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A guitar that I built for a friend four years ago suffered some damage due to excessively low humidity this past winter. First, the top seam separated, which I repaired thanks to some great advice from Hesh. Upon closer inspection I found that the bridge was lifting up as well .

So, I heated it with a small silicone blanket to about 65 C (150 F) and gently pried it off with a putty knife by slowly working the knife under the bridge, but never pulling up on it. At least I thought I was being gentle. When I got the final corner off, I noticed that a sizable portion of the top (Engelmann spruce) came with that end of the bridge (see photo). The section is about 1 inch square and almost 1/32" thick at one corner. Two smaller sections are also at the opposite end.

My first question for the experts is: "What did I do wrong?".
I've used this technique before, with no problem at all.

My second question is: "What's the best way to repair the top?"

Thanks,
Chris

I'm no repair expert, but here's my two cents.

The way the fibers stop exactly at the edge, and the dark straight line where the chunk came up make me think you cut a little too deep with the exacto. The grain looks severed. It looks like you used a PVA glue. If it were me, I would carefully scrape the white glue off with a razor. I would leave the chunks in situ. I would put masking tape against the bridge pin holes inside to prevent glue squeeze out inside to prevent the caul from sticking. I would make a fresh but small batch of HHG. I would get everything set up, apply a liberal dose of HHG, and clamp the snot out of it.

I pretty much agree with meddlingfool on the repair.

You could heat the bridge up and try to remove the pieces intact but that will probably be a challenge. If you did that then you could glue the pieces back in like a puzzle and then sand it off smooth, clean up the bridge and reset the bridge but it could be risky trying to get those pieces off the bridge as one.

I don't really know what I am talking about since I am self learn't.... n' I an't got no book-learnin'

I am sure there will be an expert along shortly....

Cheers,
Bob

Step one is to repair the top so that you have a proper gluing surface for the bridge reglue.

Since you asked what may have gone wrong here's my thoughts: Removing a bridge with a pallet knife is how I would have gone about this one too. The idea though is to heat the bridge enough so that the glue layer between the bridge and top softens and gives way. The knife is used to work through the glue layer and part the pieces. You were correct to not attempt to pry anything apart instead using the knife to separate.

Mind you this only works well if the bridge is hot enough to soften the glue layer and the glue used is serviceable and will release at a civilized temperature like HHG and Titebond will - usually around 145F.

Your knife may not be "safed" enough or ideal for this from the looks of it. If you check out the Stew-Mac pallet knives including the new big mutha... that is excellent by the way you will see that things have been done to the business end so that they will not dig into either the bridge or the top.

So where we are now is it's likely that either your pallet knife technique was a bit off or the glue was not soft enough due to not enough heat when you started or both.

In addition runout plays an important role here. If you insert the knife against the direction of the runout which changes for both halves of the top mind you you can dig up the top. Before removing a bridge I sight the top from the neck end and attempt to get a handle on the runout direction and then if it is notable (which means that it can bite you if you ignore it) I usually make a mark on some masking tape on either side of the top pointing in the direction that I want to use the knife for each on side of the top. This is for the initial approach with the knife.

Using the runout direction in your favor can help lay lifted top fibers back down using the knife not in the direction of the runout can, of course, lift fibers.

A word about Engleman - IMHO Engleman does seem to peel apart more during bridge removals. Not as bad as WRC..... but one of the spruces that can come apart if everything is not perfect during a bridge removal.

I second Ed's remarks about the cuts into the top likely when clearing finish for the bridge glue-up. Looks like they were a little too deep....

Next how to repair the top. You could with an uber sharp chisel and slice the remaining top pieces off the bridge bottom and then using HHG and a flat board as a caul with waxed paper on it and a lot of clamping horsepower repair the top by reglueing these pieces. Next step would be to sand the bridge flat and clean and then scrape just prior to gluing.

