Stomping around in a mud pit may not seem like the most civilized activity in which a highly evolved hominid can participate. However, if the mud squishing between your toes is an earthen plaster destined to adorn the walls of your home, this pursuit may just turn out to be one of the most enlightened acts of civility you can engage in. Earthen plasters, lime, and gypsum are kinder to the environment than “modern” products such as cement and synthetic stucco—and they provide unrivaled beauty and superior protection.

Earthen plasters

Earthen plasters date back thousands of years. For as long as humans have been building shelters out of mud and grass, they have likely been coating interior and exterior walls with earthen materials to safeguard against wind and weather. Although earthen plasters may seem like an anachronism in a world of sophisticated building materials, they are a highly appropriate choice for homes in many climates, from hot and arid to cold and rainy, provided walls are protected from rain. They provide durable, protective wall finishes far more breathable than modern substitutes.

Suitable for both interior and exterior walls, earthen or mud plasters typically consist of local clay-rich subsoil. (With the exception of desert climates, topsoil contains too much organic matter to be suitable for an earthen plaster.) The subsoil, containing a mixture of clay, silt, and sand, is mixed with water. Straw or some other fiber is stirred into the mix, and then the plaster is applied to walls.

Earthen plasters are applied in two to three coats, depending on the type of wall. Straw bale walls typically require three coats. Adobe, cob, and rammed earth walls provide smoother working surfaces and therefore usually require only two coats. Many mudders apply the earthen plaster by hand, although trowels can also be used. Hand application often results in a better bonding of the plaster to the walls, and it’s an easier technique to master. Earthen plasters dry in a few days to a few weeks, depending on the climate. When finished, they produce a stunning finish that is both warm and inviting.

Pros and cons of earthen plasters

Earthen plasters offer many advantages over other wall finishes, especially cement and synthetic stucco. They are extremely environmentally friendly. Earthen plasters are typically harvested locally—often from the dirt excavated to build the foundation or the basement of a home. They require very little energy to extract and “manufacture.” Costs for making earthen plasters, such as excavating dirt, equipment, and additives, are minimal too. (Dirt must be screened to remove pebbles and debris; straw or some other fiber is often added, and you may need to add sand or clay or additives to improve the plaster mix’s performance and function.)