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| Bumps in finish http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50458 |
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| Author: | dofthesea [ Mon Mar 26, 2018 2:40 pm ] |
| Post subject: | Bumps in finish |
Anyone know what this might be? Im spraying lacquer and am wondering if its moisture? Ive sanding them down 2 times and resprayed and they keep popping up. |
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| Author: | truckjohn [ Mon Mar 26, 2018 2:56 pm ] |
| Post subject: | Re: Bumps in finish |
Do they keep popping up in exactly the same spots? If you sand one down very carefully - look with a good light shining across the finish and see if you see a fine little whisp of hair/fuzz sticking up.. If so - it's dust/lint/hairs.... Groan... Let's just say that in my context - "The hair of the dog" refers to special inclusions in my finishes, not something fun the night before. 
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| Author: | wbergman [ Mon Mar 26, 2018 3:10 pm ] |
| Post subject: | Re: Bumps in finish |
I also noticed that dandruff would get into lacquer finish. In my example, the final leveling and buff out left them not visible. |
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| Author: | Barry Daniels [ Mon Mar 26, 2018 3:42 pm ] |
| Post subject: | Re: Bumps in finish |
That looks like "solvent pop". This is caused by the finish curing before the solvent has had a chance to escape. A bit of retarder in the lacquer will fix this. |
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| Author: | Woodie G [ Mon Mar 26, 2018 3:45 pm ] |
| Post subject: | Re: Bumps in finish |
If viewed with a 10x hand magnifier, do they look like volcanoes or mountains? Something that looks like a raised ring with a depression in the center might be an open pore or (if a bit larger that what is evident in your shot) a fisheye, while a mountain-like hump is probably dust or other debris. You might consider scraping level before shooting the next coat in either case. |
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| Author: | dofthesea [ Mon Mar 26, 2018 9:55 pm ] |
| Post subject: | Re: Bumps in finish |
I scraped and sanded them down then they reappeared when I shot a new coat...... grrrrrr. Ok I think I'll try the retarder. I sprayed out about 40 other cabinet doors with out any problems and the raised bumps was random fyi |
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| Author: | Barry Daniels [ Mon Mar 26, 2018 10:16 pm ] |
| Post subject: | Re: Bumps in finish |
Solvent popping usually occurs during hot weather when the lacquer cures quicker. Sherwin Williams sells a special lacquer thinner with some retarder added to handle the summer season here in Houston. Or you can buy a can of retarder and add it yourself. |
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| Author: | Woodie G [ Tue Mar 27, 2018 8:15 pm ] |
| Post subject: | Re: Bumps in finish |
Did you shoot in the sun? Temp? RH? All 40 doors received the same sand and fill? |
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| Author: | B. Howard [ Thu Mar 29, 2018 3:44 am ] |
| Post subject: | Re: Bumps in finish |
Solvent pop. Here is a handy problem solving chart I made for spray finishes. https://howardguitars.blogspot.com/2015 ... rt_18.html |
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| Author: | dofthesea [ Fri Mar 30, 2018 9:44 pm ] |
| Post subject: | Re: Bumps in finish |
Thanks for the info fellas mucho gracious |
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| Author: | dofthesea [ Fri Mar 30, 2018 9:45 pm ] |
| Post subject: | Re: Bumps in finish |
I was shooting in the shade. it was a bit on the cold side like maybe 60-65ish. |
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| Author: | Clay S. [ Fri Mar 30, 2018 11:05 pm ] |
| Post subject: | Re: Bumps in finish |
I've had that happen when I've sprayed a finish in a cold environment and taken it to dry in a warm environment (to avoid blushing). I blame it on the piece losing moisture trying to regain equilibrium with the relative humidity in the new (dryer) environment. The moisture coming out of the wood's pores causing the air bubbles as the finish cures. |
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