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Lines in Paint at Door Panel Glue Seams 
Question
Forum Responses
From Gene Wengert, forum technical advisor: A joint can appear when there are moisture issues, especially if the panels were planed or polished too soon or when there was a moisture gradient. In almost all cases, the door can be re-sanded or polished and there will be no problems (assuming that the glue joints were properly made). From Gene Wengert, forum technical advisor: There is another possible cause and that is when there is an oven used to cure the finish. The heat can melt the adhesive, creating a void that will show up after the finish is dry, especially with glossy finishes. It is also possible for the finish to dissolve a bit of the glue. From contributor B: Your finish in going on too wet, and the solvent is penetrating into the glue, causing the glue to swell, in turn creating the ridge between the panels. This is hard to avoid when using nitrocellulose lacquer. Once it starts to swell, it’s harder to get to stop. Really the joint isn’t as tight as it could be and that’s when you see that the most. You need to mist on primer over that area until it is completely covered. Only mist the crack, do not get it wet (yes there will be orange peel and will require extra sanding). You cannot get that area wet until you have a barrier over it, and even then if it stays wet for more than a minute it can resurface. If you’re using nitrocellulose lacquer, you cannot allow the joint to stay wet for more than a minute or two. Once it’s primed, the first topcoat needs to be thinned super thin and sprayed in the thinnest possible coat you can spray (high pressure, low volume). Once you get a small coat on, you can gradually increase the solids until you get good coverage, but the piece will need to be sprayed in super-thin coats, every coat. With nitrocellulose lacquer, each coat re-melts all previous coats. If wet long enough, and the moisture can leach back into the glue on your final coats, re-raising it, even though you eliminated the flaw in the priming stage. This is tough to do if you live in a hot humid area, because super thinned out coats full of fast dry lacquer thinner can blush easily.
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