…putting polyester gelcoat directly over their epoxy is a BAD idea, even if you do the scrubby scrub wash off the blush thing.
Bad.
very bad
sooooo bad!
So what is it about Resin Research and System Three SB112 that lets polyster work over them, the cycloaliphatic chemistry?
goes back to scrubbing with Scotchbrite and acetone…
…putting polyester gelcoat directly over their epoxy is a BAD idea, even if you do the scrubby scrub wash off the blush thing.
Bad.
very bad
sooooo bad!
So what is it about Resin Research and System Three SB112 that lets polyster work over them, the cycloaliphatic chemistry?
goes back to scrubbing with Scotchbrite and acetone…
Why would you want to put polyester over epoxy? Personally, I don’t think you can put even west system on top of west system and get a good bond if not sanded very well. Secondly, DON’T USE ACETONE WITH EPOXY. NOT EVEN FOR SCRUBBING. It leaves the epoxy in a gooey state which screws up any bond to anything. (Let alone if you use it with uncured epoxy, which is a toxic mess). Use rubbing alcohol or denatured alcohol instead, whatever it’s called where your are. For the blush, soap and water is better. For finnish, use a laquer or polish the final epoxy layer.
Good luck.
regards,
Håvard
Hi Patrick,
It’s been my experience that WEST system claims are rarely borne out in use. Especially ‘claims by users’ that somehow find their way into the company literature.
I still have a bunch of that RAKA left, if you need any
Best regards
doc…
I was trying to finish off that Pang with a nice hard, durable coating, without using a 2 part LPU paint, which scares me and my wallet. I dropped Tiger Canoe a line to ask how they finished their boards, and all of them use a gel coat. I know, I know, using gel coat in a mold then putting epoxy on top of it is whole a different story than putting gel coat on top of epoxy. But West System said it would work, so I believed them and went by their numbers.
I tried little test patches of five different one part paints for finishes, and none really seemed up to the task. They were all either too dark (it’s surprisingly difficult to find a very very light grey, really just an off-white), or too soft. So finally I just ordered a quart of waxed gel coat, and added a little grey pigment until I had a nice match. As you might suspect, it worked fine over the old gel coat, which I’d sanded and wiped down with styrene just before application. But over the epoxy, not so much. It just never cured. It probably would have worked if I’d primed the epoxy with something, but… I’d read that I could get away without doing that, so I tried it. Bah. I know System Three SB112 would have allowed it, because Doc gave me some to try last summer while I was repairing a Force Field lifeguard comp board, and I put a polyester gloss coat over the epoxy repair. Worked great.
Anyway, I had to get the uncured gel coat off, so I used a putty knife to scrape most of it away. Then I tried working my way up the line of nastiness. Soap, no. Mineral spirits, no. sigh Acetone, yup. So armed with my organic vapors mask and nitrile gloves, I went over the remaining residue with a Scotchbrite pad and some acetone, quickly wiping up the loosened mess with paper towels. It was not my preferred method, but it’s what I had, and worked. I sanded the cured gel coat fair, and I’m going to have to go back and do this again another way.
As a point of note, Duplicolor Engine Enamel spray paint works very well when painting over epoxy. It dried hard, sticks well, and it’s very resistant to chemicals. And it’s very economical, especially in comparison to marine paint systems. I used Daytona Yellow when repairing Force Field rescue boards, and it’s a great match. Unfortunately, they don’t offer one in the color I need for this project. I checked out some epoxy spray paints for painting appliances, but nothing’s close on color.
I think I’m going to give Rustoleum Marine paint a try. It’s available locally, and it’s reasonably priced. I believe it’s a modified alkyd enamel. I’ll also see if the store offers a nice durable 2 part industrial paint.
I really prefer to finish the board well. I did a nice job on the repairs. It’d be a shame to have a paint that scrapes off when it gets dragged across the beach. I’ve read on a kayak building forum and a couple of boat sites that using porch and floor exterior enamel works nicely… shrug
hi patrick,
although i agree in principle, i’m a little confused.
the epoxy should cure to a hard compound regardless of what comes next.
if its something like West that has lots of blush residue you need to wash that off, as stated.
however, once done, anything gooey is probably uncured which brings the quality of the entire laminate into question.
it may not be cured yet.
it may not be completely mixed.
it may not have the correct ratio of resin/hardener.
the fact that the epoxy is supposed to cure to something relatively inert is sort of a double edged sword.
i believe that is why you will not get a good bond with subsequent layers of PE or even epoxy.
on the other hand, inert also means it shouldn’t interfer with the cure of other layers.
good luck,
-bill
I use a three beam balance to measure out resin and hardener, I mix and mix and scrape sides and mix and mix (and mix and mix) before applying. It set up in the time I suspect it would, it sanded nicely with no soft spots, and I let it sit for a week before applying the gel coat. It cured in a nice dry room heated to 70 degrees.
I scrubbed the cured epoxy down with water and a Scotchbrite pad as West System said to, then rinsed while still wet, and dried by hand with paper towels so no residue would dry on the board. I did not use ammonia or soap, as they specifically say not to.
I really don’t know how much more careful I could be than that. I suspect epoxy is not quite as inert as some like to believe, and that the styrene in polyester resin leeches some of the amines out of the epoxy.
Of course, I could be wrong. What I do know is I was very careful, followed the bouncing ball, and it didn’t work. Time for plan W, or something. 
Ah, Patrick, I still have enough of that SB-112 left to do it , if you want to put an intermediary coat on there, and you’re welcome to the stuff. Also, I have some white pigment, just put that in a clear (as opposed to the s#hit-brickle-brown WEST cr@p ) epoxy and add a touch of cabosil for thickener ( for non-sag ) and there ya go, instant epoxy gel coat.
Works for me
doc…
so sorry.
…and lastly
i may just be the crappy epoxy you believe it to be.
-bill
Eh, it’s not that the epoxy is bad, it’s just that the two materials don’t seem to work well together.
I think I’ve got this one solved though. 
Here it is, two coats of this done, and wetsanded. Third coat on now.
