Alkaline surfaces must be recognized if a solvent based paint is to be applied.
Plaster Asbestos sheeting
Definition - having a pH greater than 7 ( an acid has a pH of less than 7 )
Asbestos sheeting, concrete, cement rendering and some plasters, have a chemical nature of alkaline. This will become difficult if a solvent based paint system is being applied because the alkalinity on the surface can attack the paint and take on the properties of a paint stripper, causing a paint defect known as sponifictaion.
( Sponification - a chemical reaction that makes soap and so foams up as a result. )
It is necessary to apply an alkali-resistant primer to prevent sponification, which forms a barrier between the paint and the surface. Acrylic surface coatings are resistant to alkalis, so you would think an alkali resistant primer wouldn't be needed, but they are, however, permeable. ( permeable - allowing things to pass through ) - if the surface becomes damp, nature allows any alkalinity through.
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