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| Mysterious cross brace image http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=8393 |
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| Author: | David S. [ Sun Sep 10, 2006 4:14 am ] |
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My first post and my first guitar. I'm having an odd problem.Presently I'm spraying nitrocellulose from a can. My undercoats are dewaxed shellack from a can and a lacquer sand and seal. I've now put on about 4 coats of the nitro. after the first couple of coats I sanded and wiped down the guitar with naphtha.Today I layed down a pretty good coat and upon drying the cross bracing is showing, along with a milky quality to the finish. I believe the the milky quality may be because of the lacquer being too thick, but what is going on with the shadow of the bracing showing through? I was going to add an image but am unsure how to reduce the file. I will add that the top is redwood. Any help on why or how the shadow of the bracing could show through 1/10" of guitar top would be greatly appreciated. |
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| Author: | David Collins [ Sun Sep 10, 2006 4:27 am ] |
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It sounds like the humidity is too high where you are spraying and you are experiencing blushing. Mix in a little butyl cellusolve to your next few coats and spray them a little thinner and lighter than before and it should go away. Butyl cellusolve is often sold as a lacquer retarder, and it slows the drying process to allow moisture to escape as the VOC's evaporate. |
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| Author: | David Collins [ Sun Sep 10, 2006 4:32 am ] |
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Oh sorry, I just reread your post and saw that you are spraying from a can. If you're using nitro, the blushing should still bleed through to the surface and come off with rubbing, buffing or steel wool, but it may take a little while if the humidity is too high. In the case of canned lacquer where you can't control the mixture or content, you just have to adjust your spraying pattern and schedule for the humidity. In dry weather you may be able to spray coats at 20 minute intervals, while in higher humidity you may have to wait as long as 2 hours and spray lighter. If the humidity is too high (above 70-75%) it may be best not to spray at all until the weather cooperates. |
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| Author: | A Peebels [ Sun Sep 10, 2006 8:27 am ] |
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The blushing is probably not seen at the braces because of the extra thickness added by the brace. This would account for the "imprinting". I believe that one of the suppliers sells butyl cellusolve in spray cans as blush ereser. Al |
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| Author: | TRein [ Sun Sep 10, 2006 8:38 am ] |
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Back in the Dark Ages when I was lacquering, I found that simply re-coating the blushed surface erased the blush. If you continue to spray with a can, you might want to wait for drier weather. I never used blush eraser, but I would be hesitant to spray a slow evaporating solvent like cellusolve directly on the lacquer film. It seems like it would be many moons before it totally gassed off. Retarders are meant to be added to the liquid lacquer in small quantities to slow down the evaporation of the solvents. If you mess with retarders, which are very toxic, without proper protection, you are likely to become "retarded" yourself. |
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| Author: | David S. [ Sun Sep 10, 2006 9:58 am ] |
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thanks everyone, i easily sanded it out and recoated with no problems. |
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| Author: | Scott Thompson [ Mon Sep 11, 2006 3:23 am ] |
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By the way, welcome to the forum, David! |
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