Luthiers: Choice for touch up nitro lacquer?

Construction and repair of Classical Guitar and related instruments
brassrat

Luthiers: Choice for touch up nitro lacquer?

Post by brassrat » Fri Jun 22, 2007 3:32 pm

I know I can order the pint can or spray can but I only need just a little bit (like 1 oz bottle) for touching up a few deeper scratch that I can't remove with Scratch-X.

I've heard recommendations from nail polish, hobby shop lacquer to furniture lacquer.

I have a nitro lacquer finished CG. What can I use and where can I buy just a small bottle of it?

I guess worst case, I buy the pint can and just have a lot left over.

Thanks for your help

Marcus Dominelli
Luthier
Posts: 2860
Joined: Thu Mar 08, 2007 4:52 pm
Location: Victoria, B.C. Canada

Post by Marcus Dominelli » Sat Jun 23, 2007 12:23 am

Are you just going to put laquer in a few dinged spots to keep dirt and grunge from getting in the finish or in the wood? Or are you planning on overspraying larger sections of the guitar? Do you have any experience at this kind of thing?
It is so hard to give advice on this kind of thing without looking at the guitar. It is possible that you have made the assumption that your guitar has a laquer finish. Just because the guitar may not be french polished, does not mean that it therefore is a laquer finish.
If it's some form of catalized varnish, nitro laquer is not what you should be touching it up with. Even if I ask you the make of the guitar this may not be enough to determine what kind of finish it has. Ibanez guitars for example, is a trade name, not a factory; Ibanez guitars are built to different specs wherever they are made.
I am not trying to make things more complicated than they have to be. But choosing the right laquer for the job is really not what is critical here.

If you are just touching up a few dings and are not planning on overspraying larger parts of the guitar, you would be safe to use most brands of laquer. Filling small dings will not require perfect adhesion of the new laquer to the old, because you're just filling a small hole and not expecting the ding to be invisible. But if you're doing larger areas of the guitar, overspraying is something to be avoided if at all possible. Unless you really know what you're doing, you could really mess up the guitar.

Once you spray new laquer over old laquer and then try to rub it out to a gloss you'll see what I mean: Every spot where you rub through the layers of laquer will reveal "witness lines" between each coat.
It happens in the auto finishing repair world too, and explains why even small dings in the body require whole sections of the car to be sprayed. You can't just do "little spots" with laquer. It will look horrible.
In response you may say,"It's just a cheap guitar anyways." My answer then is to just leave it alone.
Marcus Dominelli

brassrat

Post by brassrat » Sat Jun 23, 2007 2:31 am

I'm sorry for not being specific.

The guitar is a Cordoba Pro-R and the US rep for Cordoba (Tornavo Music) when contacted told me that the finish is nitro poly.

The scratches that I'm trying to drop-fill are two shallow but long ones (~3"). However, they are deep enough that I have not been able to polish them out. The wood is not cracked. I checked the inside through the sound hold.

Image

The small mark just above and to the right of the bottom scratch is not a scratch. My guess is that the guitar went through a rapid temp change and the wood swelled a bit causing the finish to crack.

I was planning to drop-fill with nitro lacquer along the crack with a pin or a sharp tooth pick. Allow the lacquer to melt in. Give it a week or so, then take off the excess with a scotch tape protected razor blade, wet sand and buff.

I've read the archives on this forum as well as other guitar refinishing forums. I'm pretty handy with tools and have done small automotive refinishing so I'm familiar with paint drop-filling, wet sanding, and polishing techniques.

I was just looking to find a place where I can small bottle of lacquer and maybe some suggestions on the lacquer type and brand.

I would appreciate any pointers. Even if it's to just leave it alone. :lol:

Marcus Dominelli
Luthier
Posts: 2860
Joined: Thu Mar 08, 2007 4:52 pm
Location: Victoria, B.C. Canada

Post by Marcus Dominelli » Sat Jun 23, 2007 7:15 am

I think that might work fine. I don't think that the brand of laquer you use will matter too much.
Some of these finishes only have a very thin clearcoat over top of a tinted colour coat, so be very carefull that you don't buff through the color coat or you'll see a spot where the repair was done.
The laquer you put in the crack will not dry as hard as what is on the guitar, so be prepared for the rate of shrinkage to be faster with the fresh laquer. You might get it rubbed out flat and looking good, only to find that a week or so later, the laquer has shrunk into the crack some more.

By the way, on those polyester varnish finishes, the most compatable repair filler is thin cyanoacrylate (crazy glue). It dries to a hardness that is very close to the finish on the guitar, and so invisible repairs can often be done with some patience.
This might be what you have on your guitar. A bit of laquer thinner on a q-tip rubbed in an inconspicuous part of the guitar should tell you if it's laquer. The laquer thinner will not dissolve a polyester varnish as far as I know.
Before putting c.a. glue into a crack, remember that it can discolour the wood. It will darken rosewood more than laquer will. It can do weird things to spruce and cedar. It may even turn spruce green!!
So consider sealing the crack with a bit of laquer or shellac first, (if indeed you determine that c.a. glue is the thing to be used).
Good luck!!
Careful with the razor blade. It sounds risky.
Marcus Dominelli

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