Because of cuts though the top AND the idea that the bridge's trailing edge does the heavy lifting in preventing the bridge from lifting these cuts must be addressed in my view. Throw in the species as Engleman as well and I'm going to recommend Frank Ford's method of using a "scoop of top wood pieced into the top and glued, etc. This would take that cut edge on the bridge's back side out of play.

I'm pressed for time right now with a sick family member so I can't find the link at the moment to FRETS.net where Frank's toot is but if you want to post there the guys I am sure will help you out. They are a great bunch who are always willing to help and the advice is always very reliable IMHO.

If I can catch my breath later today I'll look for Frank's toot too and post it.

See, I told you an expert would be by shortly

Cheers,
Bob

I think a heat lamp does a better job of uniformly heating bridges for removal. (Protect the top from heat!)

I'll second Hesh's remarks about runout, and add that the side that appears lighter is the side with the grain running up. (Think about it this way: on one side, you're looking down the barrel of the wood pores, on the other, your looking at the sides of the fibers.)

That won't help you now.

Remove the top wood from the bridge using steam. A wet rag, and a good hot clothes iron will do the trick, and they'll come off easily. Fit these pieces in carefully when you glue them back.

I think you'll be okay structurally. Most of the tension comes in the center of the bridge, and the top there looks intact.

The front edge of the bridge in the center looks pretty chewed up. do a good clean scarf repair, or make a new bridge.

I think that Eric may be right that you could piece the damaged area back together and then with a flat board, caul with waxed paper on it firmly clamp the inlaid pieces in place. You will also want a caul inside the box too. You want to replace as much of the missing wood as you can.

There are no hard rules here but we like to see at least 85% of the original gluing area available AND it's also likely that you could gain some gluing area if the finish was not cut back all the way to the bridge peremeter although from the pics it looks like it was.

I'm still a bit concerned about the deep cuts through the top but think that perhaps simply replacing fibers may work too.

If not...... here is a link to Master Luthier Frank Ford's excellent toot detailing yet another approach.

http://www.frets.com/FretsPages/Luthier/Technique/Guitar/Structural/00028TopFail/00028top.html

Thanks for the help everyone. I agree that I was probably overzealous when I used an exacto knife around the perimeter of the tape I used to mask the bridge. Nor did I pay any attention to the run out when I removed the bridge last night. Live and learn.

I'll toss out one idea that I had for the repair. How does this sound?
At the worst spot, about 1/32" thick has been removed from the soundboard. What if I route out the entire portion of the soundboard to this depth, and then glue in a 1/32"+ thick patch? Or perhaps do this procedure to the worst section(s)? Sand/scrape flush, and then glue the bridge on top?

I am not sure what gain that would give you for this repair. If this was a guitar you got with no bridge or the wood was not stuck to the bridge then that would be a viable repair. I once repaired an old beater that had the wood ripped off right down to the bridge plate and I repaired it with the method you are talking about but this really isn't that severe. You have the pieces and the way it is ripped off will actually give you more gluing surface because of the jagged break. As long as you don't disturb the mating surfaces they will sort of lock into place.

So I think the above answers are your best and easiest way to fix this. I agree that you may want to make a new bridge that is just slightly oversize to cover the edges.

Again.... I am sure the pro's will have a much better answer than I do.

Cheers,
Bob

I would use a very sharp wide enough chisel and remove the spruce off the bridge with one stroke trying to take it right down the glue line erring on the side of removing wood from the bridge, your gonna have to sand that flat anyway. Then use the clamping method described above to get it flat and tight. Personally I think it would be a bit more risky to just glue it down as is though it would probably work as well.

Done right and it will last.

I wouldn't.

I frequently repair classical guitars that have had the bridge fly off under string tension. The pictures in this case are pretty typical. (Nylon strings have much lower tension, but the pin-less bridges that are typical mean that failures are more dramatic.)

The repair I've suggested is one that I have plenty of experience with.

