Double Bass Roth project bass

[Bugeyed Earl]

So I wanted to start a thread to have a place to document the process of repairing a bass I picked up at the end of last year. The bass spent a number of years sitting in a hot south Florida garage, and the climate has taken its toll, but fortunately the termites have left it alone. Based on the remnants of the label and with the help of other TB members, I worked out that it's a Roth, but I don't really have a clue about its age. Apparently these were mostly student grade instruments made by Englehardt.

It's pictured here without strings, but it came with the tailpiece, bridge, and soundpost, so at least it's complete.

Here's the bad stuff:
The neck has been repaired, and there are a couple of screws through the fingerboard.
When the fingerboard was reattached, it wasn't lined up perfectly, but I'll live with that for now.
It has one ugly repair on the left upper rib, there might be some kind of putty in that one.
The top is starting to delaminate, but it doesn't look too extensive. Plys all seem to be intact at the F holes.
The back is delaminating pretty badly, this is what I want to tackle first.

I'd continue rambling, but here are some pics instead:

 

[Bugeyed Earl]

So I understand that removing a back is a bigger job than popping the top due to the critical neck/button relationship, but I definitely need to get inside this thing to patch the layers of the back that are separating. I'd like to get some pics of all the inside surfaces before I proceed, so I'm thinking about cobbling together a remote switch for my cell phone and devising some way to maneuver it around inside. But until then, here are the first pics I took of the innards. The top seems like it's fairly sound, it's mainly the back that's shredded.

 

[KUNGfuSHERIFF]

Pop the top, glue up the splitting, use magnets as clamps. Not the end of the world.

 

[powerbass]

The delaminating ply's are my biggest concern, this could imply glue failure or inadequate amount of glue when it was fabricated. James Candino would be a better resource for info on that.

 

[Bugeyed Earl]

So this is the first time I've seen the inside of the top, it actually looks pretty good. Bass bar seems pretty well attached. That back laminate though, that's just awful! I'm fortunate to be near Constantine's Woodworking supplies, I should be able to get some good veneers from them to replace the worst bits and it looks like they're still operating during the pandemic.

I've got some unistrut that I can use as big clamps inside the body, but not sure I'd be able to get them into place quickly enough before the glue starts to gel.

 

[Bugeyed Earl]

Pop the top, glue up the splitting, use magnets as clamps. Not the end of the world.

Thanks for the magnet suggestion, that would be less cumbersome than my clamp idea. There's a section where the innermost ply has shrunk and split along multiple lines in the grain. If I were to just glue it all down, it looks like there would be some gaps. Do you think it would be better to splice in a new piece of veneer in that area?

 

[Steven Ayres]

It appears to me that the back has been off previously, and this is your main concern, so taking that off to work on it makes more sense to me. Removing a ply back requires some care to prevent more veneer loss. Regluing the loose veneers inside may not come out perfect, but it's not really important to the bass, as long as the back is firm enough to resonate more or less evenly, with no loose bits to cause buzzes, and you don't have obstacles to setting the post.

I use squared-off plastic clothespins for edge delamination like this.

I'm under the impression this is made in Czechia OEM for various vendors. Neither this nor any other Roth-branded bass was made by Englehardt.

 

[Bugeyed Earl]

It appears to me that the back has been off previously, and this is your main concern, so taking that off to work on it makes more sense to me. Removing a ply back requires some care to prevent more veneer loss. Regluing the loose veneers inside may not come out perfect, but it's not really important to the bass, as long as the back is firm enough to resonate more or less evenly, with no loose bits to cause buzzes, and you don't have obstacles to setting the post.

I use squared-off plastic clothespins for edge delamination like this.

I'm under the impression this is made in Czechia OEM for various vendors. Neither this nor any other Roth-branded bass was made by Englehardt.

Thanks for the advice Steven! The potential for buzzing is my main concern with the back, I believe there are multiple layers that have come unglued to some degree and it's going to be a challenge to get all of them secured. I don't really see the signs that it's been off before though, there's a layer of ply that's still firmly attached to the rib all the way around. I've seen several warnings that removing a back is a riskier proposition than the top, that's why I thought I'd take the more accepted approach. If I could remove the back without ruining it, I'm sure I could do a better job of making it solid again, so I'd love to learn that it's an option.

As for Englehardt, I based that on what I've read here on TB, but I wouldn't be surprised at all to learn it's an import. The original label is totally pooped up, but I can see traces of "made in USA" on it:

Here's another Roth (not mine) with a label that survived: