The making natural paint series (part 3) Earthen plaster

gogreenbuddy (66)in #homesteading • 7 years ago (edited)

It's not a paint but I write it so I make the rules:). I've never used earthen plaster but I have experience with cob and used earth rendering to fill gaps in a log floor. I was really surprised how much better it is than just cement or brittle commercial plasters. The biggest benefit I think is that if a corner of the plaster chips away you can really easily repair it with earth. In the case of a commercial plaster you need to buy a new package because the old one isn't good any more. That stuff doesn't store well..

When is earth a good choice?

I'm quite a fan so I'm gonna turn the question around to 'when isn't it a good choice?'. Earthen plaster has some drawbacks just like cob. It doesn't stick well on cement walls, smooth walls or painted walls. The best is a wall made out of straw, cob or old rough porous brick.

There is no chemical drying process, but a water based process. This sounds like a good thing but it makes it a little problematic in rainy & windy climates. In The Netherlands were you've got rain and wind at the same time you need to make a special design to make earthen work. The lowest 30 to 50 cm of an outside wall can't be earthen plaster because this stays wet too long. If the roof has a little overhang the walls can get moisture issues. This can be fixed with applying a waterproof layer over the plaster.

The second and last big drawback is earth requires much heavy labor. It's maybe cheap, healthy and pretty, but the work is back breaking and it will dull very fast. A big group of people to get this job done fast is really helpful.

Earthen plaster recipe

The recipe requires a good amount of prepping. I already warned you about how labor intensive this is. So you can cancel your fitness subscription and throw out of your TV. You won't need them anymore.
Start with collecting the material. This can take a while you can't really go to the shop for a half a bucket of crushed cow manure. Calculate how much you need. The below recipe is for roughly 10 M² this number will greatly vary depending on how smooth the wall already is.
Start sifting the sand and (very wet) clay to get the rocks and wood out. Now make a test batch and apply it to the wall. Check how well it sticks to the wall when dry. If that is a success continue to make a big batch!

I like to crush the cow manure to a powder but it is also possible with fresh manure or cow manure in a wet bucket. Crushing isn't essential. If you don't like the idea of manure in your hands or the smell you can cut it out of the recipe for inside use. The micro fibers and enzymes strengthen the plaster. The smell will go away when the plaster dries out.

You need another fiber source. Animal hairs are the best. You have to ask a dog, horse groomer or a farmer that grooms the cows. Plant fibers are possible too cattail fluff, dried grass clippings and
cotton balls.

Recipe for 10 M²:

3 buckets of sifted sand
3 buckets of sifted clay
½ bucket of fine crushed cow manure
Fiber source short hair.
Strong screen sift
Big tarp

How to make it

Spread the tarp on the ground and throw all the clay and sand together. Start stomping and walking on it with bare feet to mix it. When it's homogeneous you add the cow manure. Spread the hairs evenly over the whole mix and start stomping it again with your feet till it's smooth.

Other great options with earthen.

Earth isn't only great to make plaster. You can make whole cob houses from it, earthen stamped floors, It's a great thermal storage, cob furniture, earth bag housing, and cob wall art are all possible. I collected some picture to show the possibilities I include the source so you can check up their websites.