Q: My nitrocellulose acoustic guitar finish is now horribly squeaky. I have owned it for five years with no problems, but now, any light touch produces the sound of new tennis shoes on a basketball floor. It happened the day after having wiped the guitar with Old English lemon oil that may have contained some vegetable oil. I tried cleaning it all off with naphtha, then turpentine, but no improvement. The unfinished fretboard is just as bad. Ian Davlin at Gruhn Guitars thought the finish may have been chemically altered somehow, so I tried using some of the polish they use but the squeak just got louder, including the fretboard.
A: Short of seeing the piece, I can’t be sure some important fact was not innocently left out, but taking your letter at face value, I will share some information that might help you figure out what’s really going on.
Clean lacquer is not squeaky. About the only thing that is squeaky is a partially cured long oil finish. Putting a drying oil, in particular one of the slower drying oils such as walnut oil, on a film finish like lacquer can form a surface film that will squeak. As a rule, nut oils are drying oils; vegetable oils and mineral oils are non-drying oils.
Most commercial formulators know this and avoid using anything but non-drying oils in their mixtures. However, there are a wealth of guitar polishes out there created by well meaning but less informed fabricators. I doubt a company like Old English would make such an error, but it is entirely possible that someone less experienced in formulating might. If that is your problem, the solution is to scrub it aggressively with mineral spirits on a gray nylon abrasive pad, wiping with clean paper shop towels until you are back down to nothing but lacquer. It may not be easy; cured or partially cured drying oil is not easy to remove, and it is quite possible to destroy the lacquer finish in an attempt to clean it. Once back to lacquer, you can recoat or simply repolish the guitar with automotive polishing compounds, assuming it was a gloss finish. Because of the risk and difficulty, this is really a job for a repair luthier skilled in finish repair.
The other possibility is far less likely, but I will mention it just to cover the bases. Some oil, including sebaceous oil, which your skin exudes, can migrate into nitrocellulose lacquer where it acts like a plasticizer. If enough migrates, the finish itself gets softer and more rubbery, and can start to squeak. The easy test for this is to press a thumbnail into the finish. Normal nitrocellulose will not take a nail impression easily; over plasticized nitrocellulose will.
Michael Dresdner
straight talk about wood finishing
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