I sometimes have problems when gluing up 24/4 or thicker stock for turning squares. While all the joints may appear to be tight when the work is clamped, some of the glue lines open up later. It appears that the moisture from the glue is expanding the glue side of the outer layers, creating stress in the form of cupping that opens the joints. I learned the hard way that Titebond II is not structurally rated when I had problems with square turned porch posts and staved porch columns with glue lines opening up days or even months after turning and installation.
I've used structural epoxy to get around this problem but this is rather expensive. I have heard for years that you can starve a glue joint by using an insufficient amount of glue but I wonder if putting too much glue on would cause the theoretical wetting/tension problem. I am looking for advice on a cost effective adhesive for gluing up thick turning stock. I have also noticed that the harder woods prove more challenging to glue up into stable stock.
From contributor A:
I have noticed over the years that fat solid turnings do not age well in interior environments, and ditto/double for exterior work. The unavoidable humidity cycling will eventually cause cracks to open up in the wood, if not glue lines. The mechanism is shrinkage, similar to the way a whole log cracks as it dries. A 24/4 chunk works out to about 6", and I would question the MC starting out. If it is high for your area, then no glue will hold it. I try to hold solid exterior to 4" or less and hollow above that. Interior can be up to 6" solid, and hollow over 6". I use epoxy or resorcinol glue for exterior. I'd rather stay on the safe side.