Refinishing sire bass and filling cavities

[brickers]

I have a sire jazz bass that I routed some wood out of for new pickups. I’m considering routing out yet more wood for different pickups. Sooner or later I want to repaint the body and fill the unused cavities and I’m just wondering the best way of doing that. The plan so far is to fill the cavities by gluing in wood blocks, lightly sand most of the body, and completely sand the front, then use car paint spray cans for the refinish. My concern is that over time there might be some join visible on the front if there is wood movement - I’m going for a pickguardless look. Is it worth finding some very thin sheet wood to glue over the front? For example Hobbycraft have sheets that are 1/32 of an inch thick. 
 

Does anyone have any experience of refinishing sire bodies? Are they known to be polyurethane? And if so am I right in thinking they can be painted over as long as they’ve been sanded to give the paint something to hold onto? Would this apply to the headstock too - I’d like to match the body colour and I’ve GOT to get rid of that terrible shape…

[BlueMoon]

1 hour ago, brickers said:

and I’ve GOT to get rid of that terrible shape…

This would be the most important thing on my list........being the totally shallow creature that I am.

[brickers]

4 minutes ago, BlueMoon said:

This would be the most important thing on my list........being the totally shallow creature that I am.

Absolutely. Takes a swathe of inexpensive basses off my shopping list, sadly. But I cannot get over it since some Canadian on talkbass compared it to a moose head

[MichaelDean]

Just now, brickers said:

But I cannot get over it since some Canadian on talkbass compared it to a moose head

That kinda makes me like it more 😅

 

They're definitley going to be poly, so yes, you should be able to scuff it up and paint over the top of it.

[brickers]

25 minutes ago, MichaelDean said:

That kinda makes me like it more 😅

 

They're definitley going to be poly, so yes, you should be able to scuff it up and paint over the top of it.

Thanks Michael. 

[tauzero]

On 18/06/2025 at 08:07, brickers said:

Would this apply to the headstock too - I’d like to match the body colour and I’ve GOT to get rid of that terrible shape…

 

Sire have actually come up with the solution to that themselves.

 

[JPJ]

Shrinkage is almost inevitable. One of the best luthiers/refinishers in the business filled an aftermarket battery compartment on a bass before refinishing and even he suffered from shrinkage or print through showing the outline of the filled area. There are ways to avoid this using a skim of epoxy filler, but this will add weight, definitely affect resonance, and may itself crack down the line. A safer method might be to veneer the front of the bass after filling the cavities, this would probably be my preferred method but then you have to deal with the edge of the veneer, itself another challenge. 

[brickers]

Thanks @JPJ  

 

my current plan, created with the help of ChatGPT and to be validated by the lovely people of this forum is to fill the cavities with wood blocks and wood glue, then epoxy glue a veneer over the entire front. (Using epoxy because it’ll glue both wood and polyurethane) I was wondering how to deal with the edges without either dulling my nice chisels, or sanding ineffectively at it and potentially sanding the existing body because it’s possibly softer than the epoxied veneer edge. I also hadn’t considered cracking though I’d hope that as this would be a thin glue layer that might be mitigated. This is pure speculation though

[JPJ]

15 hours ago, brickers said:

Thanks @JPJ  

 

my current plan, created with the help of ChatGPT and to be validated by the lovely people of this forum is to fill the cavities with wood blocks and wood glue, then epoxy glue a veneer over the entire front. (Using epoxy because it’ll glue both wood and polyurethane) I was wondering how to deal with the edges without either dulling my nice chisels, or sanding ineffectively at it and potentially sanding the existing body because it’s possibly softer than the epoxied veneer edge. I also hadn’t considered cracking though I’d hope that as this would be a thin glue layer that might be mitigated. This is pure speculation though

Sounds like a good plan to me. My reference to epoxy cracking was it terms of a layer of filler rather than an epoxy glue that you are proposing with veneer. My only concern with your method is how well the edge of the veneer/epoxy will feather back to the original finish, before you apply your new finish. But, if you intend using automotive style poly rattle cans, Halfords fine filler spray might be enough to mask the join.

[Andyjr1515]

I've never tried applying veneer with epoxy (if I was doing this, I would strip it all down to wood then use the PVA 'iron on' method I've described in a number of past threads.  However, there are both advantages and disadvantages of this too so epoxy isn't such a bad thought).

 

But, assuming this is the standard flat-topped Sire Jazz, to use epoxy, I would be tempted to use a vacuum bag (like skate-boarders use or folks who want to store quilts in their loft). 

- I would cut the veneer a couple of cm large all-round and use a decent medium set epoxy (I think I would probably use Z-poxy Finishing Resin). 

- the veneer I would use would be close-grained, non-figured (the figured will likely split in the process).

- with luck, the vacuum will not only help you achieve the close, flat bonding, but also start to curve the veneer a touch round the edges

- when set, the excess veneer would be cut off with a single-edged razor or scalpel (must be super-sharp) from the top laying the blade from the top and using the curve of the top to use as a 'summit' for the blade to have point-contact only

- then I would sand along the line of the joint with a sanding block, starting with something like 240 grit and finishing with 320 or finer

 

I'll try and find some old pics of some of the things I'm talking about

[brickers]

That’s a really great recommendation, thanks. I guess part of the challenge of this is ensuring just the right amount of epoxy. I’d presume that I’d want to err on the side of less rather than more so that I don’t have to deal with the dried excess? I can always trim back to the well-glued parts and use a filler if there’s a touch too little. But ideally this is minimal

[Andyjr1515]

With luck, your Jazz body would come out of the vacuum bag a bit like this:

 

Then, ALWAYS cutting across the grain and not along it, you use the curve of the body sides as your blade guide:

 

 

After some careful sanding along the line, again, across the grain line and not into it, it should blend in pretty well:

[PaulThePlug]

Sage advice from our own @Andyjr1515 - He really knows his onions.

 

[Andyjr1515]

5 minutes ago, brickers said:

That’s a really great recommendation, thanks. I guess part of the challenge of this is ensuring just the right amount of epoxy. I’d presume that I’d want to err on the side of less rather than more so that I don’t have to deal with the dried excess? I can always trim back to the well-glued parts and use a filler if there’s a touch too little. But ideally this is minimal

Well, the worst thing is if there is any area with not enough...that patch will bubble and raise with the moisture of atmosphere/subsequent finish spray/etc.  You will be sanding the joint line in any case to use the epoxy in the joint to blend the veneer/joint/original finish, so a bit of squeeze out isn't the end of the world assuming that this is intended to be sprayed afterwards in any case.

[Andyjr1515]

1 hour ago, PaulThePlug said:

Sage advice from our own @Andyjr1515 - He really knows his onions.

 

Most kind...but does Andyjr1515 know his epoxies from his onions??  Jury might be out 

Edited 4 hours ago by Andyjr1515

[brickers]

Amazing advice - thank you again. Looks like you did a great job!

[Andyjr1515]

33 minutes ago, brickers said:

Amazing advice - thank you again. Looks like you did a great job!

It was certainly an interesting veneer!

 

This is how the final thing came out:

[PaulThePlug]

@Andyjr1515 Don't be shy... post a link to your web site. The finished articles are great... but it's the work and attention to detail that amazes me.

Edited 3 hours ago by PaulThePlug