Natural clay finish plasters add an unparalleled beauty to any home, and it was exciting to apply these plasters to Canada’s Greenest Home this weekend.

These skim coat plasters can be applied over any wall surface. In this project, we used them over clay base coat plasters and over drywall.

The plasters are mixed on site using widely available and affordable materials. Clay, sand, calcium carbonate, pigment, flour paste and water are mixed together and applied to the wall by trowel in a single, thin coat (~1/8 inch).

Our typical formula is 10 parts clay, 4 parts sifted sand, 1 part calcium carbonate, 1 part flour paste (a natural glue/hardener) and ~3.5 parts water. Natural pigments are added to this mix by weight, based on trial samples made in advance. As with baking, the dry ingredients are mixed together and then added into the water, flour paster and pigment that have been blended.

The clay in this case is Tile 6 Kaolin, from a pottery supply store. We’ve used other kaolins and ball clays with similar results. Calcium carbonate is finely ground limestone, from Omya in Perth, Ontario. Flour paste is cooked by boiling 4 parts water and adding a mixture of 2 parts cold water and 1 part flour and boiling until thick. Our natural pigments come from Kama Pigments.

Helping us with the mixing and application was our good friend Mike Henry, a plasterer with Camel’s Back Construction. His attention to detail helps bring out the best in the clay plaster.

There is nothing like the depth, richness of colour, sound attenuation and warmth of a natural clay finish plaster!