TOPIC: Gel Coat sticks to Epoxy !?

This test kinda changes the age old rule, don't you think???

excellent tutorial mark...

I'd be interested in seeing a gelcoat/epoxy sample put thru a 1-2yr duty cycle to see how it holds up over time thru multiple temp cycles.

Don't epoxy and gelcoat breakdown differently over time? How would that effect the bond?

I like his series of BoatWorks videos, he does nice work on both the boats and the videos. An excellent resource for sure.

Very good point / question John, this test does not cover the longevity aspect of the equation, guess we'll have to wait until someone is brave enough to try it in a "real life" situation.

I agree, they do an excellent job on the videos IMHO. Novice friendly and unpretentious.

Having never done any fiberglass repair, Ive found his videos informative and have given me some confidence, for when I get to that point in my project. I bookmarked his home page sometime ago.

boatworkstoday.com/

The other thing to note is not ALL epoxies are the same. West Systems actually make their own special blends and they ARE formulated to be better suited to work with Gelcoat. But even they will tell you if you speak to their techs that when doing major gelcoating projects for below the waterline Polyester resin is still the better choice. If you purchase an OFF BRAND of epoxy you may get total failure when attempting to get Gelcoat to adhere to it or at best it may work for a short while.

I found this info on the internet a number of years ago.

www.westsystem.com/ss/polyester-over-epoxy/

Even though this research had been done in 2004 by West Systems, I have to assume it's still current as it's still on their website.
Obviously West has a lot to gain by putting a positive spin on it, but the science seems to be valid. It's been over 10 years since this test was done. It would seem that West has had enough practical experience from the field to support it or they would have modified it by now, but
it sounds like the West service techs may have a better idea of what actually goes on in the trenches than management, and are are taking a little more conservative view on repairs to boats left in the water continually.
I think the most important part of the gelcoat over epoxy discussion is to understand that it's a mechanical bond, not a chemical bond and that a chemical bond is easier to get right than a mechanical bond.
As My Flamingo says, not all epoxies are the same and using a good one is important along with correct surface prep to get a reliable bond when using gelcoat over epoxy.

Don

Also good points gentlemen, thanks for the input. Not sure I'm brave enough to even try the gel coat application, but I do appreciate the civil conversation of the subject!