Brittle Finish Why?

[thirdstone]

I have a clear acrylic lacquor finish on a guitar that is about a year old and the problem is that any light/medium knock on the side causes the finish to chip rather too easily. Its too late now to fix it but does anyone know what went wrong so I can get a tougher finish next time?

kev

[Setch]

I'd guess at poor adhesion to the unlying surface. This means it's much easier for the finish to chip, since it doesn't have to break it's connection to the surface, just to the area of finish next to it. Thnis could be caused by an incompatability between the sealer/grain filler and the final finish, or between stain and top coat. The only real way to avoid this is to use tried and tested finishes, whether this means doing your own test panels and waiting a year to see how they stand up to time, or sticking with finishes which are already widely used and understood.

[thirdstone]

I'd guess at poor adhesion to the unlying surface. This means it's much easier for the finish to chip, since it doesn't have to break it's connection to the surface, just to the area of finish next to it. Thnis could be caused by an incompatability between the sealer/grain filler and the final finish, or between stain and top coat. The only real way to avoid this is to use tried and tested finishes, whether this means doing your own test panels and waiting a year to see how they stand up to time, or sticking with finishes which are already widely used and understood.

Yeah I think you are right. I had a terrible time with this spray job and I had to resort to using a sealer that was untried with the lacquor. Thanks

[another doug]

My first lacquer finish was brittle like that. Turns out I sanded to too high a grit before spraying.

[thirdstone]

Thats interesting, I sanded down to 1000grit before the sealer went on . I can't remember what I sanded the sealer down to, but it would have been at least 400 but more than likely 600-800 grit.

For this instance I still suspect the first theory.

Kev

[suicidecustom]

i just read in a woodwoeking mag recently that sanding the wood to anything higher than 220 - 320 grit does absolutly nothing as far as making the grain/figure look better, infact it made it worse in most cases. in their tests they got best results between 220-320 grit. sanding to 1000 before sealer may be the problem, you never know.

[Mattia]

1000 grit paper is verging on polishing. On Maple, I tend to go to 400, seal (shellac), scuff with 320, shoot topcoats. On most dark woods, 220 grit with the grain is more than fine enough.