Getting epoxy smooth in hot weather

I also posted the following on the MAS website:

Is there a technique for getting the epoxy on smooth in hotter weather?  When it gets above 85 or so the epoxy starts to cure before I can get it "tipped off."  Using Low Viscosity Resin 30-002 and SLOW Non-blushing Hardener 30-008.

I would also add that in trying to smooth it out I am often sanding back down to the wood.  A vicious cycle.

5 replies:

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RE: Getting epoxy smooth in hot weather

First, stop sanding before you get into the wood. Instead of trying to level it by bringing the high spots completely down, fill in the low spots. That is, sand until you're almost, but not quite into the wood. You should have dull and shiny areas left. The shiny ones are the low spots. Add another layer of epoxy and sand again. You should now have more dull and fewer shiny areas. Repeat until it's all dull.

Use thinner coats of epoxy. Apply them with a low nap roller. If you already are, don't load up the roller as much. If that doesn't help, use a squeegee instead.

Mix smaller batches, 3 oz or so. Smaller batches take less time to apply so they won't start curing in the pot before you're done applying them. The also take longer to go exothermic.

Mix the batch and pour it onto a polyethylene sheet to load your roller. This increases the surface area to volume ratio (as do smaller batches) which allows the epoxy to dump the heat of reaction faster which keeps the epoxy cooler which keeps it from curing as quickly.

Store the epoxy in a cool area until ready to use (basement, air-conditioned room, etc.) and only bring enough out to the shop for the current work session.

Cool the hardener in an ice bath before using it (not the resin because it'll form crystals).

Work first thing in the morning, before sunrise if you can handle that.

And if all that fails, wait til Fall.

Good luck,


RE: Getting epoxy smooth in hot weather

I built my Skerry in southwest Florida and part of the epoxy work was accomplished in the summer time, so I know what hot is about. I was having problems with the epoxy, even though tipped out, cured with an alligator like, or wet glass, surface. I fount the trick to a smooth finish is first and foremost, use thin coats of epoxy. Very thin coats. Now you can't do that when you epoxy cloth because you're trying to fill the weave but when coating bare wood, I used a squeegee to make the coat just barely wet the surface. If you continue to squeegee on coats of epoxy before the previous is fully cured you will still get the chemical bond and can make it as thick as you want. Keep in mind though that the epoxy coat on the bare wood adds little strength, so just enough to seal the surface is really all that is necessary.


RE: Getting epoxy smooth in hot weather

I heat my shop to 85 degrees prior to using epoxy for seal coats or glassing.  I can completly coat the boat and then return to the begining to level the epoxy by using an auto body soft plastic squeegie. The main problem I always have is that it takes so long to set up to a viscosity that is hard enough that I do not remove too much epoxy.  

I do not tip off epoxy very often, usually only when applying a seal coat to bare wood.  I use a heat gun to get rid of any bubbles and it has always worked well.  

I would not sand too much or risk cutting into glass or into the wood as that could cause cosmetic discolorations of both glass and wood.  

Take a look at my blog on and you can see pics of my latest build using these methods.

Robert, Visionary


RE: Getting epoxy smooth in hot weather

Thanks to Lazlo, "wing," and Robert for your help.  I was sanding too deeply because I didn't want to leave any shiny areas.  Also, I was using a roller which was laying the epoxy on a little too thick.

I tried putting on a very thin coat using a foam brush and this works well for me.  Got a nice smooth coat on the Skerry rails and breasthooks.  A light sanding and one more coat should do it.

Later I'll sand the hull interior and exterior and apply very thin coats, but I'm not as concerned about getting the surfaces totally smooth, except on the seats, which will be bright-finished, same as rails and breasthooks.  Everything else will be painted.

Thanks again.  This has saved my "bacon." 

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