Recoating a Permanent Structure
Q. I am a faux painter and have been unable to find a solution to a possibly unique problem with a powder coated aluminum outside railing. A square-tube, aluminum railing was powdered coated when new (less than three years ago), then permanently installed in an outside setting in a mountain location. Over the winter, the tubing filled with water and froze, causing expansion in the aluminum, which resulted in the powder-coated finish peeling in several places. Unable to contact the one who originally applied the coat, the owner has called several painters and me (a faux painter) to try to repaint the bare aluminum patches with a similar finish. No one will tackle the project. I have done some research on your web site, but cannot find a solution to this problem. Keeping in mind that the railing is not removable and must be painted in place, what can be applied that will match the color and texture of a powder coat finish? Is there a way to apply powder coat again while the railing is in place? If the bare spots are painted with something like Krylon, can that be feathered into the existing finish or be safely applied over the existing finish? I am sure that even if the aluminum is primed, the repair will not be as durable, and there will be other potential problems. However, there must be some way to fix this! Your reply is appreciated. J.B.
A. How interesting…a faux painter….Hmmn. I have been accused of being a faux consultant, so I sympathize with your predicament. Of course, I am just kidding. No cards and letters please.
Let me first explain the causation of the powder coating failure. The coating did not fracture by the aluminum tube freezing or expansion either. Powder coatings are very flexible materials and can often take a zero T-bend without fracture. Powder coated parts can even be deep drawn after powder coating (up to six inches and sometimes more). What happened was the powder coating was applied to a poorly cleaned and pretreated surface. The powder may also have not been fully cured. Either way, moisture penetrated the coating, combined with salts and contaminants on the substrate and created a corrosion site that eventually lifted the coating by osmotic pressure. This is a common problem when the process has not been performed properly. It is simply called adhesion loss (or blisters) caused by corrosion failure of the coating.
This failure means that spot fixing the powder coating can be problematic since the adjacent areas will most probably fail, as well. The only bulletproof way of fixing this problem is to completely strip all the powder coating from the part before re-coating the railing. Since the railing is “permanently” installed, this means stripping the powder by grit blasting or sanding. Then I recommend that the surface be wiped clean with a tack rag, primed and top-coated using a two-part polyurethane liquid paint.
Now you see why the other contractors wanted no part of this repair. If you can’t do this repair procedure exactly like I described, or are unfamiliar with two-component liquid paints, then there is only one thing you should do: Run away as fast as your little faux feet can take you. That may sound condescending, but it is the best advice that anyone can give you.
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