Official Luthiers Forum!

OK, I'm buffing out my finish and I've run into an odd problem. On the soundboard I've got, apparently, two different batches of spray lacquer and they don't entirely match in glossiness. So the profile of the one layer of lacquer that shows is of lower sheen than the other. So when buffed out one can see a slightly duller area around the rosette in areas than on others. I'm struggling to explain as I can't photograph it. Think of a wave on the shore, the sand isn't even all across. Same with my finish. It's subtle but quite visible.

So do I need to strip the whole thing. Oh please don't say yes. I can't level and spray more as I think I'll deaden the wood if I spray enough to get a solid even coat with one can of lacquer.

Normally when restoring something I'd just add more as it won't affect the overall look, but here it may likely affect the sound. I need some help.

Ideas?

Thanks! Joe

Hi Joe,

If it's really just that the two lacquers have different glossiness, then you should be able to re-spray the whole thing with one thin new coat of lacquer, polish it, and you're done. The new all-over coat should burn in to the old coats. However, from your description of sand on the shore, it sounds more to me like the two lacquers have different COLORS, and that's what is actually making it stand out. If it's the color that doesn't match, then no amount of extra coating/polishing will solve the problem, and you will have to sand back to wood and start over. Any help?

Cheers,
Dave F.

_________________
Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

Did you apply a sealer on the bare wood under the lacquer? Sounds like you sanded through to the sealer to me.

More info on the process and some photos might help.

_________________
http://www.chassonguitars.com

Thanks guys. Two answers:

Several coats of sealer.

The concept of different color didn't hit me so I looked again. It is the same color but literally a different level of gloss. This is wet sanded to 1500. I think because it is the same color it doesn't show when photographed. I tried many angles and can't get it to show up at all. It looks perfect in the photos.

I'm worried about the thickness of the lacquer, thus the worry about coating yet again. Should I be?

Hi Joe,

So it's not the color of the lacquer then - phew!

Maybe you sanded some areas more than others after the sealer coat/s (or over-sanded them, like Kent suggested)? If that was the case, then those areas may have soaked up the finish and given you this not-so-glossy look? If so, then the solution is the same as I suggest below....

How many coats of lacquer did you put on top of the sealer? Were they thin coats? What kind of spray equipment did you use? It sounds like you used pre-pressurized cans = expensive . I'm just trying to get an idea of how thick the finish is already. Can you measure the thickness (with a digital vernier at a finish edge, say at the bridge or neck)?

What was your leveling sanding procedure? It could be that you didn't flatten the finish over the entire area (you know, keep sanding until you can't see any more shiny spots before moving on to polishing). That would leave areas that were less glossy than others. If you look across the finish at an oblique angle with a light behind the instrument, can you see shiny spots/islands in the not-so-glossy area? If yes, then what I'd do is go back to 600 grit and wet-sand the whole instrument again.

That's what I'd do from here if I were you. Go back and re-sand it starting from 600 grit, making sure that it's absolutely flat with no shiny spots, then move on up through the grits to 2500, then polish it on a buffing wheel. Basically, re-flatten and re-polish it from scratch. If it still has the problem, then you'll have to sand right back to bare wood and start over or you might get away with adding a couple more coats and re-leveling/polishing again....

Cheers,
Dave F.

_________________
Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

Yea! It was indeed low spots in the sanding. So as suggested I want back to 600 and resanded. I sanded through the grades and polished, the funky wavy look is gone. As I wet sanded with 600 I sanded a bit, then wiped things clean. The "wavy" areas were indeed shiny. Hummm, I thought I was more careful than that. I guess not.

Thanks guys!

P.S. I'm just getting into this, so I'm a novice with instrument building. I really appreciate the thoughtful and kind suggestions. What a great forum!

Joe

So you have two different sheens of lacquer on the instrument? Which level is the high gloss level? The lower from the sounds of it. If you sprayed a low gloss lacquer over the high gloss you'd never get a high gloss finish as there are flattening agents in the low gloss material that will refract the light differently hence causing the low/no gloss look. Also sounds like the reason you got some spots glossy and other not is because as you sanded, you removed layers of the low gloss (really you removed the flattening agent) and you cut down to the high gloss level. Mind you the way lacquer works, all levels burn into each other but I sort of doubt that the flattening agents work down into the lower levels.

If you find more dull spots showing up, you may have to remove all the finish and start again, using only the sheen you want.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Thanks Rod. I think that is not the case here. All the lacquer was the same product, but I do think I ended up with low spots after my first sanding/polishing series and I don't think I cleaned up well enough during the process to discover it. The low spots were around some fancy work I did around the sound hole and don't think I sanded quite aggressively enough to level that area.

But, the information shared is great and will certainly be helpful to me and others as we learn the reactions of the materials we are using.

Thanks! Joe