Redwood top failure?

[Bob Gramann]

This is the first time I have tried a redwood top. The instrument sounds great and is wonderful to play. But, for the first time in my building career, the top has separated from a brace (below the bridge on the bass side) causing a large and growing belly on the tail side of the bridge. In an effort to understand this, I took an offcut from the top and glued a brace piece to it (HHG as always). The photo shows the result with only mild finger pressure against the joint. Assuming that this is what happened inside the guitar, I fear that I am going to have to retop this guitar. Has anyone seen this before with redwood? And, did you find a successful remedy?

[Mark Swanson]

I have heard of such things happening before and I know luthiers who have sworn off redwood for just that reason. But myself, I have built with the stuff I have and after about 15 instruments have never seen any failure or problem. There is a lot of variation in redwood, and I think that might be the reason here. The stuff I have is quite flamed and many people swear that it's dumb to build with the flamed redwood because it has so much runout that disaster is sure to result, but I have built quite a few instruments with it and have no sign of failure.
So let me make a guess. Could it be that a top with very little runout- it looks like your top has very little, at least compared to my flamed stuff- can "peel" apart much more easily than a flamed one, since the grain changes so fast through the flamed area. Maybe the glue can grab the alternating grain and make a stronger joint? And maybe the alternating grain resists that peeling effect a bit better? Just my guesses!
I might as well post a discussion and show you my redwood guitar...good luck Bob!

[Bob Gramann]

The top I have is as close to perfect as a top can be (except that it is awfully soft). There's no flame or detectable runout. It sounds like I'm going to have to replace the top.

[Alan Carruth]

Bob Gramann wrote:
"The photo shows the result with only mild finger pressure against the joint. "

Finger pressure in what direction? Redwood splits easily, and sideways pressure could well have started it peeling loose.

I note that you had 100% wood shear, so there was no problem with the glue joint. Sometimes redwood can have 'low surface energy', and acts almost as if it were lightly waxed, making it problematic to get good glue joints. The remedy there is to glue it as soon after working it, or work it just before gluing, and then keep the clamps on until the glue is really dry.

I also note that you've got a nice big footprint on the bridge, which is the only way to keep one down on redwood. The low peeling resistance means you have to keep the max stress low on any redwood construction. It's possible that a wider brace would have done the trick. Then again, maybe not.

Alan Carruth / Luthier

[Chris Reed]

Would it be any use trying CA to reattach the brace? It seems to penetrate a little way into the wood, which might help stop this peeling. If the brace is only separated in places, running some CA into the gap and clamping can be done without removing the top. I've fixed a loose section of uke bracing like this.

But that's my only experience, and non-redwood at that. On the other hand, if the only alternative is re-topping it can't make things worse to try it.

[Bob Gramann]

It hurts to learn about that low peeling resistance this way. This one sounded so nice that I ordered another piece of redwood before the brace peeled off. In my test, the finger pressure was lifting the brace from the redwood. The redwood scrap was from the part immediately adjacent to the brace that lifted so it's easy for me to speculate that what I see is what happened inside the guitar. If I do use that second redwood top, I will use wider than normal braces. But, I might not risk another one.

I never use CA for structural joints. I've seen it fail over time too often. I would have little trouble regluing it with HHG in place but, I'm unwilling to put a potential time bomb into a customer's hands. I don't like my instruments to come back.

[Chuck Tweedy]

I think there is just a huge variation in redwood.
I have a guitar I made - very similar in size/shape to the one you show - and it has a redwood top that appears very similar (grain width & color).
However, it has super-narrow braces (~3/16"), and a small footprint bridge (15/16" x 6") - and shows no sign of peeling.
As a matter of fact, I intended to use extra-lights on it, but have moved up to lights with no distortion (or damage) and better sound. And it's been stable for much more tan a year.

[Bob Gramann]

I tried my brace experiment on the new redwood top that I recently received . The brace peeled off easily with hand pressure just like the first piece. When I re-top, I don't think I'll use redwood. Darn. It sounded really nice.

[Nick Dingle]

Dang, now I'm worried about my last one. Redwood top, very similar in appearance to yours. I'm not game to reach in and see if I can yank a brace off

Don't know what if any difference it makes, but mine was reclaimed timber, and my be a fair age....

