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| Lacquer problem https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=18508 |
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| Author: | jsimpson [ Sat Aug 23, 2008 3:48 pm ] |
| Post subject: | Lacquer problem |
I sprayed two base coats on this guitar a couple days ago, all went fine. Yesterday I sprayed two more in high humidity and this is the result. You can see every brace and support through all around the guitar, not just on the top! Presuming it's trapped moisture, obviously. I've been advised by my buddy Bob Long to wait a couple weeks to let it clear up. Is there some way to accelerate that process? Thanks! |
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| Author: | MacD [ Sat Aug 23, 2008 6:45 pm ] |
| Post subject: | Re: Lacquer problem |
If it's nitro, you can re-flow the lacquer with some retarder or proprietory moisture and bloom remover then let it dry out slowly - do it in sections and keep the area you've sprayed as flat as possible until it's dry, otherwise it might run or sag. For other lacquers I'm not sure - you might have to sand it out. Cheers, Bri |
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| Author: | Allen McFarlen [ Sun Aug 24, 2008 4:11 am ] |
| Post subject: | Re: Lacquer problem |
It's blush, or bloom, caused by moisture trapped in the finish. Don't worry, easy fix, but NEVER try to rush it. It might disappear on it's own, though often not. After a week or two at lower humidity levels, the moisture that is trapped will have been released as well as all the solvents that need to get out before you buff anyway. If you still see the blushing but it's very faint, you may be able to sand back and buff as usual. If not, then sand back a little and spray again a few very thin coats ( 50/50 cut or even thinner ) with better conditions, or to be sure, add some retarder to your lacquer. This will keep the surface open and allow the moisture to get out before the top skins over and gets trapped in the finish. It is possible to spray with straight retarder, but this is really risky for an untrained spray painter. The potential for disaster it too high to recommend. I've been a spray painter for 30 years and I wouldn't try to do this as my first choice. I always add at least 10% retarder to the mix, no matter what the conditions. Helps to melt in overspray. Improves flow out, and eliminates blushing. Also you end up putting on thinner coats, because it flows so much better. |
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| Author: | jsimpson [ Sun Aug 24, 2008 12:12 pm ] |
| Post subject: | Re: Lacquer problem |
ToddStock wrote: I'm going to take a wild guess - the guitar was in an air conditioned space before you sprayed, and was returned to that space as soon as each coat went on, right? Hi Todd - Actually no, the guitar was in my basement shop with no AC going..and at 54% RH. Took it outside and sprayed, let it hang outside for an hour, hoping the blush might wick out. |
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| Author: | jsimpson [ Sun Aug 24, 2008 12:15 pm ] |
| Post subject: | Re: Lacquer problem |
amcfarlen wrote: It's blush, or bloom, caused by moisture trapped in the finish. Don't worry, easy fix, but NEVER try to rush it. It might disappear on it's own, though often not. After a week or two at lower humidity levels, the moisture that is trapped will have been released .......you may be able to sand back and buff as usual. If not, then sand back a little and spray again a few very thin coats ( 50/50 cut or even thinner ) with better conditions, or to be sure, add some retarder to your lacquer.... Excellent, thanks Allen! I'll give it some time and proceed as you suggested. Will be ordering some retarder for next time, for sure! Jon |
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| Author: | Mike_P [ Sun Aug 24, 2008 12:45 pm ] |
| Post subject: | Re: Lacquer problem |
make very sure to read the ratio instructions for retarder and do NOT use too much...the more used the longer the curing time, I've found you usually need just a tad to do the job |
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| Author: | Howard Klepper [ Sun Aug 24, 2008 1:04 pm ] |
| Post subject: | Re: Lacquer problem |
I try to stay away from retarder (butyl cellosolve). It can soften the finish for a looong time. I would first try shooting a wet coat under better conditions (warmer, less humid). |
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| Author: | Allen McFarlen [ Mon Aug 25, 2008 4:06 am ] |
| Post subject: | Re: Lacquer problem |
You guys must be calling retarder something different to what I call it. My mistake if I put you on a wrong path. I will clarify this by calling it Ultra Slow Thinner. Does not affect film hardness at all, just how long the surface stays open. Most people don't realize this, even very experience spray painters get this wrong all the time, but it doesn't make a lick of difference on how long it takes for a finish to cure by changing the thinner between fast and slow. Remember, I said cure. The thinner is only added to the paint as a means of reducing viscosity in order to allow it to be sprayed. The speed of the solvent is chosen by the applicator to suit the spraying conditions, equipment used, and size of job. Using fast thinners will not make it cure faster. Only skin the surface off, making it appear that it has dried quicker. And it's important to remember that drying is not curing. In fact the opposite is far more likely. When the surface skins off it makes it more difficult for the solvents trapped underneath to gas off. All solvents have to gas off before the paint can begin to cure. You will never get a top notch finish if you try to buff out a finish that has not fully cured. It might look good for a week or so, but will fall back as more solvents evaporate and the finish tightens up as it cures. This is a very common problem with many people trying to learn how to get a glassy surface that lasts. The most effective way to get the finish to fully gas off it to place in a well ventilated place with a breeze passing over the painted surface. This will clear the solvent gases that have saturated the air that envelope the painted object and make room for more solvent to gas off. It's not good enough to just let it hang in a stagnant room and waiting a week. In those conditions it will take much longer. This brings me back to your question about the blushing. Water vapor is mixed in with the paint as you spray. It can come from the air stream, ie. your compressor, or the environment, or both. When humidity goes up, more water vapor is mixed in with the paint and gets trapped in the paint film. If the paint film is too thick, or the surface skins off too quickly, it gets trapped and makes the paint blush. Thinner coats by cutting the paint with more solvent, and / or using slower solvent will cure this. Remember that if you will need to apply one or two more coats to your spray schedule if your cut the paint more than normal to achieve the same film build. |
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| Author: | Mike_P [ Mon Aug 25, 2008 6:06 pm ] |
| Post subject: | Re: Lacquer problem |
retarder is a specific chemical mix which retards the curing of finishes....fast, medium, and slow thinners are NOT related in any way... http://www.mlcampbell.com/secured/pishe ... -04-03.pdf I've made the mistake of pushing the envelope with use of retarder and when I delivered some table tops for a lounge one of them ended up with impressions (luckily it didn't stick) of the blanket I had it wrapped in for shipment...the tops had 3 weeks to cure and I was sure (yeah, first mistake thinking, second mistake acting upon said thought!) they were OK to deliver... |
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