Originally posted by Alex Sumerall at This Cob House.
Natural plasters and finishes are a great alternative to the conventional products available out there.
The ones that are just riddled with toxic chemicals!
Most people don’t even realize the negative effects that these products have on their health.
Indoor air pollution and toxic off gassing is a whole subject in itself though.
So I just want to give you some earthen plaster recipes today to get you thinking.
Natural plasters and finishes can be applied to cob walls or even to drywall board!
The majority of natural plasters and finishes are made from a combination of these simple ingredients:
Clay, sand, straw, lime, kaolin clay, wheat paste, pigments, and water.
So, here’s a basic recipe for earthen plaster that you can try out:
- 1 part clay-rich soil
- 2 parts sand
- 1/4 part chopped straw
Soak the soil in water for a few days to soften it up.
This will also give it more plasticity.
After soaking, put some of the soil in a bucket with water and mix it with a heavy-duty drill.
Attach a paint mixing drill bit.
Then sift it through a window screen until its like chocolate pudding consistency.
Also sift your sand through a window screen. You want to remove all large pebbles and debris.
Chop your straw up finely and sift it through a ¼” wire mesh.
You can put some straw into a trash bin and stick a weed eater inside to chop it finely.
When all of your materials are ready, put them all together and mix.
I recommend mixing with the drill again for small batches.
This earthen plaster will take on the color of the earth and sand.
If you want a white wall or colored wall, try this recipe on top of it.
First, you will need to make some wheat paste.
Wheat Paste Formula:
- 4 parts boiling water
- 2 parts cold water
- 1 part flour (any kind of flour)
Mix the cold water and flour together with a whisk.
Then pour slowly into boiling water and whisk it all together as you go.
Now for the plaster recipe:
- 1 part sand
- 1 part kaolin clay (you may need to add a bit more than the sand)
- 10-25% wheat paste (you will have to experiment with your unique mix for best results)
- Water (amount varies)
This plaster will give you a nice white finish.
You can also add pigments to this mix.
You need to mix your pigments with a little bit of water before including them in your plaster though.
Dissolving the pigment in water first will make sure that there are no chunks in your mixture and that the pigment gets evenly dispersed throughout.
Your finish will dry twice as light as the original pigment by itself.
So don’t base the final color by your wet plaster’s appearance.