i just finished my hotcoat (on my first board) on the bottom. to make the crisp edges on the rails by the fins, i used tape to make walls to build up the resin. because of tape and the tail rocker, a lot of resin build up in the tail and it cured super thick. i had to use a grinder to get rid of most of the build up. i was discouraged to find that i sanded (or ground) through the glass and had a ding in the tail before it even left my shop.when i cut out the ding, i realized why i sanded through. the hotcoat burned the eps foam in the tail. it was completely hollow underneath the glass.
so my question is why did it do this?
did i add too much add. f?
was it because of the the build up of resin in one spot?
i think it might have been the build up because it was smoking in the tail when it started to cure. i just figured it was burning the tape. i had done a big ding on my longboard and filled it in with a lot of resin, however that was with 1cc of add. f. per ounce on hardener instead of the hotcoat (2cc per ounce) i think it might have been a combination of the two.
Hrmm… hollow?? Sounds like styrene damage… are you sure you didn’t accidently have some styrene monomer in the area? I’ve never had resin hollow out the board, I’ve seen it melt but then it wasn’t hollow, everything sagged in the cavity…
there was a little bit of foam still intact at the bottom (where the deck part of the tail is) but the rest was completely burned out, from stringer to rail, tip of the tail to about 4 inches a way. there was a few eps particles sitting there, they were about 1/4 the size as usual. it was really strange. i had to fill the whole thing with resin (which then smoked a little bit again)
It’s been my experience that when working with epoxy and leaving a pool of the stuff any deeper than 1/16" thick is asking for trouble. There’s a fancy word for it – something like exothermic reaction – but the bottom line is if you have a little lake of the stuff it’s gonna heat up and accelerate it’s own curing time exponentially. The hotter it gets the faster it goes and the faster it goes the hotter it gets. It’ll just bubble up into a hot smoking froth if you leave a little in a small cup about 1/2" to 3/4" deep.
So get the stuff out of the pot quickly and get it spread out. Then ir’ll cure nice and evenly and not go off smokin’ and cook the surroundings.
I had the same thing happen installing a fin box. I had too much space around the box, so voila, the foam certainly does melt. I cut the glass off over the entire area that was melted, then I used epoxy to glue in new pieces of eps that fit snugly. I screwed up again and melted that foam as I sanded it down flush with the surrounding lam. Watch the heat! I redid the patch and sanded more carefully, but I forgot to tape off the area around the patch, leaving myself way too much extra cleanup. But it worked! I then put a final laminated tail patch over the entire area. I forgot to add tint to that, so it does not look very pretty. I basically panicked after the initial melt-out.
Fin box installation with epoxy is tricky business. I’ve had good with wraping a center fin box with three layers of glass so that the process handles much like board lamination. The glass fills the cavity and so there isn’t much pooling. for rail fin boxes mixing qcell with the epoxy and making a thick paste to set the boxes with seems to moderate the exothermo process. I like to color the foam of my epoxy laminated boards so I mix color into the paste and use the same stuff I use to baste my board with. It’s worked pretty well up to now.
Guys, I’ve had a thunk about it… You guys using RR right? Now I’ve yet to try this magic grape jelly but what I do know is that many people are using the “fast” hardener, this may not be a good idea if heat buildup is your problem. I personally have used generic epoxies, fast and slow. The fast ones get hot, I assume the RR is no different. Nowadays I use Resoltech from the Atua crew, slow hardeners, I get 45 minute pot life on average and next to no exotherm.
