binding properties. Tests assess shrinkage rates, strength, and colour consistency. Variability between layers can lead to inconsistent performance, so careful excavation and sampling are essential. Unfortunately, using local clay isn’t necessarily cheaper because of the required testing and processing, so the Earthen Floor Company offers pre‑bagged mixes with clay sourced from reliable brickworks and pottery suppliers.
A lot of the cost is down to the labour
The current rate for a finished earth floor from the Earthen Floor Company is £160 per square metre for the top‑coat package, which includes materials, labour, buffing, and waxing. Prices vary with location because of the extra travel but if money is tight, self-builders can do the final oiling and waxing themselves.
You can’t walk on the floor for a month while it’s drying
Although an installer might be able to cover 10 m² per day the whole floor must be completed in a single day. This means multiple installers coming to site, the number depending on the size of the floor. After the mix is laid, the floor must dry out before the linseed oil is applied. The drying time depends on ambient temperature, humidity, and air flow; heaters and fans can help accelerate the process, but Jeffrey recommends not trying to speed things up too much as there can be unintended consequences. Once dry, the floor is oiled and then left for a further 14 days to harden.
“From install to you being able to use the floor it’s three weeks if everything goes well.”
Underfloor heating works well with an earth floor
Earth floors store heat efficiently, making them ideal for radiant heating systems. The heating pipes are usually positioned between the insulation layer and the rammed‑earth base, though some projects place them higher in the slab for a faster response in properties that may not be used all the time (such as holiday lets). The thermal mass of the earth floor prolongs warmth after the system cycles off, reducing temperature swings and improving comfort.
Repairing minor damage to the floor is quite easy
A well‑installed earth floor would be expected to last at least 30 years, becoming more beautiful as it ages. If you damage the floor, making a dent or chip, it’s actually not too difficult to remedy. By crushing leftover “biscuits” (small pieces of the original mix), mixing them with oil, you can fill the crack. While repairs are relatively seamless, they may be visible in certain light conditions. To protect your floor it’s a good idea to oil and wax it as part of the maintenance cycle; the oil’s polymerisation continues slowly over the years, gradually increasing hardness.
“We make little biscuits from the mix leftovers; they’re used to patch dents.”
It is possible to choose the colour of the floor
The natural colour of an earth floor ranges from earthy browns to greys, dictated by the clay’s mineral content and the colour of the linseed oil. To achieve brighter hues, pigments can be blended into the mix, producing uniform colour throughout the slab. Alternatively, a coloured hard wax applied as a surface finish can modify the appearance without altering the underlying material, though this layer may need to be reapplied every couple of years. Most self-builders prefer the authentic, warm tones, but designers increasingly want something bespoke.
“People are becoming more aware of this material now; it’s no longer just a niche.”
There are lots of reasons to love earth floors!
As natural materials are much more accepted these days, earth floors are seeing a revival. Jeffrey has also been doing his bit to train the next generation of installers. He is trying to make earth floors as accessible as possible as he really believes in them. They look beautiful, they feel incredible under your feet, they soften sounds and are good in terms of carbon emissions.
“And at the end of the product’s lifespan, you can break it all up, chuck it in your garden, and it will break down to be just earth again.”
Find out more
Building Sustainability Podcast
Building a tiny house with natural materials
Earthen Floors (second edition) – by Sukita Reay Crimmel
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