Thread: Glue on top of glue

I dont know this for a fact, but I used to keep glue in a old sauce bottle with no lid over the tip, I used to get a small square of off-cut timber, squeeze glue onto it and leave it on top of the tip so the PVA sticks to the tip, over time the glue would build up into a thick layer of glue that seemed to be bonded to itself pretty good. However, the mechanical properties of said dried glue mess would be pretty weak I think.

edit: also, I seemed to remember people applying PVA or watered down PVA onto end grain, letting it dry, then adding another glue and joining as a way to increase end grain bond strength

It's all down to mechanical strength. Take two pieces of wood (preferably not soft-as-crap pine) and glue them to a piece of cutting board or something else that doesn't stick; use clamps as normal to ensure the bond with the wood half is as good as you can get. After 24rs break the joint; then glue the two pieces of wood together on those glue joints. Clamp as usual and then break the joint afterwards; it will break at the glue line as that is now the weakest part.

You get the same effect on joins where there is no close contact between the mating surfaces and the PVA ends up being used as a gap filler. Circular saw and jointer/thickness scallop marks reduce the contact area which is why cabinetmakers often use a handplane as the last step in edge preparation.