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French polish cracks 3 months post build

Posted: Thu Jun 18, 2015 3:28 am
by bearskindrum
Hi All two sets of random "cracks" or splits have appeared in my guitar 3 months after finishing (see photos)...they are in two areas only on the top, with none occurring on the back, sides or neck....95% of the top is fine with these collections of cracks appearing on the right hand upper bout near the finger board and on the left hand side around 1/4 of the rosette everywhere else seems fine.... I tried level sanding with 1500 and 2000 grit paper and then Novus polishing which seemed to fix it, but a few weeks later they have returned...really frustrating! so Should I fine sand and then spirit off or FP again over these crack thereby filling and then re levelling? The polish was too thick in these areas initially but they did seem to respond to levelling and repolishing many months ago.
I don't want to have to go back to bare wood again as I don't think that's necessary(yet) but would really appreciate some input especially form the PF gurus...

Cheers Mark

Re: French polish cracks 3 months post build

Posted: Thu Jun 18, 2015 6:54 am
by Danl8
It is possible that the base layers hadn't sufficiently dried when the top shellac coats delayed full drying of the EtOH solvent. Over time it does dry and shrinks. Also the freshness of the shellac itself might be a factor in complete drying. You might consider letting it go for a while until the checking is stabilized/stopped, then fix it. If it were my situation, I would lay in shellac (initially maybe a heavier cut, 4#?) over the area with sanding to level and then resume polishing. (disclaimer: I am no expert)

Re: French polish cracks 3 months post build

Posted: Thu Jun 18, 2015 8:01 am
by B. Howard
bearskindrum wrote: The polish was too thick in these areas initially but they did seem to respond to levelling and repolishing many months ago.

This is the result of putting down too much shellac at once without enough pressure. It is a waiting game now. You cannot fix this until the shellac has completely hardened, probabally another 3 -6 months until the film completely settles. At which point you can drop fill the cracks with a thick shellac and then level and polish.

Re: French polish cracks 3 months post build

Posted: Thu Jun 18, 2015 3:09 pm
by bearskindrum
thanks guys for you advise.... I will wait until it stabilises and the repair as suggested...many thanks

Mark