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Lacquer is cracked after polishing


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18 hours ago, Bizman62 said:

The more liable culprit is that the moisture gets into the wood from the sides of the holes.......

Good point, also seeing as the other guitar didn't have cracks until I cut f-holes in it

"Its those f-holes gosh darn it, they're the cause of my misery!"

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  • 2 months later...

I've had this happen around volume controls.

I think its a combination of water and pressure while wet sanding and buffing. 
I've fixed this with lacquer thinner on the cracks, applied a few times, let re-cure for a week then re-spray another  coat and fill in the areas where the cracks were. 

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  • 2 weeks later...

Adding to the post-mortem -
Thoughts based on the guitar I was building where we both had the same issues at the same time:

- Cracks only on the top which was hard maple (actually I did have a very small crack or two on the back around the control cavity).
- Sprayed very heavy, and probably not enough time between coats.
- cracks were mostly around holes, though not all. Some were on the top carve and were at an angle. I had three small ones parallel to each other, but not perpendicular to the carve or parallel. These imply curing stress cracks to me.
- Cracks definitely developed after wet sanding, but some also appeared later when dry sanding but not as many.
- When I enlarged the cracks to apply solvent, the finish seemed to lift at the edges of the cracks which could be adhesion problems.
- No solvent worked on the cracks except the Cellusolve. (tried thinner, thinner mixtures, blush remover)
- The frequency of the cracks slowed over time, and eventually stopped.

My conclusions are:
- wet sanding was an issue
- too thick of layers was an issue, especially earlier layers.
- I'm questioning moisture content of the maple because of possible adhesion and movement issues
- Cracking occurred as the clear coats cured, curing took a long time because of the thickness, and was exacerbated by maple moisture content.

 

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