Here is the MAS FAQ:

http://www.masepoxies.com/Epoxy_School_/Tech_Support_FAQ.html

Note the chart, item #5, on curing. The cure time depends on the average temperature where your kayak is stored. Nick Schade has a photo in his book showing that he sometimes wraps his kayaks in black trash bags and lets them sit out in the sun. The curing time ranges from two and a half days to a few weeks.

That chart lists three times...pot life, the time it takes the resin to get hard (thumb nail time), and the cure time. I'm not in any way an expert, but I think you should wait until your resin has cured.

Cheers and good luck.

you should also protect the epoxy with a UV stabilizer or your nice clear epoxy will turn brown, cloudy and ugly.  you worked this long and hard so far.  Just throw at least three coats of varnish on her.  one more week of work.  You can always fine tune the finish later. 

Thanks for the info. I did read through cure schedule.  I know im pushing it but i really just want to take it out for a ride this weekend. My thought was make sure it floats this weekend... ha then next week put a few layers of varnish on.... I cant imagine the few hours of sun it will see will damage the epoxy before i can get some varnish on it? Which leads me to my next question. do i need to wait untill its fully cured to lay on the varnish? at my temp its calling out 7.5 days. 

I'm not sure about waiting for a full cure before varnishing. That's what I did on my Petrel, however, just to be safe. I was talking to my wife about this, and she pointed out that if I put my kayak in the water before the resin cures and/or the varnish was on and hard, I would be exposing the resin or varnish to not only salt water but any oil residue floating around the marina. And how, exactly, would I know that I got that off? I live in an area of Southern California where we have natural oil seeps floating in the ocean and washing up on the beach...

In my note, I neglected to see that you've got a SUP and not a kayak, and I didn't emphasize that if you get your SUP above 100F, the cure time drops dramatically. Why not stick it in some dark trash bags and let it bake in the sun? You could stick the working end of a thermometer in there and get a reading on the temp. Or, since it's a SUP, you could bring it into a small room and turn on a space heater... 

In finishing my Petrel, this stuff has really been frustrating. I didn't realize that after I finished the woodworking, the fiberglass, resin, sanding, recoating and finishing with varnish would take so long. But then, I realized that this is something I've been working on for six months and dreaming about for years, so an extra month is no big deal.

One thought. I used a smooth 6 inch foam rubber roller  to put on a few thin layers of varnish, and the finish has been mostly smooth, even and thin except for a few drips. The varnish dried in 18 hours, except for thicker drips. You could bag your SUP, speed up the cure and then put a thin coat or two on your board and then double back in a month or two and put a couple more coats on. I really don't think an outing without varnish will kill your board, however. 

I'm over budget. I bought a $50 quart of good marine varnish and it's covering my kayak with almost two and a half coats (I'll put the third coat on the deck.) That's going to be it for me now. I'm going paddling Sunday, I hope, and I'll double back in a few months and put on another layer or two when  my finances have recovered.

Cheers,

No problem (unless you live in the tropics) as long as you:

1.Wait at least until pushing the epoxy with your thumbnail doesn't leave a mark.

2.Are prepared to sand off and reapply the top layer of epoxy if it gets too grungy.

3.Keep the SUP out of sunlight except when you're actually on the water.

Have fun,

Laszlo

After thinking through it for a day, here's where I end up...and sorry I'm so long winded.

When you mix your resin, you start a chemical reaction that involves both chemical and physical changes. The reaction is affected by the temperature and which hardener you use.

If you look at that MAS chart, you'll see three columns, one each for slow, medium and fast hardeners, so one solution to this problem is to use a medium hardener if your curing temperature is fairly cool.

As the resin cures, several chemical and physical changes occur which result in the resin bonding with the wood and fiberglass in long chemical strings which result in thin, flexible and strong fiberglass. The changes happen rapidly at first, so the resin hardens in the pot after 20 minutes or so and then in an hour or so there's a point where the resin passes the thumbnail test. But the chemical and physical changes occur more gradually until they finally stabilize and the fiberglass will not react to varnish or the average contaminant.

If you put varnish on uncured fiberglass, you're introducing another set of chemicals on top of your still dynamic resin. That means another set of chemicals, which the fiberglass manufacturer did not intend to be a part of the process, is now bonding with your resin. That will permanently (I think) affect your fiberglass in unpredictable ways...not necessarily bad but not necessarily good, either. Likewise, if you put your uncured resin in the water before it's cured, unpredictable things can happen, and if your board or kayak should be paddled past an idle outboard that's leaking oil, or past some other polution, that stuff might bond with your resin.

I think the longer you wait for your glass to cure, the better. In my original note, I was kind of assuming that you would be curing your board somewhere between 100F and 70F, but in fact you can speed up curing by heating the board.

Surfboard manufacturers use fast hardener, by the way. One interesting thing with MAS resins is you can mix different speed hardeners. If you're making a kayak or SUP board in winter climate, you can use medium hardener to achieve more reasonable cure times.

Cheers