How To Install Earth Plaster Over Straw Bale

Earth plaster has long been a common material used to reinforce, insulate or finish the walls of many wood, stone and straw-like structures. It is especially appealing to the environmentally-conscious because the earth plaster is comprised from natural materials without any chemical processing or preservation.

Due to its increasing popularity, earth plaster is offered commercially. However, if you follow these simple instructions you can save some money by making your own.

What Is Earth Plaster?

The material can be created using several formulas, each of which include a binding agent, a structural component and some sort of fibrous material. A typical formula includes clay, sand and straw.

Additives to the formula can help obtain a certain color or drying hardness. A typical additive might be flour paste, which is made by heating a flour/water mixture, creating strong glue that works as both a binding agent and a hardener. Sand provides greater strength, while dry straw helps hold the earth plaster together.

People settling in the American West during the late 19th and early 20th centuries used available buffalo dung instead of straw as the fibrous agent in the mix, leaving all the straw gathered to bale for wall construction.

Step 1 – Research

Investigate the different types of earth plaster formulas by surfing the Internet. There are numerous formulas available that can help obtain different finished looks. Choose the formula that suits you best.

The formula below includes clay, sand, flour gluten, cattails and cow manure.

Step 2 – Sift Sand

Sift 15 gallons of sand through 1/8-inch hardware cloth to prepare for a mixture to cover about an 80 square-foot surface.

Step 3 – Spread out Tarps

Spread out several heavy-duty construction tarps and pour the sand upon it.

Step 4 – Add Water to Clay

Place 15 gallons of clay in a mixing container or several five-gallon buckets. Add water until you can put your hand in without leaving a print.

Step 5 – Sift the Clay

Sift 7 gallons of the clay mixture through 1/8-inch hardware cloth directly onto the sand on the cloth. Mix it until well-blended.

Step 6 – Cook Gluten

Using two one-gallon pots, bring water to a boil. Add 3 cups of white flour to each, stirring until it thickens. Add to the clay and sand mixture.

Step 7 – Add Cow Manure

Add a gallon of cow manure to strengthen the mixture. Don’t worry about the smell—it will disappear after it hardens in the mixture.

Step 8 – Add Cattail Fluff

Add the white fibrous substance from inside cattails to the mix.

Step 9 – Mix It All Up

The best method for obtaining an even mix is to get on the tarp with a bunch of friends and stomp and roll until the entire mixture is well blended and ready for use. Wear heavy work boots to ensure that you don't get injured stepping on any fibrous or rock-like particles.