PE gelcoat-Epoxy resin in a laminate

General Composites Discussions Composites Talk
#1

Again to the debate of polyester gelcoat - epoxy resin in a laminate. I have read two very popular composites books and it seems that the authors have different opinions on this matter. More particularly:

Book #1:
“Epoxy gelcoats are available, but nobody seems to produce a clear epoxy gel. However, if you wish to make a clear matrix component there are a number of options open to you…
Or you could use a polyester gelcoat. Again, most people will tell you that this doesn’t work but providing you allow the polyester gel to cure well past the “still tacky” stage, epoxy resin will then adhere to it (extremely well) and cure properly.”

Book #2:
“The interaction between the epoxy used for laminating and the air-inhibited tacky surface of a polyester gelcoat is unpredictable-some formulations inhibit the cure of the epoxy, and manufacturers and formulators of both epoxy and polyester resins can generally offer no advice beyond “try it and see”. When i tried it, with a fairly common polyester gel coat and an even more common epoxy laminating resin, what i saw was not a happy sight. Despite leaving the gelcoat to cure for an extra long time and although both the gelcoat and the epoxy seemed fully cured, between them-right at the plane where the two met-was a thin, sticky layer of uncured something-or-other. With little effort, the gelcoat peeled off, like the shell off a boiled egg.”

So, what’s your own opinion on the compatibility between polyester gelcoat and epoxy resin?

#2

My experience was the same as the author of book two.
The only way to find out if your own materials are compatible is to try it.

#3

If you want to use epoxy with a PE or VE clear get Duratec they are compatable and make a PE and VE sprayable clear. There are clear epoxy gelcoats but you need to brush them on. spraying is much better, go with the duratec. just beware that the first two coats of Duratec you spray need to be lightly misted on because its very low viscousity, otherwise it will fish eye and run bad.

#4

I’ve experienced both. I will say that the clear per gel coat, and laminating epoxy resins from uscomposites were compatable. I ran into scenario two with the same per gelcoat and a higher spec resin from huntsman.

#5

Hey Hojo,

what epoxy coat is clear? and will it stay as a contiunous film on a semi perm treated surface? My experience is that a semiperm treated surface will not allow for a continous film/layer of anything, it will tend to break up and form droplets. (surface tension/repulsion…I don’t know)

#6

I am unsure the brand, contact composites ones, they told me about it as an option but I dont like brush on gelcoats.
as for the gelcoat fisheyeing/seperating it really depends on the viscousity. we spray gelcoat on semi-p molds with no problem, but we use a thicker viscosity gel coat then the duratec clears. Duratec clear is difficult to spray on to semi surfaces but can be done with a little practice. also most semi manufacturers have different line release agents, including one which are designed to spray gelcoat, they are not high slip but still offer a great release.