Q. I am the foreman in charge of the paint line at my plant. We have been using lacquer thinner to clean aluminum parts before painting. Is this a good practice, and if not, what would be a good low cost replacement? The lacquer thinner is the only pre-primer treatment used. We paint the parts with epoxy paints over a zinc chromate primer. On humid days, the primer turns a chalky color and won’t adhere well to the metal. Can anything be done to correct this? M.J.
A. It is important to remember that aluminum surfaces must be properly pretreated before painting for maximum adhesion. On the other hand, if your aluminum parts are already pretreated and your only concern is removing oily soils, degreasing is a good thing.
Using lacquer thinner to degrease them is a bad thing. Although lacquer thinner may remove oily soils, using it for solvent cleaning is not a good method because it evaporates too quickly. It is also dangerous due to its low flash point. Mineral spirits is a better choice for degreasing and is safer to use. Furthermore, solvent cleaning is not the best pre-paint treatment for bare aluminum. There are a number of commercially available pretreatments for aluminum. I suggest you contact suppliers of these materials.
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As far as the primer turning a chalky color and losing adhesion on humid days, you have two choices. Either change primers or dehumidify your painting area.