Lacquer defects on figured maple

[Peter Wilcox]

This concerns a quilted maple top. I sand to 320, raise the grain, apply dye, sand back, wipe on a coat of shellac, spray on 5-6 clear coats of Watco brush-on lacquer thinned 1:2, level sand, then 6-8 more coats of clear, sand to 2000. Smooth and flat. Over the next week or so, a reticulated pitting pattern appears on the surface that follows the figure pattern of the wood. It seems to me that the lacquer is drying/shrinking at different rates over different parts of the grain.

The back of the guitar is natural alder and has received the same lacquer finish at the same time as the top, and remains smooth. I suppose if I wait a certain amount of time (weeks/months?) for the lacquer to completely harden, and sand back level it will stay that way. Is this a known problem with figured maple?

[Barry Daniels]

I am not sure why maple would do that, but this is why most finishers who use lacquer let it cure for one month before final leveling.

[David King]

It's possible that the maple will keep moving around for years to come. I'm assuming this is a solid body guitar?

[Peter Wilcox]

I hope it's differential curing of the lacquer for some reason, and it will reach an equilibrium sometime in the not too distant future. It's a solid body guitar, but the maple is only about 1/16" thick.

http://www.mimf.com/phpbb/viewtopic.php?f=59&t=4095

[Michael Lewis]

The end grain will take in more 'wet' and also have more wet to evaporate. as you know lacquer can take a while to gas off the solvents.

If that surface in the pic was leveled and then this pattern appeared I wonder about the spray pattern your gun delivers. It looks like droplets rather than mist.

[Peter Wilcox]

If that surface in the pic was leveled and then this pattern appeared I wonder about the spray pattern your gun delivers. It looks like droplets rather than mist.

The back was sprayed in exactly the same way at the same time, so if this were the case I'd expect it to show the same. And although I couldn't get a good picture, the pattern follows the figure of the wood. So I believe, as you say, it has to do with the different absorption and outgassing of the end grain versus the flat grain. Maybe the droplet pattern reflects the action of each pore in the wood.

[Steven Smith]

Don't know if this is useful to you or not but I saw something similar on the maple on a mandolin I sprayed with Royal Lac. Seemed to be caused by the finish shrinking. When all was done it leveled out just fine.

[Peter Wilcox]

Thanks Steven, that looks exactly like what's going on on mine. I'm not familiar with Royal Lac, but from a google search it seems to be a shellac formulation.

Anyway, when you say "when all was done it leveled out just fine", do you mean it leveled out on its own with time, or did you have to keep level sanding multiple times?

[Steven Smith]

It did not level on it's own. I was a bit surprised as you were so I leveled a part of the back before my final coats to be sure it would level - it did just fine. So I just scuff sanded it and then sprayed the final, thinned, finish coats. I had no trouble leveling it out when I did my final wet sanding. I also saw the same effect on the spruce tops but FWIW where I sprayed on ebony it was as smooth as you would expect.

[Todd Stock]

Usual practice is sand between the sets of coats...I wet sand with 400 to level back to about 90%, staying off the bindings. Figured woods and softwood tops will routinely show this sort of variation, but taken care of after a level and a few additional coats to build to final target thickness.

[Peter Wilcox]

Well, I leveled it again to 1000, and then finished it. So far, so good - time will tell. I think part of my problem was the 50-60 degree ambient temperature that the finish was curing at.

The take home lesson for me is to try to be patient, and wait at least 3-4 weeks before final leveling and finishing, as Barry said in the first response.

[Michael Lewis]

It used to be said that a lacquer finish could be 'cured' in two weeks, maybe that is how Harmony did it. Now we are accustomed to much better looking finishes. I usually wait 6 to 8 weeks before final leveling and buffing.

Funny, but I am using very little lacquer anymore. Certainly I use it for appropriate repairs, but for new instruments I am drawn to the varnishes like Epiphanes clear gloss varnish, and curious about General finishes Endurovar.