Bridge lifting on cedar top

Fatfinger McGee · #1 01-29-2021, 01:34 PM

I have a fairly new cedar-topped guitar, and the bridge has suddenly begun lifting. Looks like a simple glue failure. A quick google search suggested cedar is more prone to glue failure thanks to the oils in the wood, which I guess I can vouch for.

My trusty luthier stopped taking repairs last fall, due to a spike in demand for his guitars (thanks COVID!). Before I take it to a new one, is there anything special they should know about gluing to cedar tops? Titebond and hope for the best?

Bill Kraus · #2 01-29-2021, 06:05 PM

There is a chance that if light clamping pressure holds the bridge down, some glue may be worked under the lifted portion and the bridge can be re clamped. In some cases the bridge should be removed completely and re glued. Many factories use a Tightbond type glue, and some luthiers may use hide glue. If the repair person is going to work glue under the lifted portion of the bridge, they would obviously want to confirm what kind of glue the manufacturer used originally.

redir · #3 01-29-2021, 07:33 PM

IT could be a worse problem then just that. A popular technique for gluing qa bridge down on a new guitar is to finish the entire guitar first and buff it out, then place the bridge. They might use an Exacto blade or some such thing to score a line around the bridge to mark out it's location and then remove the finish under the bridge footprint. What ever technique a builder or a factory does to do this can scratch too deep on a cedar top, and it doesn't take much, and cause this problem. Cedar has a tendency to peel away from itself under those conditions.

So for a cedar top guitar with this problem I would definitely remove the bridge to have a better look at what is going on. In fact on any guitar 99% of the time I would probably remove the bridge.

mtdmind · #4 01-29-2021, 08:14 PM

Are you handy with tools? I am not, but I reglued my Guild and it was not too hard to do. Watched lots of youtube videos showing how to do it. Cost me $20 for some tools. Guitar plays awesome since.

rick-slo · #5 01-29-2021, 08:46 PM

Some cedar wood fibers of the top are more likely to peel right off with the bridge when it is removed, so extra care. They probably already know that anyway.

Fatfinger McGee · #6 01-30-2021, 07:42 AM

Quote:

Originally Posted by mtdmind

Are you handy with tools? I am not, but I reglued my Guild and it was not too hard to do. Watched lots of youtube videos showing how to do it. Cost me $20 for some tools. Guitar plays awesome since.

I am pretty handy, and have both Titebond and clamps that should work. But it’s due for a setup, worth it to have someone who knows what they’re doing take care of it.

Thanks for all the advice. I think I’ve found a good local tech who said all the right things and is well recommended, so all set.

Alan Carruth · #7 01-30-2021, 11:19 AM

New Titebond doesn't stick to old Titebond as well as it does to a fresh wood surface. Simply working some glue in under a bridge that is lifting will result in a bond that's less strong than the original, which was not strong enough to being with. You really have to remove the bridge and clean off all of the old glue unless it was done with hot hide glue originally, and that's what you're using for the replacement.

The problem with WRC is not one of 'oils' in the wood, it's a matter of 'surface energy'. When you remove material from a surface by cutting or sanding it you're actually breaking chemical bonds. These can remain 'open' for a while as they find things in the air or on the surface to latch onto. If you put some glue down during that period the wood will latch onto that, and you get a stronger bond. Work done in WW 2 in the Forest Product Lab showed that you would get significantly stronger bonds if the wood was glued up within fifteen minutes of being worked.

You can test the surface energy of a piece by spritzing it with a light mist of water. If there are open bond sites the polar molecules of the water will be attracted to the slight charges produced, and it will spread out into a thin film. If the surface energy is low the water will bead up, and they actually measure the surface energy by taking photos and looking at the angle the edge of the drop makes with respect to the surface.

Some materials naturally have lower surface energy to begin with for whatever reason. I imagine there are also differences in how fast the surfaces of different materials react. It FPL probably used spruce in their experiments, since they were looking at aircraft structures; cedar may react faster.

I know this is a problem with redwood. When I made my first redwood top in a class I planed the joint to fit, but did not glue it until a week later, iirc: the clamping press was occupied. The top simply fell apart along the glue line when I took it out of the clamps, and I had to re-do it. The teacher said he'd seen that before, but we did not know what the problem was at the time.

StrumChi · #8 03-16-2021, 07:54 PM

Do you have a picture of it? Believe it or not removing and re gluing bridges are some or the first guitar repairs I did. Easier than it sounds. You can find videos all over YouTube, but here is the cliff note version. Heat up spatula, and slowly work it under bridge, cutting through the glue. Keep reheating it. Scrape off all the old glue. Maybe put the bridge under a belt sander to remove the old glue. You need three clamps do it right. I believe they need to have a 6" depth. Regular titebond works great and is easy to work with. I leave the clamps on for 24 hours, but I've read only an hour should suffice.