Plaster Testing:

     Ingredients

     Test batches

Applying Plaster:

    Techniques

    Case Study

Earthen plasters have three essential components: sand, clay, and fiber, which can be mixed in any number of combinations.  Common ingredients for creating a good plaster and a few helpful details about them are listed below:

Sand- Sand is an essential ingredient for any earth-based building material as it provides the structure and thermal mass to the mixture.  Beach or round sand does not work as well as sharp, blocky sand grains.  The sand should be screened to remove large objects and create a uniform texture in the final plaster.

Clay- Clay is another very important ingredient that holds the material together like a glue.  If you will be using soil found at your own site, you will need to perform a soil test to discover what ratio of sand, silt, and clay you have.  The clay should be screened to a reasonably fine consistency and then wetted and stirred until a slurry is formed.

Straw- Straw will work as the fibrous component if it is chopped finely enough.  Otherwise your plaster will not be smooth.

Cow Manure- The manure must be fresh (wet) and should be wetted until in a slurry form.

Horse Manure- The horse manure must be dry and screened to remove large chunks.

Paper pulp-  The pulp is created by stripping newspaper into small ribbons and soaking it in water for at least 24 hours.