One question I am often asked by do-it-yourselfers who are faced with regluing a chair or reattaching some veneer is, “What glue should I use?” While the variety of glue is dizzying—Elmer’s® White Glue, Carpenter’s Glue, epoxy, cyanoacrylate (Crazy Glue®), contact cement, polyurethane glue (Gorilla®), hot melt glue, hide glue, urea formaldehyde glue, the list goes on—the choice for regluing original glue joins depends on many factors: What is the age of the object and what glue was originally used? Is there a possibility that the join will need to be reglued in the future? And what properties do we wish the adhesive to have? These are just a few questions to pose before deciding what adhesive is appropriate. However, in the restoration trade, a few adhesives come to the fore in making repairs to antiques and the list gets smaller for the do-it-yourselfer as we want first and foremost to be able to undo a poor first attempt, a common occurrence.
I've listed this glue first because this is the most commonly used wood glue. It is widely available in any hardware store under the names of Titebond Wood Glue or Elmer's Carpenter's Glue–and while the most popular, it maybe the most unsuitable for regluing loose joins on antiques. It is very useful in splicing in new wood to old, but in repairing old joins, future repairs are much more difficult to redo. Yellow glue (aliphatic resin) sets up very quickly, often too quickly in the case of chairs, before clamps can be put in position and tightened, making misaligned and out-of square glue-ups likely. For regluing, use liquid hide glue described below.
Most antiques (pre-1900) were glued together with hide glue, the glue we refer to when we suggest sending a horse to the glue factory. This is the gelatin part when you cook down bones and skin, pulling out the collagen to form a water-soluble adhesive. For restoration this is a blessing as old glue lines can be reactivated with hot water or thin hide glue to re-attach a failed glue joint. Even more helpful, it is relatively easy to remove during the repair process, yet doesn't need complete removal as new hide glue will stick just fine. Many veneered surfaces have cross-grain issues that will require periodic treatment of the glue line. Use of other adhesives will make this future treatment difficult if not impossible without serious damage to the surface. Yet hide glue will always be able to be made liquid again and, with adequate clamping, the veneer reattached to the substrate. So from a preservation standpoint, hide glue is perfect for regluing joins previously glued with hide glue. Even a bad attempt will still afford the future restorer or conservator the chance at making it right again.
Where do you get hide glue? First, you can buy cold, liquid hide glue (Titebond’s Liquid Hide Glue® or Old Brown Glue®) at some hardware stores, lumber yards and paint stores (it's used in creating crackle finishes) as well as online suppliers. For the occasional gluing, this is the easiest option. Put the glue on the pieces you plan on gluing and clamp for 24 to 48 hours depending on humidity. You can also make your own liquid hide glue or hot glue from scratch. It is no different than making gelatin (a more refined and higher strength hide glue). Go to "Making Hide Glue" for a more complete description on how to make hide glue. One warning: hide glue smells, not too bad to my nose but some are "riper" than others!
Another glue often used in the restoration trade is hot melt adhesive, the craft-person's go-to glue. Conservators appreciate this glue because it can also be reactivated, with heat alone, and it is soluble in mineral spirit, posing no danger to most original materials found on antique furniture. It comes as a solid cylinder that is fed into a hot-melt glue gun. Plug it in, pull the trigger and off you go. EVA is generally not used for gluing as much as for filling gaps. It will not expand or contract with the humidity and offers some flexibility. Squirted into a stripped screw hole, it will afford a good purchase. Heat the screw with a soldering iron, push it in, and the EVA will melt and solidify around it. Conservators will have no difficulty in removing or retreating this adhesive. It isn’t appropriate for regluing chairs or woodworking joins as it gels too fast.
Epoxies are very effective adhesives and are important tools in the restorer's arsenal. However, they require a fair amount of knowledge on how to use them and what to mix them with. They are also highly toxic before they are cured and require great care in keeping the material off of skin and of course all the tools we touch. Once cured, they are inert plastic.
There is a great assortment of fillers to change the properties of the epoxy to solve various problem repairs. However, the epoxy is not easily reversible or retreatable and must be used with great judgement. Epoxy is not for the do-it-yourselfer.
There are places for all the other adhesives on the market, but for the amateur reading this commentary, I suggest using those that will not make things difficult for the future repairman. I frequently get furniture poorly glued by the owner (or their handyman) that requires removing gobs of glue and sometimes original material just to make a sound repair. These adhesives have their place and I, myself, use a wide variety of adhesives appropriate for the task, but from a preservation standpoint, hide glue and EVA will rarely pose a problem should the repair need to be redone.