The Best Way to Reglue Furniture

Disassembling and Applying Glue
A better practice is to disassemble the joints before applying the new glue ? usually white, yellow, epoxy or polyurethane glue. This method exposes more surface area to these glues, so there’s a better chance that the joints will remain tight for at least a few years.

But the wood is still sealed with the old glue, so just as with the previous method, whatever bond is achieved is made to the old glue, not to the wood. The bond achieved is thus no stronger than that of the remaining old glue to the wood, and that glue has already given way once. Moreover, when the joints break down again, as they surely will, proper regluing will be much more difficult because all the newly applied glue will have to be removed in addition to the original glue.

Using Hide Glue
All furniture made or repaired before the 1950s was glued with animal hide glue. This glue is made from the broth of animal skins, usually cattle, and has to be heated to about 140 degrees to be made liquid. Animal hide glue has the unique characteristic of dissolving quickly in hot water.

Because hot hide glue is both hot and wet, it dissolves old hide glue when applied over it, and a strong bond to the wood is usually achieved without the old glue having to be removed first.

The great advantage of continuing to use hide glue in joints glued originally with hide glue is that regluing is fast and very effective. When hide glue was the only glue available, everyone used it, and this is surely a primary reason that so much very old furniture has survived so long. Most of the old-furniture joint problems you see today are the result of one of the three lesser-quality regluing methods (discussed above) having been used.

The product called Liquid Hide Glue is the same as hot hide glue, except for added preservatives (to keep the glue from rotting for about a year) and gel depressants (to keep the glue liquid at room temperature). It can be used fairly effectively in place of hot hide glue as long as it is first heated to about 140 degrees.

Cleaning Joints
An even better practice than using hot hide glue over old hide glue is to clean all the old glue out of the joints before applying new glue. The strongest bonds are achieved when the wood is totally clean. This was the condition that existed when the joints were first glued.

Once the wood is clean, any glue can be applied, and the result will be strong, long-lasting bonds. The only rationale for using hide glue at this point rather than another glue is that the joints will be easier to reglue next time.

There are two ways to clean old glue off of wood: dissolve it off, or scrape or sand it off. Dissolving is the better method by far, because it’s totally effective and doesn’t change the dimensions of the parts. Because the old glue has penetrated somewhat into the wood, it?s not possible to scrape or sand off all the glue without also removing some of the wood, and this creates air spaces in the joints. Tight wood-to-wood contact, which is necessary for a strong bond, is lost.

Hide glue is the easiest glue to dissolve and wash off. White and yellow glues are next. Each of these glues dissolve or break down in hot water or vinegar. Epoxy, urea-formaldehyde (plastic-resin), cyanoacrylate and polyurethane glues have to be scraped or sanded off because they can’t be dissolved.

Not all furniture is deserving of the time it takes to reglue with one of the better methods, but all better quality furniture is. PW

Bob Flexner is a contributing editor for Popular Woodworking.