Bubbles in lacquer on inside corners

Alan Bienlein

Member
Messages
2,044
We have been having some problems lately with the finish bubbling on the inside corners of guitars that are being finished with lacquer. It happens either at a neck joint or at the bridge on a steel string guitar. We are at a loss as we have tried thinning the lacquer more and we also have tried retarder thinking that might help. Here are a few pictures so you can see what I'm talking about.

The guitars are sealed with de-waxed shellac from flakes mixed with everclear and the lacquer is instrument lacquer from Cardinal.

The first is of a semi hollow guitar where the neck joins to the body.
2016-12-28 14.42.42.jpg2016-12-28 14.42.49.jpg2016-12-28 16.04.27.jpg

This is a steel string and the bubbling is happening on the neck side of the bridge.
2016-12-28 15.42.48.jpg2016-12-28 15.43.07.jpg2016-12-28 15.43.15.jpg2016-12-28 15.44.17.jpg

Any help would be appreciated.
 

Mark E Smith

Member
Messages
190
Location
Arkansas
Just a guess but could it be the glue your using reacting with the lacquer, seems to be the only place your having that problem. Have you changed glues recently. Do a quick test of a joint with scraps using a different glue and the same glue to see if the lacquer does the same thing to both. You can also do a google search of the chemicals used in the glue and lacquer to see if they are compatible..
 

Alan Bienlein

Member
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2,044
The glue we use is 315 # strength hot hide glue. It's all we use plus everything is sealed with dewaxed shellac made from fresh flakes and ever clear.
 

Alan Bienlein

Member
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2,044
The main reason we don't suspect the hide glue is that the whole guitar is assembled with it. As to the sanding residue I will have to check to see how well it's cleaned after sanding between coats.
 
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6,324
Location
Outside the beltway
Like others I say and very small opening between the layer with opening in the glue join. We dealt with that by making sure all glue ups had 100% push out. going excessive in this case is a good thing.
 

Darren Wright

Administrator
Staff member
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17,033
Location
Kansas City, Missouri
The other thing that comes to mind, was if there was something used to dust down the wood prior to lacquering that may have seeped into the cracks and not yet evaporated out?
 

Alan Bienlein

Member
Messages
2,044
When we glue the necks in there is squeeze out that is wiped away in such a way that it leaves a fillet in the corner. That will gradually get sucked into the wood so about every ten minutes the joint is checked and more glue added to the inside corner as needed to maintain that fillet. We have even went as far as trying to seal the corners with fit and finish ca from GluBoost.

I'm starting to think that too much finish is being applied in the corner with not enough dry time between re-coats.

I will discuss all of these recommendations with him when after we get back to it in the new year.
 

Alan Bienlein

Member
Messages
2,044
Today he gave the gun a good cleaning and so far problem has went away. Looks like it might not have been atomizing the lacquer fine enough trapping air in it.
 
Messages
383
Location
Grand Rapids, MI
Once again I am super late on this one, but I thought I would chime in just to add my experience.

I use a pretty good HVLP compressor and gun made by Apollo, 4 stage. I have had problems with microbubbles in high viscosity finishes as well as color coats with high solids content. This has been the case for me in both lacquer colors and some water based colors. The general issue has been poor atomization.

From what I haved learned through personal experience, and the info one of my finish suppliers explained, the microbubbles are a result of how the finish material is laid down. When I have trouble with atomization I, and many others, try to compensate by laying on the finish a bit heavy. I think "A heavier coat will allow for longer open time, thus more time to flow out and release any bubbles", but evidently it doesn't work that way. Properly atomized thin coats seems to be the way to achieve "spray finishing nirvana"....regardless of the type of finish. Of course, the temperatures of both the workpiece and the spray material are factors in the outcome as well.

Anywho, I have found that poor atomization is usually the culprit any time I get microbubbles.

Regards,
Hutch
 
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