Tough bridge removal -- what glue was it?

Construction and repair of Classical Guitar and related instruments
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Chris Sobel
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Tough bridge removal -- what glue was it?

Post by Chris Sobel » Fri Feb 19, 2016 3:50 am

I removed a bridge today that was pretty rough to get off. It's from the 60's Di Giorgio that I posted about elsewhere. The bridge was likely repaired before and had lifted from the rear a good bit by the time I got to it. Finger pressure from either side wouldn't close up the lifted portion so I decided to pull it... I've not had a bridge removal experience like it… It was completely resistant to all heat. Portions of the bridge (the wings in particular) came off ok with moisture, and it smelled a little like fish glue. Other portions of the bridge would simply not come off with either water or heat, or any combination in generous amounts.

Any thoughts on what glues may have been involved? Some of the glue smelled like fish glue for sure, but I'm wondering if there was a repair done with epoxy or something? It definitely took some chunks of top with it when I finally got it off.

Chris
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waikuentsui
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Re: Tough bridge removal -- what glue was it?

Post by waikuentsui » Fri Feb 19, 2016 5:10 am

Chris,

I had a similar experience.
The lifted bridge was repaired by the previous owner, who not only put glue on but also put two bolts on the bridge.
The guitar sound nice the way it was. I just did not like the look.

I did not think it would be such a hard job.
I have removed bridges before. Usually just a bit of plying plus heat (if needed), the bridge will pop off.
In this case, the bridge will not give.
I heated the knife first. When that did not work, I heated the bridge as well.
In the end, it was just brute force that made it came off.
The bridge took a fair bit of wood off the sound board when it finally disengaged.
bridge with bolts.JPG
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Michael.N.
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Re: Tough bridge removal -- what glue was it?

Post by Michael.N. » Fri Feb 19, 2016 8:36 am

Powdered resin glue (sometimes called the boat builders glue) is impervious to both water and heat. It dries glass hard. Romanillos used it to glue his bridges in the belief that such a joint should be permanent or that other glues weren't quite up to the task.
The epoxy that I've used does release with heat but I can't remember how much heat it takes. Sometimes if bridge removal is so difficult it's better to plane the bridge off, save the top wood. If you want to save the bridge, it can be a real struggle. It's why the use of reversible glues on instruments are important.
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Alan Clark
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Re: Tough bridge removal -- what glue was it?

Post by Alan Clark » Fri Feb 19, 2016 11:01 am

The epoxy glue that I am familiar with here in the UK is Araldite, slow setting. As an archer who makes his own wooden arrows I use it to glue on the metal points. It is reversible, with heat. If I break an arrow and want to re-use the point, I hold the point in a candle flame. After a few seconds the glue goes soft and the point can be pulled off with pliers.
Obviously you can't do this with a guitar bridge! But maybe you could use a cobbler's knife with a flexible blade, insert it under the bridge, and heat up the blade. How did you apply heat Chris?
Maybe the bridge repair was done with epoxy, and it softened a bit when heat was applied. Or maybe it was repaired with Gorilla Glue or some other brand of expanding PU foam adhesive. I also use this to glue on arrow points, and it breaks down when heated up.

Interesting that Romanillios used powdered resin glue for gluing bridges. When I was a professional lute maker I used it (Cascamite) to glue a lot of bridges on, and never had any problems with it. But that was a long time ago. They changed it, I believe, and it is now called Polymite. Not sure if it 's as good as it used to be.

Alan

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Michael.N.
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Re: Tough bridge removal -- what glue was it?

Post by Michael.N. » Fri Feb 19, 2016 11:23 am

I used Cascamite for gluing purfling to bindings and for gluing veneers together for rosette mosaics. It has a long open time and can take extreme heat without the glue letting go. There is no known solvent for it. Ultimately hide glue is easier to prepare, easier to clean up and more pleasant to use. I haven't used Cascamite for many years. It's use should be pretty limited, certainly in finely made guitars that may well need to be repaired at some point.
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Re: Tough bridge removal -- what glue was it?

Post by Imbler » Fri Feb 19, 2016 2:50 pm

You could try touching the left behind glue with a damp finger. If it is fish glue, it will feel tacky to your finger,
Mike

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Chris Sobel
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Re: Tough bridge removal -- what glue was it?

