Painting Stainless Steel (Again)
I had a problem with adhesion on spun aluminum parts that were being coated with a clear acrylic gloss bake enamel. When we switched to an aluminum oxide sanding medium the problem disappeared.
Q. You pretty well covered T.J.’s adhesion problem in the November Painting Clinic. There is one factor that was overlooked, and that has to do with sanding. I had a problem with adhesion on spun aluminum parts that were being coated with a clear acrylic gloss bake enamel. If I remember correctly, the parts were degreased and then sanded using a silicon carbide paper or cloth. When we switched to an aluminum oxide sanding medium the problem disappeared. S.B.
A. In the November 2008 Painting Clinic question “Painting Stainless Steel,” T. J. was painting stainless using a procedure for painting cold-rolled steel. I recommended changing several things. In the last paragraph I outlined the recommended procedure for painting stainless steel: “...clean the surface to remove oily soils, roughen the surface by sanding or abrasive blasting and apply a vinyl wash primer according to the supplier’s instructions.”
As S.B. points out, there can be problems using blasting or sanding to pretreat metals. For example, embedding of blast media in the metal surface could cause galvanic corrosion and subsequent loss of coating adhesion. In the case of sanding it is also possible that the adhesive binding the media to the paper or cloth backing could contaminate the surface and cause loss of adhesion. Thanks, S.B.
Better adhesion, enhanced corrosion and blister resistance, and reduced coating-part interactions make pretreatment a must.
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