Regal banjo cupping mots fingerboard

[Ian Pender]

I have an older Regal banjo with a mots fingerboard that is starting to cup. Upon initial inspection, it appears that the fingerboard is masonite with celluloid glued to the face. The celluloid is starting to shrink, causing the fingerboard to cup and pull away from the neck, working frets loose in the process. I'm wondering if anyone on here has had any success flattening these out. I certainly don't want to just apply heat. I've got a few ideas, but I'd like to hear from someone who has a bit more experience with these instruments.

[Frank Ford]

As we said in the 1950s, "Duck and cover!"

Well, that's what those fingerboards do.  The fret slots are cut right through the celluloid which shrinks, pulls away and cups the fingerboard.  Frets get loose, necks bend forward.

I think the best technique is generally so painful we hardly ever do it.  We'll carefully take all the frets out, pry off the celluloid pieces, level the maple or other wood underneath, regluing and straightening the neck as needed.  Then, we'll reglue all the pieces with Titebond, clamping everything up nice and flat.  Once that's done, refretting completes the job.

I can never think of a high enough price to estimate the cost, so it's a "time and materials" job around here. . .

[Kerry Krishna]

I had to do this job on a Stromberg/Voisinet a few years ago. Then time and effort I put in was .... wayyyyyy too much, and the refretting afterward was a total nightmare. It's a huge job, but if you have lots of time and patience (numbering the MOTS, carefully pealing off the MOTS, cleaning the MOTS, flattening the board, and reattaching the MOTS, , then putting binding back on, well you get the idea.

 The one suggestion I would make is to get some metal feeler gauges and put them into the slots to position the MOTS when gluing back down, otherwise, it's a fretboard skating rink!