I built a dreadnought guitar for a friend about 3 years ago. He recently told me that after 2-3 months of playing it, that the finish became rough. I fussed at him for not telling me sooner but I don't think he wanted to trouble me with it. The guitar has Indian rosewood sides and back, sitka spruce top, and Honduran mahogany neck. I used Z-poxy resin to grain fill the sides, back, and neck. I sanded the Z-Poxy back to the wood only leaving the grain filled. I spayed shellac on the top spruce as a sealer, but did not use any sealer on the remainder of the guitar. I used several coats of sprayed KTM-9 waterborne finish for a top coat all over the guitar. It was smooth and glossy after buffing.
Now in 2018, it appears that the top coat is raised along the grain in areas where the guitar has been handled; the neck, side at right hand resting area, the side in the thigh rest area, and on the back around the chest resting area. The neck and arm resting areas are the most affected. There is also some thinning of the top coat on the spruce side around the arm rest area.
Before I tackle a refinish, I'm trying to determine the problem. There appears to be a connection between sweat and the finish. But why is it raised in the grain pore filled areas only? Perhaps the KTM-9 wasn't good because there is also a worn area on the guitar top? Possibly an adhesion problem between the Z Poxy filled grain and the KTM-9 caused by sweat?
I would like to refinish with another waterborne finish. I don't like using nitro. Perhaps a new Z-Poxy grain fill, followed by a shellac sealer coat, and Target Coatings EM6000 or EM2000? I've had good results on mandos with EM6000. I'd also consider varnish/French polish. But I assume if sweat is part of the problem, a shellac finish would not hold up.
Any thoughts?
Finish blistering along the neck grain
Finish blistering on side arm rest area
Unaffected unhandled side area
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