as long as your shop is dry and warm, its ok if it's raining outside.

that said, you definitely do not want a sauna-kind of condition (misting, sticky, etc.) but if its just a cold rainy day and  you are working inside in a heated shop....you are fine.

the only other comment i would make, since you mentioned the cold,  is do keep your expoxy at room temperature or above at all times.  if you are building in the winter and heating up your shop for an epoxy session, you do not want to leave epoxy stored in the garage when it gets super cold.  bring it inside.

Thanks very much for your quick reply! I thougth that it would be okay but it's always good to have validation from others. I should  have been more clear in my information. My version of "cold" is really far from true cold - I live in Northern California and, well, cold is a relative term! :)  I'll be sure to heat up he epoxy before use - I usually put a 40 watt light bulb behind/ under it for a while before the session to make sure it's nice and "loose". 

It's a small job that I'm undertaking, and as such I'm not going to worry too much about the shop being as warm as I would when glassing the entire hull or deck. The thin strips i'm applying won't really show in this case so it's not too much of an issue. 

Thanks again!

Rob

 I looked up the FAQs on the MAS website and found the following:

12. Temperature requirements?

For clear coating, we like to see the resin remain over 55 to 60 F. For bonding, anything over 45 F is adequate.

I too live in NorCal and am ready to fiberglass the hull of my Chesapeake. I am in no rush for cure time but would like to at least get it applied. The weather will be this way for a while but it is within MAS temp range. I too was wondering about CLC idea of "cold" on the East Coast vs West Coast.  

Hey Rob,

I'm not a fiberglassing expert, but I'd definitely hold off on tackling that coaming riser if the rain's coming down outside! While you might be dry in your shop, even with the door closed, humidity can definitely play a role in how well the epoxy cures.

Maybe check the forecast on [isitgoingtoraintoday.com] to see if there's any chance of a break in the rain soon. If it seems like it might clear up later today or tomorrow, it might be worth waiting for better conditions.

In the meantime, you could always tackle some other project prep work that doesn't involve the epoxy.

Good luck with your build!

I'm going to respectfully disagree with TrailBlazer89. Epoxy cure problems in high humidity depend on the type of epoxy. Older formulations that had blushing problems would blush worse in high humidity conditions, but modern no-blush formulations don't care.

Scouring the internet I came across many versions of the same article (each with a different set of typos) warning against humid conditions. Apparently a lot of people find a version with google and then just incorporate it into their website without chasing the facts down. Pretty much every version that I found was referring to casting, tabletop and art epoxies. I say pretty much because some did not reference a specific epoxy.

But when I filtered the search for marine, no-blush, low viscosity laminating epoxies, like MAS, System Three Silvertip, etc., none of them warned about the humidity. In fact, System Three specifically says "Use at temperatures as low as 35°F with no limitations on humidity. Even at lower temperatures and higher humidity this resin will not blush on curing."

So my take-away is that epoxy products based on older blushing formulations can be affected by excessive humidity, but that the modern no-blush formulations (like the MAS epoxies sold by CLC) don't care about the humidity, just the temperature.

Laszlo