fiberglass resin cure time

HI. Quick question for those of you who have done a lot of glasswork. I’m using fiberglass resin for the first time, patching a crack in a surfski. Bought a “kit” from Oak Orchards, so I don’t really know which resin it is, or what the cure time is supposed to be. Followed the directions, 5 drops of catalyst. It’s been about 24 hours now, and it is still fairly tacky. Seems to have set up, in the sense that it is no longer running, but it is definitely still soft. I’m doing this in my basement (decent ventilation) which is probably at about 70F, very humid right now with all the rain we are getting.

Is this normal? I’m not in a rush, but I just want some reassurance that this stuff will eventually harden up so that I can sand it, etc. Do resins take this long to cure?


I am guessing that…
…the humidity is slowing the process down.

When I have used it, it would be rock solid overnight.

However, last year down in Florida in the humidity I used some two part Epoxy to repair a k large crack and two days later it was still tacky



Yup. Humidity.
The bane of polyester resin. I am no expert, but in the days of my glass boat repairing I suffered the same problems. You might try warming the repaired area with a flood lamp (don’t overheat - if it is too hot for the back of your hand it is too close) and DONT use a “heat” lamp. I have also swabbed the sticky area with catylist, but that was in desperation.


A bit more catylist
when it is humid help a litte. They also make resin for humid environments, it is supposed to cure faster in high humidity.

good luck,


If it’s “epoxy” resin…

– Last Updated: Jul-11-05 9:09 AM EST –

It should go off in 12 hours. Heat might help.
West Systems makes an epoxy repair kit in little foil packs that works well for small repairs.

also if it is not mixed really, really well you may have problems. Mix for one full minute.

Read closely, everyone!
Afolope said “5 drops of catalyst” so we must assume that the resin is POLYESTER rather than epoxy.

Most polyester resin used for repairs is “pre-promoted” meaning that given enough time it will harden (you already experienced that with the old resin!). If you have the time, let it sit. Sun is good if you can leave the hull outside while you are away.


glad that I don’t fiddle with resin anymore

It will take time
The catalyst does have a ‘shelf life’, so really you should have used new catalyst. As long as you mixed it thoroughly, though, it’ll (probably) eventually cure. 5 drops should have been used with about 1/2 oz of resin. How much resin was used? If you had more resin, and old catalyst, then that probably is why it’s taking so long.

It should take no more than 2 hours to cure with a 10-12 drops per oz resin, at around 80 deg. (there are a few other factors, but that’s close enough for a fairly solid cure where it’s sandable).

Yes, and the other awful thing about
promoted polyester or vinylester resin is the way they will turn to useless gel in the storage container with time. West epoxy does not do this, though with age, it will thicken slightly and come out a dark red color. Great for mahogany repairs. no longer offers polyester resin because it isn’t that good. Vinylester is a great material for making an entire boat, but not for sitting around in storage until you need to make a small repair. West epoxy and the pumps… worth every penny.

As are Raka epoxy and pumops.

What type of resin?
The common “laminating” resins will not get hard on the surface if they’re exposed to the air. The underlying resin WILL cure and the patch will be hard, except on the surface. That’s why the instructions that come with laminating resins tell you to cover the patch with Mylar, to isolate the repair from the air. An alternative is to spray the area with PVA mold release.

If you use a “finish” resin, it will have a wax additive that seals the surface automatically. You may also be able to find the additive separately.

not sure
it’s a pain for me to get to west marine, so i (in retrospect somewhat foolishly) ordered a “kit” from oak orchard. i have no idea what brand of resin it is, and at this point it is a bit late to worry about it.

the resin continues to slowly but surely set up- it is basically dry to the touch now, and the smaller patch is getting hard. the larger one is still a bit soft. i’ve moved it into the sun now, as the deluge seems to have ended, and i’m hoping a bit of time in 90F weather will do it wonders. i may throw some wax paper over the areas if it seems like the surface isn’t setting up right.

progress, progress, progress…


ditto on the humidity

Bnystrom, I have not had that experience
because the West epoxy patches I have done WILL get hard and non-tack on the surface without use of a film covering. Oh, there may be a slight gummy feeling from the amine blush, but the surface of the patch is hard.

s/p 12 hours in the heat and sun- rock hard all over. i’ll give it another day, but that definitely did the trick. thanks to everyone for your help.



With epoxy, sure.
Epoxy cures fine in the presence of air. Polyester resin, which is what Afolpe is using, is another matter entirely.

Have used very little polyester, but the
vinylester and glass patches I did all over a friend’s Noah Atlantis all hardened properly in the open air. Am I missing out on a frustration I deserve?