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How to unglue cold glue?


tango
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I have often been able to undo things glued (with unmentionable glues) with water and patience.  Water does not dissolve white or yellow glues, but it does soften them.

Brush some water on the glue and keep it wet.  If you are dealing with the type of glue that this works on, after 5 to 10 minutes the glue will turn from translucent to an opaque white or yellow, and it will begin to soften.  As it softens, scrape it off, but don't scrape off any wood.  Scraping off softened glue will uncover unsoftened glue underneath.  Keep wetting the glue and scraping it off as it softens.

If you are dealing with a crack in a top, remove the top before starting.  This will enable you to work on both sides at once.

You may reach a point where you cannot get out any more glue because it's inaccessible in the crack.  Try digging the softened glue out of the crack with finely pointed metal pick.  Keep wetting the glue and flexing the crack.  Try driving a very thin blade through the glue then running it along the length of the crack.

With luck, the crack will eventually open.  When it is open, continue wetting, flexing and scraping to get all the glue out of the crack.

Some people on this forum recommend vinegar, but I have never tried it.

People who use white/yellow glue on violins are usually incompetent in ways that can often work in our favor.  The repairs are usually poorly done, with cracks glued out of alignment and using an excess of glue.  These faults make it easier to undo the bad repairs.

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22 hours ago, Michael Richwine said:

Heat will undo just about all the plastic glues...

Yes.

So, what is a good heat source?  One that is convenient to use, that does not risk scorching the wood or varnish, that can be concentrated where it is need, and that does not dry out the moisture that also helps open the crack/joint?  It seems to me that a little steam nozzle would be best.  So, what is a convenient way to rig a little steam nozzle?

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I made a steam generator out of an old "instant pot" from a thrift shop, some hydraulic line, some small diameter brass tubing and a homemade handpiece. You have to let it warm up thoroughly, and it still drips a lot, but it's handy for getting moist heat where needed. Still, for other purposes, a household iron on low heat works pretty well if you are careful around the  varnish.

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Carefully applied hot water can often loosen wood glue. I’ve used vinegar in some cases, but I often find that Laponite will do a lot to soften the glue from the outside of the crack and Triton will do a good job of penetrating into the crack so I can remove the glue. When the glue softens enough to be rubbery, I can gently lift it out with a very fine dental pick without harming the wood.

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4 hours ago, The Violin Beautiful said:

Carefully applied hot water can often loosen wood glue…

I don’t think so, because hot water applied carefully, as with a brush, cools off too quickly for the heat to accomplish anything more the room temperature water would.  In order for hot water to retain heat long enough for the heat to be helpful, the crack (or whatever) would need to be flooded with an amount of water that would be tantamount to immersion.

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1 hour ago, Brad Dorsey said:

I don’t think so, because hot water applied carefully, as with a brush, cools off too quickly for the heat to accomplish anything more the room temperature water would.  In order for hot water to retain heat long enough for the heat to be helpful, the crack (or whatever) would need to be flooded with an amount of water that would be tantamount to immersion.

Sous vide violin? I'll take mine medium-rare.

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3 hours ago, Brad Dorsey said:

I don’t think so, because hot water applied carefully, as with a brush, cools off too quickly for the heat to accomplish anything more the room temperature water would.  In order for hot water to retain heat long enough for the heat to be helpful, the crack (or whatever) would need to be flooded with an amount of water that would be tantamount to immersion.

You have to keep refreshing the brush with hot water and removing cooled water with a paper towel, but I’ve done it on many occasions. It doesn’t work on all wood glues, but it’s an easy method to try.

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Guitar repairers remove necks glued with Titebond with steam. I made a system from a cheap used espresso machine; clamped a thick (natural gas) hose on the steamer spout with a tube clamp, and one of those pump needles for pumping air into balls on the other end, also clamped. You must use gloves with this, even the hose gets really hot!

I have never used this system on a violin or even a bass, and would be VERY wary, as steam may damage varnish and undo other glue joints. But perhaps with a removed top, this could be used to direct steam on the inside surface of a crack glued with white glue. On a violin of little value ;)

Otherwise I support Brad Dorsey's description: water, patience, scrape... very slow and frustrating, but what can you do (besides curse the idiot who did it...)

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