Durable Coatings for Aluminum

Question:

I’m bidding on a job requiring powder coating aluminum windows (the interior side) on site in an apartment building. That does not seem to be possible re: heat curing. So what would be the best finish for repainting, preferably by spray painting? I want something extremely durable and available in a wide range of colors and finishes. It’s a very high end job. Thanks. J.D.

Answer:

Applying powder coating to aluminum window frames, on site, would be a difficult if not impossible task. Applying a liquid coating by spraying would also be difficult, but you already know that. The following steps can be used as a guide.

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First, great care must be taken in the pretreatment step. If they are anodized, which incidentally is an excellent paint base, they must be cleaned to remove oily soils. If the apartments are occupied, the frames can be wiped using aqueous cleaners. If unoccupied, the frames can be solvent wiped and the solvent vapors allowed to dissipate. Some people are very sensitive to solvent vapors. If they are already painted or powder coated, either solvent wiping or aqueous cleaner wiping as mentioned earlier can be used. Compatibility of the solvents and cleaners with the existing coating is an important issue.

Second, a number of liquid coatings are durable enough to replace or recoat powder coating. Since heat cannot be applied, I suggest you consider room temperature curing two-component materials. Polyesters, epoxies and polyurethanes immediately come to mind. Epoxy polyamide coatings have excellent adhesion but poor fade-resistance and should be ruled out. This leaves you with the choice between two-component polyurethanes and polyesters. Either choice is durable and available in a wide range of colors and glosses.