Three Golden Rules of Epoxy Resin
It looks like glassing your boards with epoxy resin has become the more popular choice over polyester resin based on our sales records this year. 2-3 years ago we’ve had plenty of experienced poly guys come into the shop stating they’ll never use epoxy for one reason or another. Today most of them have added epoxy to their skill set and some of them now say “I’ll never use polyester resin again! It stinks, it’s weak, it’s hazardous… epoxy’s so much nicer to work with.”
Notice I used the words skill set to describe the act of using epoxy. Skill comes from knowledge and experience. So here’s a little more epoxy knowledge to help elevate your epoxy experience.
For years I’ve been telling people this little anecdote about epoxy to help them understand the importance of measuring epoxy thoroughly:
“The resin and hardener molecules are like a mingling at a party in the mixing cup. You want everyone to hold hands, that is where the strength is (this is called cross-linking). Anyone who is not paired up is floating in there, useless, in the way, and causes a soft spot in the cure. So an accurate mix ratio is critical so everyone is holding hands and there are no extra stragglers screwing up a fun party”
The epoxy systems we sell, Greenlight Marine Grade Epoxy and Resin Research are both measured and mixed at a 2 parts Resin to 1 part Hardener mix ratio by volume (in a graduated bucket).
But to be most accurate and have a full, durable cure to the epoxy it is best to weight the components out with a digital scale.
Greenlight has used and evaluated many different types of digital scales over the past 10 years and now offers two of the most accurate, reliable, and affordable digital scales on the market.
- The Golden Rule of Epoxy #2 : MIX Epoxy Resin THOROUGHLY
Now that you have all the epoxy molecules measured out precisely, it is important to mix the resin thoroughly so all the party-goers get to mingle and find a partner to join hands with.
We recommend slowly mixing the resin for at least 1 minute and be sure to scrape the sides, corners, and bottom of the mixing bucket to pull the viscous resin off the walls.
We’ve received far too many emails with first time epoxy users saying they have a soft spot on the board or “it didn’t cure”. This is usually from bad mixing habits and the resin stuck to the sides and bottom of the container has not cross-linked with the hardener molecules!
EPOXY Seal coats:
Best tip we can give for a flat and smooth epoxy seal coat is to lay it down and walk away! Don’t screw with it! Let it flow out and lay flat over time.
Few things I can tell you about seal coating technique.
- Mix the resin slowly and do not dip the mixing stick in and out of the resin, this will introduce air into the resin and make it a little cloudy. Same thing happens when you “whip” the epoxy up. We want to keep the air out for the least amount of bubbles.
- Another way air gets trapped in seal coats is by plowing the resin too much. Notice how when the epoxy rolls over itself how it tends to froth up? Avoid that. Just lay a fat bead of resin down the center of the board and plow it out with one stroke them move to one side and continue to plow it out towards the rails, while adding more fat resin beads as needed. Try not to let the brush go over the same spot twice.
- Cross stroke gently, it’s just helping to even out the resin distribution on the board, keep as much resin on there as possible.
- Walk out or “tip out” even lighter than the cross strokes. Just let the weight of the brush level out the cross stroke marks and wipe the resin off the brush into the mixing bucket after every stroke.
- THEN WALK AWAY! You’re done for now! (See Golden Rule #3)
- About 10-15 minutes later come back and check it out for anything funky going on like pin holes, fish eyes, or separations on the seal coat.
I just glassed a wake surf board outside in the worst conditions, didn’t blow the lamination off, just a quick brush off to see how bad the fisheye and pinhole situation would be (and also an opportunity to figure out the best fix for seal coat problems). I followed the instructions I wrote above and guess what? Only 2 small issues after 10 minutes of the resin flowing out and settling (other than a couple bugs landing on the board but that gives it character).
I had 2 fish eyes (separations) so I simply dipped a gloved finger into the mixing bucket (resin is still flowable and not hardened) and gently swirled it on the separated area. It connected with the existing seal coat and filled the void and still had time to flatten and bond.
Separations in the seal coat is a epoxy surface tension issue. I just put a little resin where it needed to be to fix the issue.
So I guess the GOLDEN RULE of Epoxy #3 is:
Walk away, then come back and fix any little issues
Also, not a golden rule but a great tip: Pull your masking tape after the resin has tacked up (45 mins - 1.5 hour depending on temperature)
This will eliminate the masking tape from getting trapped under the resin and having it tear into a lot of piece to pick off the board.
It’s OK to leave the tape on the board after the seal coat has cured if time doesn’t permit pulling that tape earlier. Just use a razor tool to scrape the tape off the board, it’s much easier than picking it off.