Humidity and Hotcoating Question

It’s time to hotcoat my first board, but I’m scared of doing it in such hot and humid South Florida weather–like 85 degrees/ 59% humidity. The polyester resin I have already has the styrene mixed in it. The bottle says to add 5 drops of MEKP per 1 oz. of resin in temps over 85 degrees. I’m worried about it curing poorly with the high humidity and heat. Can anyone give me any first hand experience and advice with this issue? I searched the archives, but never really found a good write up. Seems weird; maybe I used the wrong keywords.


Zander M

Try a small test batch maybe…try to make sure the temperature is stable,no rapid increases or decreases.If your using poly the temperature increase won’t be as big of an issue(eps outgasses and causes pinair,little bubbles all over the fill coat).

Thanks Jesus. It’s no good today anyways as there’s a bunch of thunderstorms on their way. This weather thing for backyard glassers is a real pain in the ass. I’m just imagining my perfect controlled shaping shack… some day.

You really shouldn’t have a problem with the temp or humidity, it’s not perfect conditions but there’s thousands of boards, boats, and everything else made with poly resins in the Florida summers. It sounds like you have the Silmar pre-mixed hotcoat resin, but if not be absolutely sure your resin has both styrene and wax added. The additive is commonly called ‘‘surfacing agent’’. And put the ‘‘hot’’ in hotcoat, you want to catalyze it enough that you have time to brush it out quickly, let the wax rise, and not much else. UV cure makes this a little less risky for the inexperienced, next time you might want to try that.

Thanks Mike. I just finished hotcoating the top. I tested about an ounce on a plank of wood. It set up and sanded fine. So far so good. How can you tell if the wax is rising to the surface?

You should be able to see it as sort of a film on top of your hotcoat, after it’s brushed out and sits for a minute or two. A pattern in this film will show your last brush strokes. Kick it too fast, brush too long, or forget to add SA, and the surface will stay gummy and unsandable. Another way to ‘‘see’’ it rise would be to pour a little uncatalyzed resin in a cup and watch it as it sits. Then just pour it back in your storage container. That’s also the way to tell if your ‘‘premix’’ actually has SA.

Uh oh. I’m not really seeing a film on the surface, but it isn’t tacky or gummy. It looks completely sandable, but it’s glossy. Is this normal? When I hear the whole film thing, it makes me imagine the coat rough. I got the stuff from Surf Source. It is called Ding All Sanding Resin. I assumed it had the surfacing agent in it, because they also sell laminating resin. The bottom of the board where the resin kind of built up is still tacky. I must not have used enough MEKP. I followed the mixing guidelines on the back of the container.

Don’t worry, it’s likely just fine. You’ll find out when you sand. That resin DOES have wax and styrene added.


the problems start with cold weather + humidity (less than 16C, more than 75%H)

and that is not your case

Thanks for the help. The deck set up and it’s definitely sandable. Another step closer to finishing this thing. I just have to order some more sanding resin, and coat the bottom. Then the fin and hopefully some waves.

Zanderm, you should check out Glue Products on Forest Hills Blvd in West Palm. They sell pretty much every thing you need to glass a surfboard including suncure resins. This way you don’t have to wait and there is no shipping cost. Just type glue products in google and their web site will come up.

Hope,the rest of your glassing went well

Thanks. i will check them out next time I’m in town. I’ve been building this board at my dad’s house in Fort Myers so I’ve had to order anyways. I order from Surf Source. They always ship same day, and I always get it the next day. I go to school in Boca and have nowhere to shape over there.