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large-area touch-Up

What would be the possibility of touching up a large area and curing with a controlled heat source?

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Q. I have a quick question about touching up of powder paint. What would be the possibility of touching up a large area, let’s say a 12 × 12-inch spot, and curing with a controlled heat source that would concentrate the heat in such a way that it would allow baking of new powder without damaging the outer layer powder surrounding the 12-inch area? H.B.

 

A. Unfortunately, you will not be able to use powder to do an isolated spot of touch-up on a larger surface. When you apply powder over powder you must coat the entire part 100%. The touch-up area will show a very rough and grainy line between the area you coat and the original coat.

It would also be very difficult to apply a heat source selectively to a small area and achieve proper cure, and you may risk discoloration of the original coat.

If you must touch-up an area as large as 12 × 12 inches without rerunning the entire part, you could try a liquid touch-up paint. Powder can be color matched with an acrylic spray. These aerosol spray cans are good for small, cosmetic touch-ups but not too good for larger patches— performance of the acrylic will not be as good as the powder, so it may fade or break down in a relatively short period of time.

You can also use a two-component urethane liquid. This will give you better performance, but it will still be hard to avoid leaving a noticeable parting line. The best thing to do from a performance and appearance standpoint is to somply recoat the entire part. Cycle it back through the system and apply a complete second coat.

If you do recoat the part, be aware that the insulated surface will be harder to cover due to electrical resistance. Use low amperage (<20 µA), increase powder flow slightly, and keep the gun a little further from the target than normal. Be sure to get complete coverage; any missed areas will look grainy and dull. 

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