How good are the adhesion qualities of poly resin?
Well, compared to what? And on what… not to be a wiseacre, but it varies a lot.
What kind of bond you get between foam and poly (chemical, mechanical, metaphysical) and how good is this bond?
Metaphysical, definitely… nah, it’s a mechanical bond, the resin gets into the pores of the foam, the open cells, and kinda locks it in. How good is this bond? Well, usually when the bond fails ( the fiberglass/resin breaks away from the blank) it’s 'cos the foam itself failed and some foam still adheres to the glass/resin laminate.
If the adhesion between foam and poly is good, why it doesn’t bonds well to wood? I’ve read that the oil in some woods is the problem, but what goes on with wood with no oil?
Complex question, partial answer; the poly resin doesn’t necessarily penetrate especially well into the wood and so the surface layer of wood peels away. Other contributing factors include but are not limited to moisture in the wood, resin too thick to penetrate at all, chenmical reactions wood-resin, greater absorption of resin by the foam ‘drying the glue joint’ as you can get in end-grain gluing of wood-wood. Complex situation, can be one and can be several.
If the adhesion between foam and poly isn’t good, WHY (aside price) is used for board building?
Another partial answer to a complex question:
Surfboards are a low-profit industry. Developing new construction systems and methods is done mostly outside the ‘industry’, by smaller entities than the major companies building boards. It’s kinda tough for somebody building a few boards a year to go to a large company that makes resins or foams and get them to make up something specialised when there’s such a small demand. Most major materials/methods changes or advances are guys adapting stuff made for other purposes to surfboard use which then gets more fine-tuned with time and increased demand.
While polyester resin/polyurethane foam might not be the best available technology at any price, it’s an adequate technology that can be used in a very low-tech way on the cheap. A guy with a bucket, a squeegee, a stirring stick and a brush can glass a board pretty well in a relatively wide range of ambient conditions. It can be tweaked to work in less than ideal conditions pretty easy, it’s a relatively mature technology. We’re not talking ( as in some carbon fiber/epoxy laminates ) about the need for a pressurised autoclave here or complex heating elements.
Then you have market resistance. The surfboard buyer is kinda conservative that way, he wants a board he’s relatively familiar with, especially after ( historically) so many new board building technologies have turned out to be such resounding flops.
And that’s a partial answer…
Are the adhesion qualities of UV-cured polyester better than normal poly resin?
Haven’t used it, though I am given to understand that it’s equivalent.
How good does poly bonds to epoxy? and epoxy to poly?
I’ve done very little of this, and it varies a lot with which epoxy and polyester resins you use, surface prep techniques used and such. But bear in mind that it’s a mechanical bond.
Generally, the epoxy has a higher tensile strength than polyester. That is, under a given tension, it stretches less than polyester. So, in use an epoxy stuck to a polyester laminate is gonna break loose as the polyester stretches while a polyester stuck to an epoxy laminate is going to stay put.
Hope that’s of some use