IS YOUR FURNITURE VENEER OR SOLID?
Solid wood will have “end grain”. Veneered furniture has an edging applied, either a solid wood boarder, or an edge “tape” of solid wood. Veneer on commercial items is typically very thin, up to 1/64″, and while this does maximize the quantity of items a tree’s beauty can be transposed upon, it can also greatly reduce the refinishing options available. An inattentive hand can quickly cut through this thin veneer when removing the old finish, which (if power sanding) can quickly expose a large blotch of MDF or plywood. If you’re planning to refinish your own veneered furniture, try and practice removing the old finish and stain in an inconspicuous place
WHAT GLUE SHOULD BE USED?
Yellow wood glue is the preferred glue. It is a PVA (poly-vinyl-acetate) glue with Aliphatic Resin added to increase its water resistance. Basically it’s the same white glue you used in Elementary school, with a yellow add-in to make it stronger. This glue works extremely well when it is bare wood to bare wood, on well mating surfaces. If either of those conditions are not met it won’t work for long, because it has a high adhesive strength (it’s ability to bond to wood) but a low cohesive strength (it’s ability to stick to itself) and is also mostly water. This means if you try to reglue a dowel connection two parts of a wobbly chair, you had better remove the glue from the dowel and the hole it goes into, and that there should not be any play, or movement, when the two pieces are dry fit (without glue) together. They should go together with firm hand pressure, not loosely, because as the water evaporates and the glue cures, it shrinks considerably, leaving very weak hollow areas where there is no wood-to-wood contact. After gluing two pieces together, you can use clamps, tape, or even bungee cords, to hold the pieces in position as the glue dries. Make sure not to put so much glue that you can no longer fully seat your pieces together. Squeeze-out should be wiped off immediately, and thoroughly, with a clean, damp rag.
Polyurethane glue on the other hand, has some “gap filling” properties, as it will expand like foam insulation anywhere it can as it cures. This glue is a good fit if you have removed the old glue from both mating pieces and there is a little play. It is activated by moisture, and very messy if you get it where you don’t want it, so be sure to put masking tape around the joints you are gluing to avoid a headache. Cleans with Acetone.
Epoxy Resins are an expensive option, but probably the best for ease of use and speed of operation. Epoxy will not increase or decrease in volume as it cures, so it will fill any gaps in joints*, it has much higher cohesive strength than Yellow Glue or Polyurethane, and it will stick to most clean surfaces that are “scuffed up”. scratch a piece of steel with a hacksaw blade until it is uniformly scuffed, clean it with a grease remover like acetone, and pour epoxy on it. The other glues will pop off, the epoxy won’t. This means you don’t need to worry about removing the old glue before joining pieces, you need only scuff/rough the surfaces up to give the epoxy something to bite into. Cleans with Acetone.
Protein Glues have been used by every culture since time immemorial. The most ubiquitous are made from animal collogen, hide glues, fish glue, rabbit glue, they all have their own specific properties. The benefit of these glues is that they are edible (food safe) and reversable. Stradivarius’s fiddles have survived to this day not simply for the fact they were a prolific builder, nor that they have been carefully handled through many hands, but due to the fact that fastidious Luthiers through the centuries have been able to disassemble and reassemble these working art pieces with ease.
Many other protein glues exist. You are probably familiar with Paper Maché, which gets it’s sticky characteristics from the protein gluten, but did you know that glue is also made from milk? The casein protein in milk has been found in glue and paint going back centuries. It sticks so well, in fact, that “milk paint” is a real thing you can apply to your furniture today! There are rice glues and glues derived from tree pitch. All of these ancient glues has its own benefits and techniques.
*as long as it doesn’t leak out of the joint! it is often thick when applied but becomes quite thin and fluid at the start of it’s curing process. Make sure the piece is positioned in a way that it will not leak out of the joint