Finish TradesQuestion 218 of 700
New portland-cement stucco or fresh concrete is highly alkaline. Applying an ordinary oil-based paint too soon can cause which specific failure?
a.Saponification, where the alkali attacks the oil binder and the paint softens or lifts
b.Excessive gloss and hardness of the film
c.Faster and stronger adhesion than on aged masonry
d.Permanent color darkening with no loss of adhesion
Explanation
Fresh cementitious surfaces are strongly alkaline; the alkali reacts with the oil in oil-based paint (saponification), softening the film and causing peeling. The remedy is to let masonry cure (commonly about 28 days) or use an alkali-resistant primer. Alkali does not increase gloss, improve adhesion, or merely darken color.
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