polyester and adhesion

I’ve been thinking for a while since I’m building my first board, and now I have a few questions waiting for an answer:

How good are the adhesion qualities of poly resin?

What kind of bond you get between foam and poly (chemical, mechanical, metaphysical) and how good is this bond?

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?

If the adhesion between foam and poly isn’t good, WHY (aside price) is used for board building?

Are the adhesion qualities of UV-cured polyester better than normal poly resin?

How good does poly bonds to epoxy? and epoxy to poly?

Any help is welcome, thanks to everyone in advance. Jack

for most stuff polyester resin is better thought of as a casting agent than a glue. It forms a casting mold on the surface of an object. There are few things with which it makes a true chemical bond.

So, the issue becomes surface preparation. Surface roughness helps a lot, and freedom from oils helps too. That is why you sand things rough before applying polyester resin (for ding repair).

Someone like Greg Loehr will probably chime in with answers to your other queries.

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

doc…

Bond to urethane foam is adaquate with polyester. Foams are all pretty easy to adher e to because of their cellular nature. Delamination in urethane surfboards is usually the foam coming apart from itself, not the resin /foam inteface breaking down. Now for adheision within the laminate itself, there are advantages to epoxies over polyester and certainly advantages in impact strength. The primary reason more epoxy isn’t used is we ahve an industry that doesn’t want change. Change will happen, whether it’s from consumer demandor from government mandate (1162 and MACT), but much of the industry will go kicking and screaming. Epoxies today however are ready for the change with systems that are very compatible with present production techniques and at similar costs. This change will also lead the way to different kinds of foam being used as well as high tech projects like Solomon’s S-Core.

J, The adhesion question has a simple answer: The bond is as strong as the weakest component, which is the foam.

No matter how strong the resin is after it’s bonded to the foam, it will pull away when the foam gives. I’ve stripped some boards to reshape them, and it’s not that hard to pull the cloth/resin off. I think the more important factor regarding strength is how strong is the “shell” around the foam. An example of a strong board is an epoxy/fabric shell around EPS foam: Weak foam + strong shell = strong board. Doug

The replies have been excellent. I have recently delaminated both PU/PE and

EPS/Epoxy boards for reshaping purposes. I had to pull really really hard to get the

Epoxy lam off, the PE lam pulled off soooooo easy, like buttah.

The diff was night and day. As GL has said in the past, epoxy has much

better adhering qualities and is more solid.