I see no advantage to removing the chips from the bridge. They're already exactly where they need to be. Well, on one side anyway. If you can get the old glue off in the middle (which, by the way, looks like it was not clamped fully in the first place), you could just pop it back in place. This is exactly why I have switched to HHG for bridges, as you don't need to remove old glue but just reactivate it...

I still would clean up the bridge to have a perfectly clean, freshly scraped surface prepared for new glue. Even though a chunk remains attached as Ed says how much do we really trust the original glue-up - after all this bridge did decide to come off... So why not start fresh and new.

I often chisel off larger fibers if and when that's already what's handed to me and part of the lifting bridge meaning the damage is already there. Our bridge removal method(s) never takes this much wood with it.

What's helpful to me when chiseling off some fibers from a bridge bottom and when I may want to return these fibers to their original locations on the top is to use a VERY sharp chisel with a bit of a slicing action and not a pushing action. It's also a great way to remove the excess from plugs that we might turn on our lathe for filling previous tuner screw holes that are no longer needed after a tuner swap. The slicing action is a bit safer in my view too because the tendency to apply much pressure won't get you where you want to go with instead the slicing action progressively slicing through the glue layer. There is a boundary layer there too but let's not go there for now it will make my head hurt...

Be very sure to remove all of the old glue residue from the rest of the bridge patch on the top too. It can look like it's gone when it's not really gone.

One more thing - why did it lift is a question that may have important bearing on how well it stays in place going forward. So I would reexamine my fitting methods and my clamping methods as well as perhaps any specific requirements of the intended glue that you want to use.

If that were me, I would try to reglue the missing pieces in, back where they came from, then amek a new and wider bridge. The broken end grain fibers wont have much strength in them, no matter what glue you use .. I would want to be gluing onto uncut strong fibers,not back onto the ones that gave way ... I route the finish off in order to glue my bridges down (after scoring very lightly, only thru the tape that has the bridge outline on it - there is a mark in the finish, but not thru it at all, I use a mini die grinder setup and 1/8 inch bit) .. no cut fibers at all this way

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Thanks for the help, everyone. I'll keep mulling this over. The consensus seems to be to reuse the spruce that pulled off the top rather than fitting in a freshly prepared patch. Shows how much I know...

For what it's worth, the bridge was originally glued using LMI white glue using the fixture below. Obviously there is a caul under the bridge plate. Assembling this was a pain, so I've switched to standard deep-throated C-claps on my latest builds.

I recall that there was ample squeeze out because I felt that I did a poor job cleaning it up! I do believe the primary culprit was this winter's low humidity. The center seam of this guitar's top separated, and the same person's Martin suffered a top crack at exactly the same time. I had checked the guitar out just a couple of months earlier (she lives just up the road from me), and saw no evidence of the bridge lifting then. Slicing through the top with my Exacto knife was just stupidity on my part and is the reason large sections of spruce came off with the bridge.

For what it is worth, I never slice the finish to remove it where the bridge sits. What I do is position the bridge in its location then run blue painters tape right up to the edge all the way around it. Then I remove the bridge and put about 3 more layers directly on top of the original tape. That aids in positioning the bridge when I am ready to glue it down. I then use a 1/2" chisel blade X-acto knife to scrape the finish off just leaving about 1/32" up to the tape line. Then I scrape the very edge of the bottom of the bridge at a slight angle to accommodate the 1/32" of finish that I left just before the edge of the tape. When I am ready to glue the bridge down the 3 or 4 layers of tape give me a positive channel that the bridge fits into so I know it is right where I want it. I use the Stew Mac bridge clamps which I have found to be really nice since they are small and very light but quite strong. I have a couple of other types of clamps I have bought over the years but I now only use the Stew Mac ones because they are easy to position with the 3rd screw/foot. However I have thought about getting the type you are using. It looks really easy and would have no worries of scraping the top.

In the past I always sliced the finish before removing the finish but I have had chips that extend out past the bridge or have the slice visible after I glued the bridge down. By using the method I use now I get a really clean bridge install. Besides I was always worried about slicing into the top.

Cheers,
Bob