Lacquer Defect

Please put your pickup/wiring discussions in the Electronics section; and put discussions about repair issues, including fixing errors in new instruments, in the Repairs section.

Lacquer Defect

Postby Philip Secrist » Sun May 22, 2016 1:31 am

I had a tight crack in the back of a dreadnought I am building that I thought I had adequately repaired and filled before finishing. I applied the finish, let it cure for 15 days, and sanded and buffed out the finish today. A few hours later I could see the crack line subtly in the finish. I am giving it to a friend in 12 days. Is it better to wait another 12 days and then level the area again, or should I apply lacquer to the crack line (with a small brush) now to build up the lacquer, let it sit the 12 days and then re-level? Which is the best method to minimize the risk that crack line will show up in the lacquer?
Philip Secrist
Posts: 48
Joined: Tue Mar 06, 2012 5:24 pm

Re: Lacquer Defect

Postby Todd Stock » Sun May 22, 2016 7:41 am

This is likely just the differential drying rate between the new lacquer and the less new lacquer. Usually just a case of waiting as long as possible before sand/buff, and avoiding a lot of heat build-up during buffing. So yes - finish up whatever else there is to do, then hit the back again just before delivery. If the finish on the back is thick enough, don't touch up with more lacquer - just allow to dry longer and sand/buff level.

If I was concerned about cutting through to sealer while sanding and buffing, I'd drop-fill the crack area and shoot a flash coat (50/50 lacquer and thinner) on the back...that will get enough lacquer on the crack to allow scraping and the differential shrinkage between the lacquer will be minimized.
Todd Stock
Posts: 394
Joined: Tue Feb 28, 2012 7:57 pm

Re: Lacquer Defect

Postby Philip Secrist » Sun May 22, 2016 10:56 am

I filled the crack (I thought) with super glue at the bare wood stage and then applied finish. I think I have enough finish to level one more time in about 12 days. Thanks.
Philip Secrist
Posts: 48
Joined: Tue Mar 06, 2012 5:24 pm

Re: Lacquer Defect

Postby David King » Sun May 22, 2016 5:22 pm

Super glue shrinks like just about every other finish known to man.
David King
Posts: 2448
Joined: Sat Jan 07, 2012 10:01 pm
Location: Portland, OR

Re: Lacquer Defect

Postby Michael Lewis » Sat May 28, 2016 3:33 am

Newer lacquer shrinks more than older lacquer, and as long as there is ANY solvent left in the finish it will shrink when the solvent leaves. If you can smell it it will shrink. You really need more time, weeks, not days.
Michael Lewis
Posts: 1446
Joined: Thu Jan 12, 2012 1:22 am
Location: Northern California USA

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