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Pre-cat Lacquer Checking (?)


ToddW
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Help please.

I sealed the solid body guitar I'm finishing with a couple of 1# cut coats of de-waxed shellac and sanded it to 320. Then I put down 3 coats of pre-cat lacquer each an hour apart per the instructions, sanded to 600g after each. I then repeated this the next day. 3 days later I sanded up through 12,000 grit and was planning to buff it later.

That was about 2 or 3 weeks ago. I worked a little on the electronics yesterday and it looked fine, but today I saw what looked like deep linear dents in the finish radiating out from the tail piece studs and a couple from the tone control holes. The feel like dents too, but I think there's a very fine crack in them.

Any idea what caused this? Clearly I have to sand to wood and redo this, but I'm clueless on the cause.

Thanks,

Todd

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Well, I think I figured it out somewhat. In sanding it off outside dusted up easy, but once I got through the outer part, the finish underneath was soft and still had a solvent smell. To the point where I'm letting it cure overnight since it is too soft to sand off easily.

So . . . guess you can put one or two coats down after an hour, but clearly I exceeded the maximum thickness. I'll sand off the top, the back and sides are thinner so I'll see how that goes, and then I'll re-coat. But clearly I'll let it cure much longer between coats!

Todd

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I've never used pre-cat laqcuer - it is a nitrocellulose product like regular lacquer?

I use a pre-cat conversion varnish and I never end up needing more than 3-4 coats, and that's with 20% thinner. It can be levelled after a day or two, but it ends up being much harder, and levels and buffs out nicer, if I let it set for two weeks. After 2 weeks you can't smell the solvent coming out.

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I've never used pre-cat laqcuer - it is a nitrocellulose product like regular lacquer?

Hi Erik,

I think it's basically a mix of some nitrocellulose lacquer and a conversion varnish. The nitro makes it act like acquer, and I would guess helps with adhesion of multiple coats. I think it also means you need to let the lacquer thinner flash off before you cover it with more varnish. I probably went too thick and too fast.

Live and learn . . .

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