[Cob] Limewash/Whitewash and other permeable paint options

[Simon Matthews]

Thanks for your reply

On Fri, 2009-03-06 at 20:25 -0500, Henry Raduazo wrote:
> Simon: I did two layers of horse manure and clay on my wall, then a  
> thin layer of lime putty (2 parts sand one part lime) then two coats  
> of lime wash. I sprayed water on the lime layers three times a day  
> with a 2 gallon insecticide sprayer.

I am interested to know why you made the last plaster coat with lime and
sand. Was it to provide a good base for the whitewash?

We are lucky in that one part clay/subsoil from our property with two
parts river sand produces a render that doesn't crack and feels very
solid, rather like a cement render. The one problem with it is that it
is dark chocolate brown which i would think will take many coats of
whitewash to cover. I was thinking of doing a plaster coat purely to
make a light base to put the whitewash on. 

>  You can't rub my lime off. I  
> don't even think you can sand it off, and I have not redone my wall  
> for ten years. It is an interior wall with out much rubbing, but that  
> would not matter.

To date I have done a small test of three coats of whitewash applied one
day apart directly to the mud render making sure to keep the surface
damp. Wiping a finger across this test sample will leave a thin smear of
lime on my finger but the coating remains intact. Is this normal?

>  It has lots of impurities in it so it is not edible grade  
> but it is cheap. Just add water and use, or store in a sealed drywall  
> bucket covered with a layer of water. You should be able to make a  
> bench and sit on the bench with out getting powder on your clothing.  
> If your lime does not harden like, this it is no good.

I noticed that the hardware store had two brands of hydrated lime for
sale. I might try the other brand. I assume that if some of the hydrated
lime is calcium carbonate and not calcium hydroxide as it should be that
the calcium carbonate might not become part of the crystal structure of
the cured whitewash and this might be what is coming off on my finger.

Simon