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Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Paint Peeling from Concrete

Q. In a large condominium complex of four sixteen story buildings with three levels of parking garage in each, spray equipment was used to apply latex eggshell enamel over original 20-year old paint in parking garages. Block walls and concrete ceilings and columns.

Within in 4-5 weeks, after two buildings were done, (6 garage levels) paint began to peel off, taking with it the original paint. That is, the paint peel cosisted of coat of new paint over old paint. Area was power washed prior to painting.

If paint had been applied by brush and roller, instead of spraying, would this have made a difference?

What chemical in new paint would have caused this?

A. Now that I've read a more detailed description of the problem, I would guess that the power washing might be the cause, due to moisture being entrapped in the concrete behind the old paint. When old paint and new paint peel off together, it is generally due to something that is happening at the interface between the concrete and the old paint. Moisture can cause such a problem. Another possibility is that the pressure of the power washer was too high for the old coating system, and possibly the old coating started to pull away from the concrete even before the new paint was applied. Finally, do you actually know how good the adhesion was between the old paint and the concrete (even before the contractor used the power washer). Again, I do not think that spray painting is the cause.

Best wishes,

Ron Joseph

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