# Am I going to bust a glue myth?



## DrRobert (Apr 27, 2015)

In another thread about re-glueing a split top, I made a comment that suggested dried glue will not interfere with regluing the joint. Others disagreed, and although I 'believe' I am right, I would rather know if I am wrong.

I know once I did end grain sizing on a miter joint, and waited too long, letting the glue dry, and thinking "this will never work", but it did..I think.....but my memory is very faulty. 

So, in the spirit of Patrick Sullivan (but not nearly the scientific approach) I thought it's a pretty easy thing to confirm or dispel. And please, please understand I am not doing this to prove any one right or wrong, I'm just curious if an assumption I made is actually true.

I realize applying to the post on the dresser top might be inconclusive, as there are no long term stresses to see if the bond weakens over time. I know this isn't totally scientific, but I think it will at least confirm 1) glue does stick to dried glue and 2) how strong is the bond? 

I applied an even layer of TB2 to these sticks and allowed them to dry, then applied another layer of glue & clamped using moderate pressure. 

For the test I'm going to clamp one stick in a vise and use pliers to try and pry the joint apart. If it holds, I'll whack it with a hammer. I'll post a video of the result after curing 48 hrs.


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## Rebelwork (Jan 15, 2012)

Some double glue mdf. 

So was the point others making that glue wouldn't stick to itself?


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## woodnthings (Jan 24, 2009)

Dr. Robert,
That's a different situation in your test. The desk top is old glue of unknown origin. Your test was new glue to new glue of a similiar brand, a different animal, in my opinion. I wouldn't base my decision on repairing the desktop split and warp based on this test, but the OP is free to make his own choice, of course. I would want a new, clean, uniformly square surface for my repairs. YMMV?

This video is about furniture repair and features my favorite restoration expert, Thomas Johnson:


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## epicfail48 (Mar 27, 2014)

Wood glues will stick to a pretty wide variety of surfaces that people say you shouldn't glue, they just don't stick particularly well. That's why people recommend against re-gluing old joints, it's a very weak bond. It'll hold, but not in the same wall that a glue joint in virgin wood does

I'm interested to see the results, but one thing I can see interfering with results is how long you let the first layer of glue sit before flying again. If the first layer didn't fully cure, you could still get some crosslinking between the 2 layers of glue like you would with coats of polyurethane, and that condition wouldn't actually represent what would happen if you redid an old joint


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## Steve Neul (Sep 2, 2011)

DrRobert said:


> In another thread about re-glueing a split top, I made a comment that suggested dried glue will not interfere with regluing the joint. Others disagreed, and although I 'believe' I am right, I would rather know if I am wrong.
> 
> I know once I did end grain sizing on a miter joint, and waited too long, letting the glue dry, and thinking "this will never work", but it did..I think.....but my memory is very faulty.
> 
> ...


It will work to glue together a joint that has already been glued however a year or two later it's likely to come back apart. If though the joint were brought back to raw wood the joint would last for decades. Then the type glue used would make a big difference. Hide glue or epoxy would hold such a joint better. I used to have a antique repair shop and did reglue some joints by working glue into the joint and clamp but those repairs usually came back. If you do very much warranty work you soon quit doing some things.


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## DrRobert (Apr 27, 2015)

I understand what you’re saying but:

Wood glue does stick to dry wood glue.

I know it all depends on variables like how much glue you can get in the crack, how much stress the joint is under etc.

For how long I don’t know but I don’t think the bond is coming apart anytime soon. I’m going to try this with hide glue and see if there’s a difference. I’ll give it a few more days to cure than the TB2.

@Steve the failures were probably more a function of enough glue coverage than adhesion don’t you think? I’ve seen Thomas Johnson work glue into cracks, even watering it down many, many times.


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## woodnthings (Jan 24, 2009)

I've seen that also, but most of the time when he's repairing a split or an old seam he uses hide glue, and according to him, it does work for that type of application.
His reasoning is that the old antiques used hide glue so it will be not only period correct, but if future repairs are needed, it can be heated up and released:


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## Steve Neul (Sep 2, 2011)

DrRobert said:


> I understand what you’re saying but:
> 
> Wood glue does stick to dry wood glue.
> 
> ...


When I worked glue into a cracked top I put a bead of glue over the crack and rubbed it into the crack with my thumb until glue came out the other side. I doubt if there was very much of it that didn't get glue. Many of the customers I had wanted the cheapest fix I could do. They were antique dealers that were wanting furniture repaired to sell it. Some of it came back before they could make the sale. Quite possible some of the repairs broke after the sale and I never heard about it. Anyway, I wouldn't charge anyone for making the same repair twice so I just quit repairing them without taking the joint apart and milling the edges. During that period I also reglued some chairs with wood glue. and had the same results. I then started regluing joints like that with epoxy and they stayed fixed.


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## GeorgeC (Jul 30, 2008)

woodnthings said:


> Dr. Robert,
> That's a different situation in your test. The desk top is old glue of unknown origin. Your test was new glue to new glue of a similiar brand, a different animal, in my opinion. I wouldn't base my decision on repairing the desktop split and warp based on this test, but the OP is free to make his own choice, of course. I would want a new, clean, uniformly square surface for my repairs. YMMV?
> 
> This video is about furniture repair and features my favorite restoration expert, Thomas Johnson:


I agree. Not as the old saying goes "apples to apples." I have no idea of what kind of test could be made that would make me believe in it.

George


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## Rebelwork (Jan 15, 2012)

Are we saying the new glue is fusing to the old?


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## DrRobert (Apr 27, 2015)

Rebelwork said:


> Are we saying the new glue is fusing to the old?


That was the main point I was trying to show.

The myth being glue doesn’t bond to dried glue residue.


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## Rebelwork (Jan 15, 2012)

I would think this information would be on the manufactures website..

Normally you want fresh wood so when glue is applied is absorbs into the fibers, grain or pores..


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## DrRobert (Apr 27, 2015)

That’s what I’ve always thought, too.
I think all I’ve proven is it will stick and stick pretty darn well.

How the bond stands up over time is another question.

I know wood glue can be reactivated with heat. I’ve veneered quite a few thing using dry glue/hot iron technique.


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## Rebelwork (Jan 15, 2012)

Considering all glue manufactures are looking for an edge, I think if it was a fact it would be on their website. I haven't looked ...


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## DrRobert (Apr 27, 2015)

Interesting I just read a thread with the identical problem over on the FWW forum. 6 out of 7 responders said use a wedge & work glue in the crack.

A shop vac to suck it in, dental floss, and blowing glue through a straw.


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## AwesomeOpossum74 (Jan 27, 2017)

DrRobert said:


> A shop vac to suck it in, dental floss, and blowing glue through a straw.


A small vacuum can do a great job pulling glue through. Doesn't need to be powerful, just targeted on a small area at a time.


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## woodnthings (Jan 24, 2009)

Thomas Johnson always uses a small syringe for applying his hyde glue onto a seam, way less mess to clean up. 
NO vacuum hose to wash the glue out of .....


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## redeared (Feb 7, 2019)

Hide glue is much more fluid than PVA enabling it to get into cracks easier


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