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September 14 - September 19, 2010

What kind of surface preparation prior to coating will be effective and at the same time economical for the aluminum window frames on a large commercial office building? The aluminum was coated originally with a baked-on fluoropolymer which has lost most of its gloss. Maintenance recoating will be with an air-dry fluoropolymer.

Selected Answers

From Joseph Schinner of Akzo Nobel Coatings Inc. on September 16, 2010:
This will be labor-intensive, so after the cost of the coating, time controls the economics. Anything less than a fluoropolymer will be short-lived. The question doesn't identify what the original coating binder is, but if it was a fluoropolymer and was shorter-lived than expected, perhaps a different fluoropoymer will last longer- even if a different starting gloss will have to be chosen. Frequently, a top to bottom soapy water wash with thorough rinse and complete dry is adequate to get rid of surface dirt contaminants and let the refurbishing coat adhere. If this proves inadequate, then a "scotchbrite" scuffing/wipe will be necessary. It is imperative to conduct a trial with a test patch, maybe at both north- and south-facing spots, as well as lower window and high window matrix if the building is tall or there is uneven distribution of "dirt" exposure from traffic, etc.

From Adam Backhaut of Volkswagen Group of America on September 14, 2010:
If the current coating is showing good adhesion properties, I would not worry about removing it. I recommend scuffing the surface with 400-600 grit abrasion, cleaning with a good pre-clean solvent, and then top coating with an exterior polyurethane system. If the current coating is failing, I would recommend removing it and then coating the aluminum with a DTM epoxy primer prior to top coating with the polyurethane. With some DTM polyurethanes, you may skip the primer, but I always recommend using primer for better adhesion and durability.

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Tagged categories: Fluoropolymer; Surface preparation

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