How To Plaster Walls: Natural Clay Plaster Finishes

November 19, 2008

Earthen plasters provide a beautiful, soft, and an organic finishing touch to your home, whether they be a straw bale house, cob building, wood cabin, or even plain old sheetrock walls. A simple natural plaster can be mixed from ingredients straight from the earth, including sand, clay, and fibers such as straw, cattail fluff, or even cow manure.

It’s a simple process and a creative one, too: you can let your imagination shine through earthen plaster with its vast sculptability and its variety of application.

Read on to learn more about making and applying earthen plasters!

How to make clay plaster

A natural earth plaster is composed of three main elements, typically sand, clay, and fiber.

  • Sand provides structural strength and makes up the bulk of any earthen plaster mix. Fine, sifted sand is used to provide a smooth finish without small stones or pebbles to interfere in the application.
  • Clay is a binding agent which helps to make the earthen plaster sticky and adhesive. Clay is typically soaked and mixed to break up larger chunks before being mixed with the other ingredients. Your earthen plaster’s color may be determined largely by the color of your clay. Local clays come in a wide variety of colors.
  • Fibers such as short, chopped straw, cattail fluff, or even fresh cow manure are common and important additions to earthen plasters. Fibers help make the plaster strong and resistant to cracking. Manure is the fiber of choice of many traditional peoples (and many modern natural builders, too), and for good reason: the fiber content and enzymes make for a very strong and durable plaster mix. (And to set the record straight: once dried, earthen plaster containing manure does not have an odor. Also, it’s actually really fun collecting cow pies for plaster. Try it!)

Additional additives such as wheat paste help increase durability and stickiness. These ingredients can be mixed by foot on a tarp, or with a hoe in a wheelbarrow.

An earth plaster recipe

The ratio of these basic ingredients may differ depending on the quality or type of materials that you choose to use. I can provide at least one recipe that I have recently used that has worked well for my cob house.

  1. 3 parts (that’s three five gallon buckets) sifted sand (sand sifted through a 1/8″ screen)
  2. 1 part soaked clay
  3. 3/4 part cow manure
  4. cattail fluff (to taste)
  5. 8 cups wheat paste

Applying earthen plaster

Earthen plaster can be applied by hand or with a trowel. Depending on the evenness of your wall’s surface, you may choose to go either route. The final mix should be soft, sticky, and wet, and it should hold readily to your (pre-soaked) wall. Add small amounts of water if your plaster seems difficult to spread on your surface.

Take the opportunity to experiment with your plaster and try making different shapes and forms. You can even embed mosaics directly into your plaster using smooth, broken glass or ceramic bits. (Save those broken dinner plates!)

Once your plaster has had some time to dry (but has not dried completely), you can make an even smoother finish by buffing the surface with something like wet burlap or a small sheet of rubber. Go in circular motions to work out rougher areas. You’ll be amazed by how much smoother your wall is after this simple process.

A low impact finish for your home

Earth plasters are very beautiful, smooth, and soft, and can give your home a very warm and inviting ambiance. They are an obvious choice for straw bale houses or