Another Source of Dirt in the Paint Film
An imbalance of the chemicals in the power washer could be the root of a reader's problems with dirt in the paint finish.
Q. The question from M.H. in the September issue regarding dirt in the paint film rang a bell. I ran into a similar situation at a large fixture manufacturer in Massachusetts. His white gloss paint finish was loaded with small particles.
After filtering gallons of paint, we still could not get rid of the particles. When we looked for another source of the problem, however, we discovered that the particles were on the parts when they came out of his pretreatment washer. So the paint was not the problem; an imbalance of the chemicals in his power washer was. This imbalance caused larger-than-normal crystals of phosphate material to form on the substrate, giving the appearance of particles in the paint film. I suggest M.H. also consider this as a possible cause of his problem.—S.B.
A. Thank you for writing to Painting Clinic, S.B. Since pretreatment washers are supposed to rinse off particulates in the final rinse, I wouldn’t have expected that to be the source of the problem. But your experience indicates that M.H.’s contaminants could very well be larger-than-normal crystals of phosphate material produced by an out of balance pretreatment solution in his power washer.
Better adhesion, enhanced corrosion and blister resistance, and reduced coating-part interactions make pretreatment a must.
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