Blackdog Posted August 16, 2012 Report Share Posted August 16, 2012 Hi people. I'm still a bit of a beginner with these finishing issues and I'm having a problem with my clear coats. I'm spraying a nitro type lacquer with a HVLP conversion gun, and the problem is that in some areas (possibly where the lacquer accumulated a bit thicker, like headstock face edges and such) I get a kind of prearlescent patches that only show up when the light hits them at the right angle. I sanded the clear back with 400 dry (I had to do it to level the finish a bit anyway), and resprayed a single rather wet coat yesterday, and when I checked this morning I had the problem again. In different places, so it's not that I didn't get rid of it when I sanded, it appeared again. It's not the first time I use this material and equipment (I have finished two guitars prior to the current ones), and this is the first time I have this issue. I was having a bit high humidity in the shop (70%), could it be that ? Maybe I should try laying down less wet coats ? Could this be the effect of water trapped in the air line ? Any ideas ? Thanks a lot for your help. Quote Link to comment Share on other sites More sharing options...
Ripthorn Posted August 16, 2012 Report Share Posted August 16, 2012 I certainly sounds like a moisture problem. Do you have a separator or dessicant inline with your air supply? I would also try to wait for lower shop humidity if at all possible. Quote Link to comment Share on other sites More sharing options...
Blackdog Posted August 16, 2012 Author Report Share Posted August 16, 2012 I certainly sounds like a moisture problem. Do you have a separator or dessicant inline with your air supply? I would also try to wait for lower shop humidity if at all possible. Thanks for the reply. I do have a water filter/trap in line with the regulated air supply I use for the gun. But truth be told, I have never checked it back since I installed the whole thing almost a year ago. It's the first thing I'll check when I get home this evening (I'm at the office now ;-)). I have been googling a bit after I posted and the iridiscent issue (called blooming ?) could be caused by insufficient drying of oil based pore fillers. But for these guitars I have used water-based fillers, and the problem appeared after a number of coats anyway. Right after sanding I cleaned the surfaces with naphtha, could it be that ? I dusted the guitars with compressed air after the naphtha, so it should have been perfectly dry... Quote Link to comment Share on other sites More sharing options...
bob123 Posted August 16, 2012 Report Share Posted August 16, 2012 (edited) edit: Nvm, I think you have a good idea what you're doing does it not go away when you do your finish sanding? Edited August 16, 2012 by bob123 Quote Link to comment Share on other sites More sharing options...
ScottR Posted August 16, 2012 Report Share Posted August 16, 2012 BD, the times I've seen that have always been high humidity days. It did seem worse in the areas with the heaviest coats. It was my impression it was the humidity in the ambient air as opposed to the line air that was causing the problem....but that was just the impression I got. Sorry this is not an answer, but it is a confirmation of similar results in similar conditions. SR Quote Link to comment Share on other sites More sharing options...
Blackdog Posted August 16, 2012 Author Report Share Posted August 16, 2012 BD, the times I've seen that have always been high humidity days. It did seem worse in the areas with the heaviest coats. It was my impression it was the humidity in the ambient air as opposed to the line air that was causing the problem....but that was just the impression I got. Sorry this is not an answer, but it is a confirmation of similar results in similar conditions. SR Hi Scott ! May not be an answer but sure it's reassuring. Today I sanded the finish again. Good thing is that I have almost gotten rid of all the pore filling imperfections already. I decided to build up the lacquer a bit slower, so I sprayed two much lighter coats to both guitars, some 15 mins apart, and will let them rest for a day. It seems to have worked fine so far, the problem seems directly related to the thickness of the coat (and the humidity?). I will repeat the process a couple more times and see how it goes. I intend to keep the final finish as thin as possible anyway. Today I had a bit less humidity too, around 63%, this should also help. Quote Link to comment Share on other sites More sharing options...
demonx Posted August 16, 2012 Report Share Posted August 16, 2012 It'll be happening because you're spraying too thick (as it seems you've already worked out) Humidity etcetc as already discussed will be contributing to it and the fact you sprayed too thick just means that there's all these "wrong" things thrown into one basket, so something is bound to go wrong. Empty your line filters every time you spray. The air valve on your compressor too. Open it till no water comes out. Quote Link to comment Share on other sites More sharing options...
Blackdog Posted August 19, 2012 Author Report Share Posted August 19, 2012 It'll be happening because you're spraying too thick (as it seems you've already worked out) Humidity etcetc as already discussed will be contributing to it and the fact you sprayed too thick just means that there's all these "wrong" things thrown into one basket, so something is bound to go wrong. Empty your line filters every time you spray. The air valve on your compressor too. Open it till no water comes out. Thanks guys. It was not a problem with water in the line. I must have been the high ambient humidity together with the very thick coats. I have been building up the clear with much thinner coats and everything is coming along nicely. Thanks again for the help. Quote Link to comment Share on other sites More sharing options...
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