Q: I have a piano with what Kawai tells me is a polyurethane finish that was severely gouged. While I am a professional refinisher, I am at a loss as to how to burn-in the gouges and rub them out without having to re-coat. Is there a method to avoid the re-coating?
A: Probably not. I don’t mean to be presumptuous, but those pictures you sent with your letter just about confirm that it is polyester. That particular type of cracking is almost exclusive to massively cross linked brittle finishes, such as polyester and certain UV cured coatings, and not typical of the impact damage to polyurethane.
Sadly, I have often heard people in public relations areas, such as help line and sales reps, confuse the two terms, so unless you spoke with the finishing department, I would be skeptical.
If it is polyurethane, it’s most likely a linear urethane, the type of two part chemically reacted finish usually used on cars, but also commonly in use on electric guitars. While they can chip, break and delaminate, the pattern they exhibit is decidedly different than that of polyester. Linear urethane is admittedly hard to blend without recoating, though it can be done. That is to say, you can rough an area, spot spray and then rub to satin and get a moderately good blend. However, I must admit that it is far easier to get it looking, as you say, exceptional, if you bite the bullet and overspray the entire panel. This becomes almost mandatory if it is an off the gun sprayed satin instead of a rubbed satin.
Polyester is even more difficult to adhere to, and spot spraying will be even more difficult. It may look ok for a while, but can start to peel at the perimeter of the feathered area. In this case, I would definitely plan on respraying the entire piece. You will, of course, have to sand it all lightly to add tooth, since polyester is notoriously difficult to adhere to, even by itself. For tiny chips and damages, many repair people use cyanoacrylate adhesive to fill the small voids, as it will bond to the polyester and can be rubbed, but in this case, it looks as if the repairs may be too large for that. There are also polyester repair kits available from companies who specialize in touch up and repair supplies, but even that is difficult to hide if it is an off the gun sprayed satin instead of a rubbed satin.
I realize this is not what you wanted to hear, and I am sorry, but you sound like someone who is quite conscientious about your work quality, and sad to say, this is the best information I can give you, even if it is not the most welcome.
Michael Dresdner
straight talk about wood finishing
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