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I'm painting a mural onto an exterior stucco wall. How can I determine if an already painted wall is oil based or latex?

I'm painting a mural onto an exterior stucco wall. How can I determine if an already painted wall is oil based or latex?
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Posted 2016-01-12T03:01:27+0000  by Davidjoynerart Davidjoynerart
 

There are a couple simple checks for whether a paint is latex or oil: 

A rag soaked in denatured alcohol ( grain alcohol) will readily soften latex paint, but not touch an oil paint. The latex clean-up solvent "Goof Off", which is available at Home Depot, will also immediately attack latex, but have little effect on oil paint.

Another easy test is to simply sand an area of the paint. If the paint dusts up, it is most probably an oil paint. If it does not dust up and tends to clog the sandpaper, it is probably latex.

An educated quess, is that it your wall is probably coated with a latex/acrylic paint, because latex has long been the paint of choice on masonry, stucco being basically a cement product. Latex/acrylic paints have superior elasticity, better bonding, superior color fastness, and the ability to let water vapor pass through the film without causing it to fail. 
Posted 2016-01-12T06:27:34+0000  by ordjen
Once again, Ordjen "Nailed It."

If denatured alcohol simply polishes the surface, it is oil-based.

If denatured alcohol transfers paint color to your rag, it is water-based.

CAUTION:
Outdoor murals are frequently covered by protective clear coats.

The trick is finding the right one.

In the MinWax line, only the Spar Urethane is suitable for exposure to sunlight (UV rays).

However, this and most other oil-based clear coats are not designed to cover water-based paints and stains.

Behr Wet-Look Sealer and Behr Low-Lustre Sealer are both rated to go over oil- and water-based paints and stains and are also rated for exterior application.

 
Posted 2016-01-12T17:06:28+0000  by Pat_HD_ATL
 
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