Drop filling Nitro Cellulose Lacquer

[Doug Cannon]

I am using a drop fill method to fill pot holes on a pitted nitro finish. Almost all of the holes are surface marks but there are a few exceptions. Most of the methods that I have read about prefer to use a thickened lacquer with several weeks down time to allow thorough curing for leveling. My question is this: 

Would using a thinned lacquer (with more coats) allow the solvent to leach out of the lacquer sooner and if so, would that allow an overall quicker curing time? 

I'm open to other ideas, of course, but I do want to use nitro cellulose as a medium to integrate the repair properly with the guitar's finish....

Thanks

Doug

[Paul Breen]

The short answer is no. If the lacquer to be drop filled is old though, you may want to thin the first lacquer drops in each hole with reducer that has some retarder in it. Older finishes often need help to get the new lacquer to melt a bit into the old. After that go full strength, no thinning. Low humidity conditions and moving air will help the finish to cure faster but you really are best off to let it sit a couple of weeks.

[Doug Cannon]

Thanks Paul....I just thought I'd throw it out there....I did use a slightly thin lacquer to soften the first pass....

Would using the retarder by itself soften the older finish as well as the Lacquer/Lacquer thinner/retarder combination?

[Paul Breen]

Retarder by itself is not a good idea, mix it 5 - 10% with reducer if you opt to even use it. Just thinned lacquer by itself is probably adequate unless the lacquer is really old. You won't know if the new finish melts into the old until after you buff though. It will leave a witness line the shape of the holes you fill if it doesn't. 

[Frank Ford]

Retarder (or Cellosolve) will soften and prepare old nitrocellulose lacquer for best adhesion and bonding with the new lacquer.   As a matter of regular practice, I apply by spraying beyond the range over which I plan to spray new lacquer, thus eliminating the feather edge when the new stuff is leveled to the surrounding original lacquer.

For drop fills, there's less need for retarder, so I use it only if the lacquer in the area to be filled is seriously cracked up.  Otherwise, a drop fill will burn into the old lacquer and witness lines are not commonly an issue after rubout.   

After applying the amalgamator (retarder or Cellosolve) I let it dry overnight before proceeding with either spray or drop fill as appropriate.

In any situation, a filled area may take quite a while to dry - after all it's usually much thicker than a regular sprayed finish. . .

[Doug Cannon]

Thanks so much, Frank....Are there any obvious down sides to spraying retarder to, for instance, "clean up" a scuffed area (800 grit) or to help the lacquer around a Gibson logo "reacquaint itself" with the fake pearl inlay? I once notice a crazed mark (the thickness of a hair) from doing this and wondered if it was from the retarder....

Thanks for your advice....greatly appreciated!