Hello, and thanks in advance for your advice.
What approach would you take to fix a terribly deformed plywood top with a plywood bridge plate? The bridge lifted over the years, and a pronounced belly formed, leaving the top, under the bridge, quite sloped. It is not a nice gradual slope. If one were sledding on the guitar top, one would start at the back of the bridge footprint and slide to the front of the footprint.
The bridge lifted, and was successfully removed. The guitar is one from the 70's, the bridge has two bolts and an adjustable metal insert saddle. The X brace has come unglued on the treble side near the bridge, where the deformation is the greatest. The glue used has a white color.
I am quite reluctant to try to remove the bridge plate, as I am afraid the plywood top would come away as well.
Has anyone had success fixing one such as this?
Hi Elaine. You are describing very severe structural damage in a cheap plywood guitar from the 70s. It is likely that the top has delaminated in parts. Between that and the bracing failure the top sounds unfixable. You could replace the entire top, if the rest of the instrument is OK. But there is a strong chance on a beater like this that other problems coexist - bad neck angle, twisted neck, seized truss rod, worn frets, crappy tuners. In short - probably not worth the time/cost/effort on this instrument. At this point the question of sentimental value comes up ( “my dear departed mother played me and my 10 siblings lullabies on this guitar every night, I would do anything to fix it”). So I could understand if you want to try a heroic rescue for this instrument - but the reality is that it sounds like time for a new guitar.
Mark, thanks for your input.
The guitar indeed has sentimental value to the owner. It seems to be in great shape aside from the deformed top, and has lovely binding, purfling, etc. I think it will need new frets, however. As I am fixing it for the sheer fun of the challenge, cost is not an issue.
So here is my plan, sans a better idea. I am going to attempt to flatten the top, at least somewhat, by clamping a 2 X 5 heat pad inside the guitar between damp terry cloth and a caul over the bridge plate. After that has "cooked" I will clamp it as flat as possible using the bridge plate caul and a cork lined board across the top.
Assuming this flattens it somewhat, I will re-glue the loose brace, and glue a piece of hardwood over the existing bridge plate, with the grain running parallel to the strings so it resists bending as much as possible. Then I will fit the bridge to the perfectly flat top (ha ha) and glue it back on. I will leave the bolts out (yes, it had bolts).
After this, I will install a JLD bridge doctor, 'cause, why not? I fervently hope it doesn't need a neck reset after all that, but we shall see. I suspect the action was pretty good because the front of the bridge had sunk down.
What do you think of that plan?
Sounds like a plan. Getting the top wet and clamping until dry is also a way to straighten warped wood, but heat is probably more effective.
Hi, I have done this repair more times than I can remember, over the years. I have the whole process in photos of many guitars, but too many to post here. I will see if I can put it into words. It's pretty much as you explained in your plan. I have found that ply/laminated tops can be more difficult to correct as often the problem may have been caused by heat, so the top pulls up, and the glue resets in the laminations and holds the top in its new shape.
What I have done, with success, is to remove the bridge, and sometimes the bridge plate, apply heat with a hairdryer evenly over the affected area and a bit beyond. My heater is small enough to do the inside too. Then clamp a board over the humped-up area and let cool. Repeat until the top remains where you want it. You could dampen the exposed top in the bridge area and inside.
I would then fit a new bridge plate or add a lamination to the existing one, if not removed, it depends on the guitar. The grain of the plate I try to run at an angle. Many times I have found the need to add a brace to the top, along the back of the bridge plate. I would then cleanout under any loose braces and reglue them.
I do the same operation, in reverse, for the sunken area of the top in front of the bridge/soundhole area.
Don't forget to check the radius under the bridge itself, and correct if need be. It's not the full story but I'm sure you get the idea.
Good luck Taff
OK, sounds like you have nothing to lose from trying to flatten out that crinkly thing, and if that fails a re-top is not out of the question. Life in the old girl yet......
Thanks Mark. I'm pretty sure a re-top is way beyond my level of competence. I'd hate to give back a sad pile of wood.
Thank you, that's very helpful.
I clamped it overnight after applying moisture and a heat blanket to the bridge plate, and it is somewhat better but still quite bellied. I will do that again, add moisture to the top bridge area as you suggest, and heat the top in a larger area, perhaps with the heating pad I use for my own back as opposed to a hair dryer.
How do you clamp the sunken area? Do you make a caul for the inside that goes between the X braces, or a larger one with cutouts that go over the X braces? If you happen to have a picture of that it would be helpful.
Again, thank you. At least now I know it can, and has, been done.
Hi Again Elaine, here are a few photos from one of the jobs more recently. There are captions on the photos, but if not enough info let me know. This guitar was a Cole Clark, with a bracing system I have had to rework a few times.
The extra brace, in this instance, was used to strengthen the sunken area. I placed a bar across the top and pulled the face up to it with clamps. The brace I used to stiffen the one already in place, in this case, it was glued on top of the existing one.
The caul used to pull against would be as you suggested, whatever is best to apply even pressure from inside.
Thank you Taff, that is great!
I'd say nix on the bridge doctor, at least until you string it up and try it out. It took a ladder braced S S Stewart (with a big belly) from having a nice ring to now sounding like a thud. I'm just going to have to take the back off and x-brace it I guess.
Yes, I will string it up first. I'm on my third round of heating with moisture and clamping, and things are coming along slowly, with a bit of improvement each time.
I used the bridge doctor on a couple of other guitars, and it worked out nicely to correct the belly. I couldn't discern any degradation in the sound, but who knows. They didn't have the severe deformation that this current one has. I think the bolts allowed the bridge to stay on, tilt, and act like a lever to deform the top.
Thanks again for the advice.
I would replace/reglue both the bridge plate and the bridge to keep the top flat after heating to flat. Wood has a memory and will probably revert to the previous state after some time with strings at tension. Regluing the bridge and replacing the bridge plate will help a lot. Having the grain in the bridge plate going in the direction of the grain in a solid spruce top will give better resistance against deforming.