I have two bubinga steel string guitars that were left in a hot car & came out with hundreds of little, pimply blisters all over the filled wood, but not the spruce top.  The guitars are about a year and half old, and the wood was over 40-years old when they were made.

They were sealed with shellac, filled with StewMac's Colortone waterbased filler:
sealed again, then sprayed with McFadden's Lacquer.


I've never seen anything quite like it & since this is the first time I've used this filler, I suspect it may be partly to blame (alongside the idiot who left them in the car). The unfilled spruce came through the ordeal just fine.  I'm wondering whether anyone else has had experience with this filler and/or had similar problems.


Also wondering how to do the repair. Can I just sand it flat & shoot new lacquer over top? Use Cellosolve?  I'd hate to have to take it all back down to bare wood & start over again, but will so if necessary.




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I haven't ever used this particular filler, but I've seen the effect you describe on many guitars, so I suspect most fillers will expand if they get hot enough. The big question is will it shrink back over several years? This might come back to haunt you again. . . .

Call Stew-Mac and get their advice; and make the customer sign a "no guarantee" statement.

p.s don't use  filler again.........

Offgassing from the wood, I would think.  Or from air trapped under the filler; in my experience (limited, since I stopped using waterbased filler after trying it on two guitars 10 years ago) waterbased fillers tend to bridge the pores.

Just curious-- what are you using now?

I was thinking of trying LMI's micro-bead acrylic paste filler. but after reading your comment, I don't know.

Has anyone had experience with that?

That's the product I would never again use.


I usually use epoxy or old-fashioned silex/solvent stuff like Pore-O-Pac.  I have had some success recently with spackling compound and dry pigment; that is water based, so I guess I lied.

Best sealer is good ol' shellac. Don't use that filler crap!

I get a high quality shellac from

I agree with Chris. I use Bull's Eye Seal Coat Clear Shellac. I believe any de-waxed shellac will do the job.




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