I am in the middle of a rebuild of a 1935 Gulbransen P46 (petit baby grand). The piano was taken from a warehouse where it has been stored in a humid environment (PA) for a decade without climate control. The soundboard appears to be intact without any serious faults, but the coating (lacquer) is discolored, has cracks, and is in really bad shape. I read in a repair book that one should not use lacquer remover as it can damage the soundboard. It recommended scraping off the finish. I am concerned that I cannot scrape off the finish fully without doing at least minor damage to the wood below. Hence the question: Should I scrape this or use lacquer remover? Any tips? Thanks!
Learn how to sharpen a scraper and how to use it. There are paint scrapers and cabinet scrapers. If you use a cabinet scraper, you hold it with both hands and flex it slightly so the work is done mostly in the middle. That way the ends don't gouge the wood. Yes, stripper will stain the soft wood.
One thing that makes scraping (and planing) without damaging the wood easier is to ease off the corners of the scraper blade slightly. This keeps the corners from digging into the wood, and if you go a little bit sideways, you are not digging in across the grain.
To get into the corners, a triangular blade with one sharp corner will do the job.
I do not know why people who talk about sharpening planes say you should have a gentle curve. That is harder to do, and does not leave a flat surface.
Learn how to sharpen a scraper and how to use it.
For the record, learning to use them is easy. Learning to sharpen them so they're worth using isn't. YouTube is your friend.
Thanks for the tips! Scraping it is.
Soundboard finishes are usually extremely thin. They usually come off with just a little solvent on a clean rag, ethyl alcohol works fine. Clean the board with detergent first, so that dirt is not smeared into the wood. It is a little like cleaning dried cool-aid off of a tabletop. It does not come off instantly, but it does come off readily. And, because the solids are carried away almost as soon as they are softened, there is very little penetration of the surface. Just keep changing your rags, and a clean, ready to sand surface can be had in minutes. Acetone works very well, also; but I am less intimidated by alcohol, for some reason.
Excellent advice. I managed to remove a good 90% of the coating yesterday by scraping, but the alcohol technique that you mentioned also works very well. I will use this for the rest of the edges and tricky spots. Do you have any advice for the new coating? I have read that standard lacquer is preferred. I have some precatalized MagnaMax lacquer which I am tempted to use. The potential downside is that when I'm done it will be as hard as a rock. Is this a suitable method or not?
I think that the "hard candy shell" effect is to be avoided. To talk like an audiophile, it may boost the high end and give an illusion of volume, but it comes at the expense of the mid-range and any warmth in the bass. MagnaMax gets shattery; You might want to get a quart of plain nitrocellulose.
We french polish our boards. It is a lot of elbow work, but it is such a beautiful thin finish, the effort is well rewarded.
Historical finishes were not applied this way, however; they were brushed on.
Historical research leads us toward sandarac as being the most likely original material.
We are experimenting to find the right application technique.
Just as a counterbalance to the proposed methods as i have done neither scraping or French Polish. I have removed finishes for years with Store bought stripper, neither did it harm the wood nor discolor it. After stripping, i clean it with lacquer thinner, then do a sanding before spraying. 1 coat sealer, 2 coats finish. I have tried many finishes and i now use Mohawk Piano Lacquer. After the finish cures, i prefer to rub it out with pumice and steel wool, then polish. I always thought the glossy finishes looked cheesy.
I have a family member in Seattle who also does it about the same way except he coats the soundboard with an epoxy wash before applying a finish. On older boards this is may be worth doing to help clean up the tone, as many older boards can have a muddy sound to them.
Thanks for the excellent advice Craig and Chris!