[Cob] Limewash/Whitewash and other permeable paint options

[Shannon Dealy]

On Sat, 7 Mar 2009, Simon Matthews wrote:

[snip]
> 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?
[snip]

For lime, dry does not equal "cured", and one day is not enough time for 
it to set regardless.  For lime to set requires that it absorb carbon 
dioxide from the atmosphere and this is a slow process, though I am not 
sure how long it would take to pass your "wipe a finger across it" test, I 
would expect at least weeks rather than days, and even then it would not 
be a full cure since the process is non-linear, some carbon dioxide is 
initially absorbed quickly, but the process continues progressively more 
slowly and the tiny bits in the surface which have not cured may continue 
to end up on your finger.

FWIW

Shannon C. Dealy      |               DeaTech Research Inc.
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