I have always used epoxy so polyester is new to me, for clear boards I usually apply a filler coat of 200mls of epoxy but it doesn’t buff up as well as polyester. I recently tried using polyester(the filler one) over the epoxy laminated glass as my supplier told me that the poly would bond to his epoxy. O.k. so I mixed up 200mls polyester with 3% hardner on a 24 degree day and rolled it on the bottom (of 8’6" board) as I would the epoxy. The next day I went to do the other side and the resin was like hardish sticky toffee, Heaps of acetone and a rag got it off. what did I do wrong??
maybe your catalyst is bad. get some fresh & try again, 3% should have kicked it easily; I never use that much…
Hmmm… are you using sanding resin? It almost sounds to me that you are using laminating resin. Poly needs a sanding agent added to it so it is not tacky, and ready to be sanded. You can also buy to kinds, laminating and sanding. Thats my best guess. -Carl
yep was sanding resin the stuff with the wax in. I’m wondering was the layer to thin and it didn’t generate enough heat to help it go of.
You can actually overcatalyse resin, causing the chemical reaction of hardening to go the other way.
General recommendations from polyester resin suppliers are 1-2% from memory.
Old resin and/or catalyst or impurities in the mix can also behave this way in my experience.
Sounds like to me thay you over catalyzed.Old catalyst can give you problems as well. Remember, it’s much better to measure twice. Catalyst doesn’t necessarily fit into the category of “more is better”. McDing
Sand the resin abit it’l get rid of the stickyness(i think) this has happened to me before when i was doing a ding repair with epoxy i used an eletric sander and then it was fine.
josh.
Sounds like old catalyst. Catalyst goes bad, and doesn’t work at all. If you think there’s a chance that you have some old catalyst, it’s best to do a gel test.
Your poly more than likely did’nt go off because you put it onto a epoxy laminate. Poly will not adhere to epoxy. Sometimes it will not even gell. I’m speaking from a boatbuilders point of view, with over 20 years experience in the composite boatbuilding industry. I’ve said this before you don’t get a mechanical or physical bond, when poly is applied to epoxy. If it goes off, you get an initial bond,but it will eventually fall off. Better off sticking to epoxy, or spraying a auto clear coat over the epoxy and buffing that. Bert Burger uses some sort of clear coat over his boards, can’t remember what it is called. It’s much harder than auto acrylic. Hope this helps.platty.
Thanks for your info platty I had heard that poly won’t stick to epoxy, but my epoxy supplier told me it would so I thought I would give it a go. I guess I learn’t the hard way.
I did see one of Bert’s posts ages ago and I think he called the stuff Upol I’ve never heard of it before.
platty’s right on this one. There are epoxies that won’t even let poly’s start to gel. I bought some really cheap epoxy for stubborn stringer glue-ups in polyurethane blanks. When I glassed the boards they had a ribbon of completely wet resin over the glueline next to the stick. I was baffled, I called GL (Mr.Tech) and ran it by him, he had the answer, cheap epoxies have a thinning agent in them that makes them completely in compatible to polyester
OK there goes that idea I had! I’ll keep fill coating with epoxy it takes longer to go off, is more expensive and I am concerned with the hazards of sanding not fully cured epoxy. I believe it takes a few weeks to fully cure and is quite tough to sand if I could wait that long.
I bailed on the 2 method way of doing epoxies. I tried poly over epoxy and had the same disasterous result, no go off. I reverted to a COMPLETE epoxy board and got a much better product by doing so. Save yourself money by spending more on Greg’s really good resin. It sands like poly with his sanding additive, I haven’t had anyhthing I could remotely call a reaction to the dust or resin. I do try to act in a sensible manner and keep my exposure to any chemicals to a minimum
At least one company (System 3) advertises that they have a formulation that works with a poly overcoat… there are so many proprietary formulations among different companies, it’s hard to generalize.