I was so very excited to hear about Kevin McClouds new four part TV series – Man Made House. Its a show that combines many of my loves. Kevin McCloud, building an off grid cabin in the woods.

Kevin’s show: ‘Grand Designs’ first peaked my interest in owner built homes and put the idea of someday building my own firmly in my head. (Ben Law’s Grand Design was a big turning point in how I viewed the home, what it should be made from and how it should fit into the landscape!)

I’m really glad that this show is touching on off grid living, alternative energy sources and recycled/reclaimed materials. It’s definitely a humorous approach, using wacky techniques. But as the cost of oil rises these are becoming more and more viable options.

Having laid several earthen floors and being a huge advocate for them, I am really excited to see the inclusion of an earthen floor in the cabin.

On so many levels earthen floors are pleasing to me:

  • Having a large earthen mass as your floor means that during the day, the floor will be storing heat from the sunlight that hits. As the temperature cools off overnight the floor then releases the heat back into the room. This acts to regulate the temperature in the room, keeping it cooler during the hot days and warmer during the cold nights. The analogy of a rechargeable battery is often used. (for more information on this thermal mass effect read here)
  • The feeling of walking on the floors is another big draw for me, it’s warmer than concrete and can be textured or smooth depending on the finish you are after. Without getting too hippy about it, it feels like a connection with nature.
  • But the most appealing part of earthen floors, is that you have most, if not all of, the materials right on your building site. You probably dug out most of what you need when you dug your foundation, making them very cheap.
    It’s quite literally, dirt cheap. (ho ho!)

Most earthen floors are a mix of sticky, aggregate and fibre. This is usually clay, sand & straw.
Something that sparked an interest for me was the inclusion of raw milk in the floor mix. This may seem a bit of an odd inclusion, but Casein is often used in earthen plaster mixes. Casein is milk protein and can be used as an additive to clay plasters or various paints to strengthen and prevent dusting.
Casein makes up about 80% of the proteins in raw milk so it makes sense why mixing in the raw milk would provide a good floor strength.

It was a shame that the possible reasons for the floor cracking were not mentioned. It was left as a bit of a failed experiment, when actually with a couple of small changes the floor would have turned out beautifully.

The mix that Kevin used would most likely have turned out perfectly for a thin finish coat. The lack of any sizable aggregate when pouring a floor 4 inches deep would lead to cracking alone. Kevin used chalk as an aggregate, which is a very fine powder. A better material would have been masons sand with it’s larger particle size. (for a base pour, then going to the finer aggregate for the finish coat)

The amount of clay binder (This is found naturally in the sub soil he dug up) in a floor should be somewhere in the 10-15% range.
The mix that Kevin used was 1 part sub soil to 1 part chalk, which could well be the right ratio based on the clay content of his sub soil but was not discussed.

You can test the clay content by performing a shake test, or simply creating a few test batches varying the amount of aggregate you add. If your test samples crack, there is too much clay. If they crumble or are dusty, then there is too much sand.

The steps to finishing an earthen floor that make it waterproof, mop-able and tough are to oil it, using linseed oil or similar. This forms a crystalline structure in the floor as it sets and provides a tough top layer. Then applying a wax layer will provide extra protection.

I hope the show revisits the floor in the last 2 episodes, it is a great opportunity to bring the idea of earthen floors to the masses, it would be a real shame to present it as an old failed method, when in actuality when done right it provides a fantastic, vernacular floor system that costs next to nothing.