[Bob Gramann]

Nice looking guitar. I hope that I just got a couple of weak pieces and that yours isn't at risk.

[Clay Schaeffer]

One reason to make redwood and cedar tops a bit thicker is to give them more stiffness in the plate. This might reduce the "peeling" forces that the braces have to resist. It would be interesting to see what the Engineers could calculate in this regard. And while they are at it maybe a quantitative analysis of what increasing the brace footprint will do. <g>

[Bryan Bear]

I am far from an engineer, but as I was reading the first part of Mark’s post I was thinking that in this case the reversing localized runout of a curly top might effectively reduce the peeling problem (though increase the risk of a fracture). It was interesting to then read Mark speculate the same thing. Any engineer types want to weigh in?

[Alan Carruth]

I think the only ways to reduce the peeling stress on the back edge of the bridge are to make the bridge wider and to lower the string height off the top.

Redwood seems to be even more variable than most top woods, and it's often hard to tell whether you've got a good piece or not until you've glued it up. I got a bunch of redwood once that came from a planter manufacturer that went out of business. The pieces were all about 24" long and 8" wide by 1/2" thick or so, just big enough to resaw into a top, and they only cost fifty cents each. My wife and I spent an hour or more going through the pallets of wood in the surplus store looking for the quartered pieces and tapping them to cull the best ones, and some of them were really nice. Some of them made great guitars, and some of them split sitting on the shelf. Overall they were a good buy, but the wastage was fairly high.

Alan Carruth / Luthier

[Bob Hammond]

My two cent contribution is that redwood tops might need a different bracing strategy. The fitting of the pieces was good and 'pro forma', and the glue did not fail. It appears that the redwood tore apart. Maybe the braces should be angled nearer to the axis of the grain direction. Maybe they should have a broader footprint, or maybe there should be more braces.

[Andrew Porter]

How about using a thin sheet of something, even paper over the the inside of the top surface to distribute the stress? Perhaps just in the region of the braces.

[Dick (DT) Trottier]

I'd read about something similar in a recent GAL magazine, braces separating from the top on plywood basses. The fix was to increase the gluing area by applying a fabric patch over the brace that extended some distance over the plate. Fabric was linen coated with hide glue stippled tight to the wood with a small paint brush.
Good luck...

[Ron Daves]

When I was building a guitar with rosewood in it, the instructions I was following said to "leach" the glue area with acetone to get rid of the oils present in this species.

So, when you put on the new top, how are you going to get the fretboard and the old top off? Did you use Hide Glue on it?

[Mark Swanson]

You don't have to be gentle when removing a bad top. You can saw it off with a handheld jigsaw if you want, doesn't much matter if it's trash! the fingerboard comes off with a little heat.
The talk about using acetone on rosewood comes up here every so often. We have pretty much proven that it isn't true and actually doing so will hurt the glue adhesion. All you need to do is glue to a freshly prepared surface, sanded but scraped is better yet.

[Bob Gramann]

The top is entirely constructed and attached with hide glue. The fingerboard tongue is attached to the top with Titebond (but with HHG to the neck) so it will come off easily with heat. I will rout off the binding (persimmon), put the body back in the external mold, stick a think blade between the top and the side, and zip it off. Given my experiments with the redwood, I don't expect a lot of resistance. I haven't decided if I will try to save the persimmon bridge or just make another. I will probably give it a knock and see if it releases easily. It's held on with HHG. All of this will wait until I get the current batch of instruments to a good stopping point.

[Michael Lewis]

Bob, before trashing the top why not try the suggestion of gluing it with CA? You don't have anything to lose at this point and could save a lot of work if it works. Tom Ribbecke made several flat top guitars with CA many years ago and the last time I talked with him they were still out there in the world and none had come back to him. It may not be the best choice for general construction in most cases but in this case it seems it might save the day.

One point regarding CA on very porous wood is the very thin stuff soaks in quicker than it cures. I would leave the hide glue where it is since it is holding wood fibers, and flood the effected joints with thin CA and let it soak and cure. I think it should harden the surrounding material where it soaks in, just like it does when you spill it on the top before finishing starts. Probably it won't soak through the top to show on the outside but one never knows until it either does or doesn't.