![]() You could import hydraulic lime from Europe, where the tradition of lime plaster has not been broken, but at a high cost financially and environmentally. It still requires knowledge and skill, but it sets faster and more consistently with less babying. It is not an easy process but it results in a water-resistant, durable, vapor-permeable finish. On larger-scale projects, like the exterior of a strawbale home in a climate that gets sideways monsoon rains, we will make our own Type S lime plaster, don our gloves and safety glass, make the mix ourselves, apply the plaster skillfully before it begins to set, and then tend to it patiently until it has cured. Although it is possible to make a good lime plaster from locally available Type S lime, it requires knowledge, skill, and a fair bit of babysitting to succeed. Then it became difficult to source lime of high enough quality to produce consistently good lime plaster. Lime plaster used to be very common in the US but was replaced by drywall and gypsum-based plasters in the last century. It is harder and more impact-resistant than clay but that makes it more difficult to repair. (If you do it wrong, it turns to useless dust on the wall.) Done right, it will not erode. If you do it right, lime plaster goes through a chemical change as it cures that effectively turns it back into limestone on the wall. ![]() Lime plaster is less vapor-permeable than clay plaster but is more vapor-permeable than cement (lime plaster is 9 perms per 2″ where straight cement plaster is less than 1 perm per 2″). Lime plaster has a much higher carbon footprint than clay plaster, it is only slightly lower than cement plaster. Sometimes a project or situation requires a plaster that can fulfill different duties. Clay plaster is easy to repair but many people do not want to have to care for their walls. Outside corners in high-traffic areas often suffer chips and dings. It is also not as hard or impact-resistant as some finishes. Magic.Ĭlay plaster has many benefits, but it does have some real limitations. You can write on clay plaster with a Sharpie marker and erase it with a damp sponge. Clay plaster has hygric mass and can help balance indoor humidity. It doesn’t bounce sound or cause echoes as much as harder finishes. Clay plaster is also anti-static which helps it repel dirt and dust. This makes it ideal for any building system where you do not want trapped moisture - which should be the goal for every building system but is often ignored in conventional construction. ![]() It draws you towards it and makes you want to touch it: I can’t explain why but it’s true.Ĭlay plaster has some magical qualities: it is one of the most vapor-permeable finishes, coming in at 11 perms per 2″ of plaster. In terms of beauty and attractiveness, clay plaster is hard to top. It is minimally processed, needs no additives, and can be sourced locally. In terms of minimizing environmental impact and carbon footprint, you cannot beat clay plaster. I love clay plaster, it has so much going for it. ![]() When I consider what plaster to use, I always think of clay plaster first. ![]()
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