Short version: Should there be any issues with a finishing regimen of Shellac->Solvent-Based Grain Fill->Shellac->Nitrocellulose Lacquer?
I have been a long time reader, but this is my first post. I have recently taken to doing antique grand piano restorations. My current specimen is a 1931 Mahogany Piano. While I have had great successes using modern products on other woodworking projects, I wanted to stick to using more traditional 'non-curing' methods for pianos so as to make repairs easier in the future.
I went through the full refinishing and stripping process, and was starting to wet sand and rub-out the lacquer where I encountered an issue where the finish started flaking. (I nearly cried as this thing looked SO good). I've since stripped it all back again and started over, thinking, perhaps, it was a fluke.
This time I did a couple test pieces being careful each step of the way. Same result.
My steps:
1) I've taken everything back to bare veneer using chemical strippers, scraper, brass brush, and steel wool. (Finishing with a scrubdown of a mix of Lacquer Thinner, Alcohol, and Naptha to make sure it is totally clean.)
2) Next I stain using Old Masters Fast Dry Oil-Based Stain (Rich Mahogany Color)
3) Spray on a wet washcoat of dewaxed shellac (1 lb cut), made within the past 3 weeks from fresh flake and alcohol
4) Grain Fill with Mohawk Black Grain Filler (applied with plastic putty knife and burlap)
5) Once dry, light buffing with Steel Wool to remove any leftover filler
6) Sprayed Wet washcoat of 1 lb dewaxed shellac
7) Multiple sprayed coats of Mohawk Nitrocellulose Piano Lacquer
I have tried two different cans of stain (one purchased 1 year ago, one purchased recently), two different brands of shellac (one purchased a year ago, one purchased this spring), two different orders of grain filler (one purchased a year ago, one purchased recently), and I have used two different orders of Piano Lacquer (ordered 2ish months apart from each other, last fall.)
I have attached an image of what I'm describing. I tried very hard to swab the chipped areas with various solvents to determine between which layers the failure was occurring. I THINK it is somewhere between steps 3 and 7 above (shellac->grain filler-> shellac ->lacquer) but it is really hard to tell as the black grain filler tends to dissolve easily and make it hard to determine where the failure actually is.
Does anyone have any thoughts or suggestions?
Finish Problem.jpg
Link to Google Photos
Thanks,
Aaron