Overnight epoxy application

[HarryinSC]

Okay, here’s my scenario:

I am planning to fiberglass the outside of the canoe this weekend.

Daytime temperatures are around 72, overnight temperatures down to 55. I have an unheated but partially insulated garage that seems to stay above 63-ish.

This epoxy has a set time of 3-4 hours, and a dry time of 8-10 hours. This is at ideal temps of 80.

I can’t imagine getting all 3-4 coats of this thinner epoxy done in a single day, since set time might be extended to something like 5 hours?

I am considering getting a jumpstart by applying the wet out coat late in the evening, and then starting on coat 2 the next morning. This would mean about 10 hours between coats, but it will be cool-ish the whole time - probably around 65. Do you think the epoxy will still be tacky in the a.m.? Any downsides of the cooler temperature in the quality of the finish?

Thanks!

Harry

[Cruiser]

Since you don't actually share the epoxy brand etc. any response is just guessing on my part ... but that won't stop me making suggestions.

I routinely use East epoxy which has a similar setup time as whatever you are using (3-4 hours). I wouldn't do a "night before" coat .... and I don't use a pre coat, IMO it is a waste of time .... having said there are others who feel it has some value, so your choice.

My routine is to get the glass on the boat and covered with a clean plastic sheet, the day before glassing.

I then setup a work area exclusively for the epoxy prep, I get the mix area all setup with mixing cups, stirring sticks, rollers, brushes ... you get the idea. If you want to keep the canoe a bit warmer, maybe put a small ceramic heater on the floor under the canoe, that will keep the hull warmer for application.

Fiberglass day starts around 9:00 ... pull the plastic sheet and start mixing ... the first application should done around 10:30

Second coat (fill) ready to go on some where around 14:30, this one is faster .... as all you do is a coat and wait for to kick and then squeegee, maybe an hour, so done some where around 15:30

Third coat, heavier with no squeegee, so it is fast as well .... should take less than an hour to apply and it is going on somewhere around 19:30

So last coat is going on after supper, say around 7:30 ... makes for a long day, but it is quite doable. I would consider leaving that little heater under the canoe for the whole time, doesn't need to be on full, just enough to keep it a bit warmer.

I have never needed to go further than 3 coats to bury the weave, so hopefully you wouldn't either. If more coats are required, I would contact the manufacturer and get some advice on how long between coats is allowed for full chemical bond, they are the ones who should really know that sort of stuff.

Brian

[Cruiser]

This is a link to my last build, where I do the fiberglassing, you may find something of use there

https://www.canoetripping.net/threads/l ... ost-107377


Brian

[HarryinSC]

Brian,

Thanks for the information and link. I’ll read through your experiences thoroughly.

I’m using fiberglass and epoxy from US Composites. It’s their 635 thin epoxy system with medium hardener. I asked how it compares to West Systems, and they said it’s thinner. I assume wet out won’t be any trouble, but it may require an extra coat or two to fully bury the weave… we’ll see.

After pondering the timing more, you’re absolutely right. I’ll heat the space a little and get started early, and I think I’ll be able squeeze it all in without any trouble. I guess it partly depends on how tacky it should feel before starting a new coat. I did a test application last night on a scrap piece, and it was still tacky/soft enough 8 hours later that it was easy to dent with a fingernail and some picked up on my fingers when I touched it.

I really appreciate the guidance.

Harry

[Cruiser]

IMO (no experience with US Comp product). tacky is fine for subsequent coats, as long as it is mostly setup.

One other point, don't just glass and walk away, babysit, checking at regular intervals for bubbles, bugs and runs, those can all be largely corrected by catching them before the set is locked in. Have a heat gun handy to help pop bubbles that may form in the first bit, tweezers for strays bugs and a clean foam brush for runs.

The caveat to chasing small issues, is to know when to stop .... once the epoxy gets past the honey stage, leave everything alone ... unless there is a bubble you think you can still get, epoxy flows (albeit slowly) for a couple of hours after application.

Brian

[Jim Dodd]

Temperature definitely effects cure time !
I think you have a good plan, to glass towards evening, but as Brian states, don't walk away from it !
I have a few memories of doing just that, with regrets.

A thin epoxy will require more fill coats. the System Three, Clear Coat, I used required two extra coats. That made it more expensive to use. It was however a good epoxy !

Back to your plan. Applying fill coats goes faster than the wet out coat.

After a fill coat is applied ? You need only wait an hour, or two, and you can apply the next coat. I prefer foam ( Cigar type foam rollers) The good ones, made for varnish. I get an even coat, without epoxy running down the side

You always want to apply a fill coat, while the previous coat is still tacky ! This prevents the majority of the runs, that are common with epoxy.

Have everything ready before mixing that first cup ( I mix 9 oz batches ) !!! Keep moving, and get the mixed epoxy on the hull.

Good luck !

Jim