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| tiny little pinholes in my Nitro lacquer finish http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10123&t=43799 |
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| Author: | John Sonksen [ Sun Jul 13, 2014 12:40 am ] |
| Post subject: | tiny little pinholes in my Nitro lacquer finish |
I've just buffed out my latest build and while the finish is overall very nice, it has on the surface the tiniest little pinholes. I used Behlen's nitro lacquer over their vinyl sealer, with some of the first coats being mixed with transtint colorants. The back of the guitar is Sapele and the face is Maple, and the finish is doing the same thing on both sides so I'm reluctant to think it had to do with pore filling. On the Sapele I pore filled with pore-o-pac after doing my sealer coats. The nitro was given two plus weeks to cure before I started my wet sanding and I started with 400 grit, moving up to 1200 before I started with Maguire's ultimate rubbing compound with a foam pad on a right angle grinder/polisher. (still haven't gotten my buffing wheels to do a mezerna setup). I didn't thin the lacquer when I sprayed it except a little in the color coats, and I used lacquer thinner. Does anyone have any experience with this kind of thing happening, or offer any reasons as to why it did or how to avoid it? The pinholes are really small, to the point where I don't think I need to fix it, but I'd like to figure out how to avoid it none the less. The only thing I can think of is maybe I should have thinned the lacquer a bit or used a retarder to give me enough open time for bubbles to escape. I certainly didn't see any indication of bubbles in the finish while I was spraying and only stirred the lacquer before I put it in the gun, I didn't shake it at all. |
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| Author: | Chris Pile [ Sun Jul 13, 2014 5:53 am ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
Sounds like the nitro was drying too fast. Condition known as nitro pop. Suggest using a little retarder to flow it out. |
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| Author: | Stuart Gort [ Sun Jul 13, 2014 9:37 am ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
Ya...retarder and maybe some reducer to spray in on thinner. What happens is that the nitro is skinning over before ALL the solvent gets a chance to leave. The trapped volatile solvents separate into tiny bubbles. If the bubbles are very tiny and there are millions of them, evenly spaced....this is definitely what happened and only using retarder will prevent it. |
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| Author: | Stuart Gort [ Sun Jul 13, 2014 9:41 am ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
Here's my mixing schedule which has worked well in all types of weather. viewtopic.php?f=10101&t=40958&p=538422&hilit=retarder#p538422 |
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| Author: | John Sonksen [ Sun Jul 13, 2014 10:31 am ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
yep, this sounds like what's happening. You know, I've sprayed hundreds of cabinets and thousands of cabinet doors, tables, etc. and have always thinned my lacquer. This is the first time I've ever sprayed it straight out of the can without reducing but I've heard so many people say they do that I figured I'd give it a shot. Looks like I should have stuck with what I know works in this case. I'm trying to remember what the weather was like but it very well could have been during one of our hotter few days a few weeks ago, which I'm sure didn't help. Out of curiosity Stuart, what do you use as a retarder? Typically I try Butyl Acetate first which stays open just a bit longer than L Thinner, but in some cases I've even gone to a tiny bit of Butyl Cellosolve with particularly difficult conditions. My supplier has told me not to exceed 2-3% of Butyl Cell though. I've also used a blend of the two and found it to work. I've only encountered blushing when we haven't been careful enough to bleed the compressor during the most humid days of summer. |
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| Author: | Stuart Gort [ Sun Jul 13, 2014 12:39 pm ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
John...I'm buying the line of Mohawk products...lacquer, reducer, and retarder. I use a filter right before the gun line and have several traps along about a 40' length of pipe on a gradation traveling to the spray room. I've never had a hint of moisture get that far down the line. I played with the ratios for quite a while and found that the recommendations for retarder of Phil at Mohawk were based on using less reducer than I po. I settled at the ratios because I like my eight topcoats to lay down thin. I mix 100 parts reducer and 5 parts retarder. Call that the "additives mix". Then I mix 3 parts lacquer to 1 part "additives mix". This took care of the trapped volatiles and I haven't seen them since. |
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| Author: | B. Howard [ Mon Jul 14, 2014 7:09 am ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
I spray my high solids nitro straight from the can most days. Solvent pop will happen if I put down a wet film in excess of about 4 mills. I add a small amount of retarder/thinner of the appropriate evaporation rate when temps and humidity get high. I never add more than 10% thinner. if you need more than 10 % you are using the wrong speed of thinner. |
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| Author: | John Sonksen [ Mon Jul 14, 2014 8:24 pm ] |
| Post subject: | Re: tiny little pinholes in my Nitro lacquer finish |
I think I tried to build it up too fast. It was a warmer day but not in the 90's or anything. The finish was flashing over quickly and I just kept spraying. I won't make this mistake again, thanks guys. |
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