Short answer: yes for PVA, mostly no for epoxy, and the reason comes down to how each glue actually cures.
PVA (Titebond, etc.)
PVA glue is a water-based emulsion. It doesn’t cure through a chemical reaction between two parts; it sets as water leaves the glue line, either evaporating into the air or absorbing into the wood fibers. Once enough water is gone, the polymer particles coalesce, coming together to form a single group, and the glue skins over, then hardens, bonding the wood pieces together.
Higher humidity slows that evaporation, since the surrounding air is already closer to saturation and has less capacity to pull moisture out of the glue film. Wetter wood also absorbs less water from the glue, since it has a lot of moisture in it already. Both effects slow the setting process, which stretches out open time.
The flip side matters more if you live in a low-humidity area. Low humidity, especially combined with wind or heated, dry shops in the winter, pulls water out fast and can cut open time down significantly on a big glue-up, sometimes catching people off guard on wide panel or tabletop glue-ups where you need the extra minutes to get everything clamped up. To combat a short working time, you can glue up in subassemblies.
Epoxy (West System and similar)
Epoxy is a different animal. It cures through a chemical reaction between resin and hardener, not by losing water. So humidity doesn’t drive the cure the way it does with PVA. What actually controls epoxy’s working time and open time is temperature, since heat speeds up the resin/hardener reaction and increases exotherm (the heat released from the chemical reaction). West System’s pot life numbers are all published against temperature, not humidity, for that reason.
Where humidity does show up with epoxy is amine blush, a waxy film that can form on the curing surface when certain hardeners react with moisture and CO2 in the air. That’s more of an issue in cold, damp conditions, and it affects surface finish and secondary bonding (you’ll want to clean it off before recoating), but it isn’t stretching your working or open time. If anything, high humidity combined with cool temps is more of a blush concern than a workability concern.
So the short version: PVA open time is humidity-driven because it’s an evaporation cure. Epoxy open time is temperature-driven because it’s a reaction cure, and humidity’s main mischief there is blush, not extended working time.
I’m the owner of Benham Design Concepts, a mixed media art studio where I design and build custom furniture and other works of art using wood, glass, stone, and various metals.
In this blog, I talk about the art I create, my journey, and the things I learn along the way.