Making and applying an earthen plaster exterior finish

by ziggy on November 19, 2008 -- 4 comments -- Follow

A week or so ago, while the weather was still reasonably comfortable, I decided to experiment with making an earthen finish plaster. I settled on ingredients and a recipe for my earthen plaster mix relatively easily after talking to others who have done plastering here at Dancing Rabbit in the past.

Earthen finish plaster recipe

My recipe is as follows:

  1. 3 (five gallon) buckets of sifted sand (sand sifted through a 1/8″ screen to remove pebbles)
  2. 1 bucket of mixed wet clay
  3. 3/4 bucket fresh cow manure
  4. cattail fluff (to taste – enough until I could see the fibers in every handful of material)
  5. 8 cups of wheat paste

Applying the earthen plaster

This recipe proved to be a pretty good starting point. It was a very wet, sticky, and fibrous mix that held easily to the (soaked) wall. I applied it by hand to a portion of the exterior wall, and waited for it to dry. Thankfully, the plaster did not freeze at any point, and it seems to have dried relatively easily (despite cold temperatures) and thoroughly with little cracking. The coat is quite thin – straw from the cob wall can be seen poking through most of the wall, but I think I like how it looks.

After the plaster had some time to dry (but before it dried completely), I used a piece of EPDM rubber (just some extra cut off from my pond liner) to burnish the plaster, making the surface even smoother. The results were pretty pleasing.

The left photo is an unplastered wall, and right is a plastered and burnished section of wall. (Click for larger versions.)

earthen plaster - before earthen plaster - after

As of now, the entire eastern and northern sides of the house are plastered with just a single batch of earthen plaster. I will not do any additional plaster work until the spring, once it warms up again.

For some background information on earthen plaster, please check out my latest entry on Green Building Elements: Natural Building 101: How to Make and Apply Earthen Plaster Finishes

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  • Lori

    I see that you used this plaster mixture for exterior. how well does it hold up against the weather? I am building a heated cob bench, do you think this will hold up to heat? if so I’d like to try it on my cob oven too. thanks!

  • So far so good. It hasn’t seen much weathering yet, so it’s a little too early to tell. I expect that this plaster would be just fine for a heated bench. Good luck!

  • dawoodshah

    i want make mud plasting in my home so kindly give reply

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