Distinguishing earthen plaster, lime plaster and lime wash
Earthen or clay plaster, lime plaster, and lime wash: these are three things people often confuse. And it pays to be able to distinguish them, because each behaves differently on a wall. Here’s a quick clarification.
Earthen plaster (possibly with lime added)
Classic clay/earth plaster is a natural wall render usually made from a mixture of clay, straw, and sand. Sometimes, depending on the clay and climate, folk add lime to this mixture. This doesn’t make it lime plaster though. That is something totally different. Clay plaster is a flexible, breathable render. If you want to learn more about making it, sign up for my free earth plaster PDF and email course.
Lime plaster is simply lime mixed with sand. Sometimes people will add a pozzolan like ash to create a more cement-like result. But that’s basically it. Like earthen plasters, lime plaster breathes and can be used as a natural render. It also has other benefits; lime is both a fungicide and an insecticide. BUT, beware of using lime plaster to cover cob or earthen buildings, as it may crack.
Why might lime plaster crack? If your walls are mud (adobe, cob, earthbag) when the rains of winter begin, the clay in your wall will expand as it gets wet. In summer that same clay will shrink back as it dries. The trouble is the lime plaster doesn't expand or shrink alongside. Unlike earthen plasters, lime plaster is more cementitious and rigid, so what tends to happen (especially in climates with monsoons or heavy rains followed by dry weather) is that the lime plaster eventually cracks and pulls away from the wall.
Lime wash (using lime as a whitewash or paint)
Lime wash is not a plaster. It’s a final paint-like finish made from lime, water and a binder such as casein (more on how to make it here). Lime wash can be used much like paint on cob or earthen buildings, and this breathable finish will protect the plaster underneath very successfully. Unlike lime plaster, lime wash won’t crack (or at least only slightly) because it is only a thin lime layer, as opposed to a render. When your lime wash begins to see wear over time it’s very easy to repair, simply by painting more lime wash into the cracks.
This was my mud home in Turkey. The earth plaster is coated in a lime wash (except the sills and sculptures, because I wanted them to stand out).
I hope that’s unmuddied the waters a little.
If you enjoy from these posts and would like to keep The Mud Home running, do consider making a pledge on Patreon. All contributions, no matter the amount, are deeply valued. When you become a Mud Patron, you can join my private news feed and become part of our thriving mud club. If you need help or motivation with a project and want access to an exclusive community of builders and experts, I strongly recommend joining our private FB group. Members are finding it very inspiring and instructive.
Many thanks to the Mud Sustainers supporting this site!
Do you find The Mud Home valuable? Please consider supporting the blog on Patreon. For as little as $2 a month (not even a coffee where I'm from), you can join the club.
BENEFITS FOR PATRONS INCLUDE:
Email priority, private Facebook group, review copies of my books, sneak previews of courses and books, Q and As, priority for courses and more.
Atulya K Bingham
“Entranced! Be inspired by one who’s lived and breathed dirt.”
Kim Sui, Get Rugged
"Beautifully written and inspiring." The Owner Builder Magazine
If you want the step by step guide of how I built my house, sign up for the PDF.