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Want to learn the Beautiful art of clay plaster?

Creating gorgeous clay plaster isn't quite as easy as just slapping a bunch of mud on a wall. It's an ancient art and science. If you're serious about earthen plaster work, you might want to have a look at my popular online course.
Take a look at the course

Do You Know Your Plaster?

15/5/2018

7 Comments

 
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/clay plaster (possibly with lime added)
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Earthen plaster uses clay as a binder
Classic clay/earth plaster is a natural wall render usually made from a mixture of clay, straw, and sand. Clay is the binder here. Sometimes, depending on the clay or the climate, folk add lime to this mixture. This doesn’t make it lime plaster though. Lime plaster is something totally different. Clay plaster is a beautiful, malleable and tough natural render. If you want to learn more about it, have a look here.
 
Lime plaster
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Lime plaster is harder and less flexible
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)
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Lime wash works great as a finish for earth buildings
​Lime wash is not a plaster at all. 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. 
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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.
​                                                                              ***
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7 Comments
Cath Coffey
18/5/2018 02:46:55 am

OMG!
Was in the middle of agonising about the amount of money I would have to spend putting lime plaster over my first coat of earth plaster.....you saved me! Phew...Thanks again. I can sleep now.

Reply
Atulya
18/5/2018 01:23:16 pm

Phew! So happy you didn't do that. Your earth plaster may well be enough, but if you want extra protection a lime wash is perfect.

Reply
LS
14/2/2020 11:53:33 am

Hi there,

What would you recommend to cover a cob dome oven with to make it more resistant to rain please?

Reply
Atulya
19/2/2020 12:29:39 pm

Well normally cob will deteriorate if it sees a lot of heavy rain, so best to cover it some how. But several coats of linseed oil will help.

Reply
Rob'O O'Donnell
14/2/2020 02:39:45 pm

I am very intetested in your information.

Reply
Magali.
11/3/2022 02:41:21 am

Thank you for making it so clear! We built cob furniture in our strawbale home. For the dining bench, we are thinking lime plaster as render because it is more rigid, but would you say a clay plaster would be durable with such traffic of people sitting and kicking heals into it?

Also, what did you use to set your beautiful mosaic sculpture into on the last picture?

Reply
Victoria Addington link
26/4/2022 01:43:36 pm

I liked how this post shared that lime plaster is a mixture of lime and sand. My brother wants their property to get plastered. I think it's best to turn to a company that offers plaster supplies services.

Reply



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  • Home
  • Building
    • Earthbag >
      • Rubble Trench Foundations
      • Earthbag in Extreme Weather
      • Earthquakes and earthbag
    • Earth Plaster
    • Using Lime
    • Cob
    • Straw Bale
    • Wattle and Daub
    • Inspiration
    • Off-Grid Living >
      • Off-Grid Prep Course
    • Mud Building Blog
  • Books
    • Dirt Witch
    • Mud Ball
    • Mud Mountain The Book
    • MUD BUILDING PDF PACKAGE
  • About
    • Contact
    • Mud Home Facebook Group
  • COURSES
    • ATULYA's In Person Workshops 2025
    • Perfect Earth Plaster Online Course
    • Lime for Beginners Online Course
    • MUD BUILDING PDF PACKAGE
    • The Off-Grid Roadmap
    • Consultation
  • Blogs
    • Mud Home Turkey
    • Barn Life in Spain
  • My Projects
    • The Earthbag Home in Turkey
    • The Barn in Spain