Post by Chris Sobel » Fri Feb 19, 2016 4:11 pm

Alan Clark wrote:The epoxy glue that I am familiar with here in the UK is Araldite, slow setting. As an archer who makes his own wooden arrows I use it to glue on the metal points. It is reversible, with heat. If I break an arrow and want to re-use the point, I hold the point in a candle flame. After a few seconds the glue goes soft and the point can be pulled off with pliers.
Obviously you can't do this with a guitar bridge! But maybe you could use a cobbler's knife with a flexible blade, insert it under the bridge, and heat up the blade. How did you apply heat Chris?
Maybe the bridge repair was done with epoxy, and it softened a bit when heat was applied. Or maybe it was repaired with Gorilla Glue or some other brand of expanding PU foam adhesive. I also use this to glue on arrow points, and it breaks down when heated up.

Interesting that Romanillios used powdered resin glue for gluing bridges. When I was a professional lute maker I used it (Cascamite) to glue a lot of bridges on, and never had any problems with it. But that was a long time ago. They changed it, I believe, and it is now called Polymite. Not sure if it 's as good as it used to be.

Alan
Alan,

That's exactly what I did... I have a heat blanket with thermocouples which I use for repairs. At first I heated the tie block area and let the heat sink in. When that didn't do anything I worked the spatula in a applied heat to it, to no avail.

I knew at the very least I was going to have to pull the back to replace a mangled centre brace and quite a few large cracks/seam separation etc. The bridge had to come off to do a good job fixing the separation given that it wouldn't close back up, IMO. All this has made me decide to re top it.

Chris
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Alan Clark
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Re: Tough bridge removal -- what glue was it?

Post by Alan Clark » Fri Feb 19, 2016 5:15 pm

Sounds like you have quite a job on there....
Hope it goes well.

Alan

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Re: Tough bridge removal -- what glue was it?

Post by MessyTendon » Fri Feb 19, 2016 7:07 pm

Sounds good, hopefully the client will be happy too. One more possibility, you might need a solvent to break the bond. If you knew what it was that would be a lot easier. But a solvent should break it down. I would try the solvent, then you could open the back but avoid a re-top. With small drops in a pipette or small syringe you could put little drops on and see what happens, a sharp thin knife to break the bond.

I just hate seeing a good top go to waste. But if it's necessary that's just the way the cookie crumbles.

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Re: Tough bridge removal -- what glue was it?

Post by Steve Ganz » Fri Feb 19, 2016 11:44 pm

For the future. A more conservative approach (which you might have considered): Remove the bridge by planing it down to 1 mm or less, then heating and/or scraping. I wish I had done this on my first bridge removal.... It is tempting to try to remove and save parts such as bridges and fingerboards, but the substrate usually suffers.
Steve

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Re: Tough bridge removal -- what glue was it?

Post by chiral3 » Fri Feb 19, 2016 11:50 pm

Shocked an old-timer didn't chime in and tell you to grow a set and hit it hard with a hammer. :-)
Whatever catastrophe or dynamic equilibrium this will eventually lead to will be a mathematical not a moral phenomenon. - A Fryer

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Re: Tough bridge removal -- what glue was it?

Post by Dan Davis » Sat Feb 20, 2016 12:15 am

chiral3 wrote:Shocked an old-timer didn't chime in and tell you to grow a set and hit it hard with a hammer. :-)
"It'll pop right off!"
All of us contain Music & Truth, but most of us can't get it out. -- Mark Twain

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Chris Sobel
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Re: Tough bridge removal -- what glue was it?

Post by Chris Sobel » Sat Feb 20, 2016 4:18 am

Steve Ganz wrote:For the future. A more conservative approach (which you might have considered): Remove the bridge by planing it down to 1 mm or less, then heating and/or scraping. I wish I had done this on my first bridge removal.... It is tempting to try to remove and save parts such as bridges and fingerboards, but the substrate usually suffers.
Steve,

I actually did not consider this. I had it in my mind to reuse the bridge, but good riddance anyway… it weighed over 30g. I'll keep that in mind for my next bridge removal; makes a lot of sense.

Thanks,

Chris
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Steve Ganz
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Re: Tough bridge removal -- what glue was it?

Post by Steve Ganz » Sat Feb 20, 2016 6:48 am

30 g.
Excluding the carraige bolts I presume.
Steve

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Chris Sobel
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Re: Tough bridge removal -- what glue was it?

Post by Chris Sobel » Sat Feb 20, 2016 7:57 am

Steve Ganz wrote:30 g.
Excluding the carraige bolts I presume.
Oh sorry I was referring to just one of the wings of the bridge... Minus carriage bolt :lol:
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