Reversing Hide Glue

B

briyon

Well-known member
I am relatively new at using hide glue and I have always been told that one if its advantages is the ability to reverse it.  I have an issue with one of my knee blocks on the Goddard tea table that might make me test this advantage.  The grain is not oriented correctly and I thought I might try and remove it and replace it but I have a couple of questions.  First, since the knee blocks on the table are relatively small and covered by a carving is it essential that the grain be oriented correctly (I think I know the answer to this one but I would like some more experienced opinions)?  Second, what is the best process for removing or releasing the joint?  Does the removal, because I assume you use water, damage/swell the surface of the leg where the new knee block would be attached?

Thanks,

Brian
 
There are several options.

If you did not clamp the joint, i.e just "rubbed on" the knee block, the glue joint will be weaker than the surrounding wood. You can usually tap it off with a hammer or lever it off with a clamp.

Apply heat with heat lamp or heat gun. This will often soften the glue enough to remove the knee block. Avoid getting nearby joints hot.

Steam the joint. This won't hurt the wood but if the steam gets to nearby joints on the leg they too may loosen

Drill a large hole through the knee block stopping just past the joint line. Fill the hole with alcohol/acetone or even water. This will usually loosen the joint.

Good luck.

Howard Steier
 
Since you don't want to re-use the knee block, saw or chisel most of it away, then heat gun it for a little while and the rest will peel off.
Mike
 
Regarding the question about the necessity of orienting the grain "correctly" - Note that whether you run the grain vertically (parallel with the grain on the leg) or horizontally (parallel with the grain in the apron), one of the two sides of the joint will be cross-grain.  While the usual situation on the antique originals have the grain runing parallel with the grain of the leg, there are exceptions, particularly on some carved Philadelphia tea tables that have a "swelled" apron whose ends serve as substitutes for the knee blocks.
 
If you heat up the joint just a bit you may use a syringe filled with alcohol and inject it into the joint. I have had good sucess with this process. In addition, you will not loosen other joints that are near by.

Mark Hickey
 
Don't mean to hijack this thread but have a question concerning the use of alcohol to loosen hide glue. What type of alcohol is used.  I saw this done by Bob Flexner on a video but the actual type of alcohol wasn't revealed in the video.

MIke
 
When I had to take apart a case I had made slightly oversized, Gene Landon showed me how he does it. He just took boiling water and a paint brush and liberally applied to the joints, waiting about 1 min and applying more. after about 5 min the dovetails slid right apart.

He said this works great for as he put it "new glue". With old glue he adds a heat gun.

I didn't notice the wood swelling, but it did raise the grain (a pass with a plane took care of that). I think by the time your done carving any rasied grain would be gone.

But this is the only time I've had experiance doing this, and I'm sure alot of the others have had a lot more.
 
Denatured alcohol would be my guess, unless you want to raid you brandy stash.
water and heat gun have done the trick for me quite a few times.

George Madok
 
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