Surfboard repair

[Tele 'til You're Smelly]

I have an old big SUP that is going out to pasture as a flatwater board. It has a broken booster fin box, and it's not worth paying for professional repair (not that there's anyone around here who could do it)- and I won't need booster fins anymore, and just want to fill the boxes and the cracks & gaps that go into the board. What can I just squirt in there and then smooth over the bottom that won't melt the foam core? I've made that mistake before . . .

[Matt J]

Polyester resin?

Depends on the material of the board. If it's epoxy I'd use an epoxy resin and if it's polyester I'd use that.

[Quadzilla]

Done plenty of fin box R&R's as well as filling voids. I would take a router and route out the plastic boxes. you should end up with a rectangular void with the box gone. Then glue a piece of styrofoam in the void cut to the same dims as the void. You don't need a lot of glue to glue it in so there shouldn't be enough heat to melt anything. When the piece is glued in there should be a little of styro above the void and you sand it level. Then glass over the filled voids with a couple of layers of glass, followed by flow coat of resin, paint and call it good. You need to use epoxy resin for the glue, glassing and flow coat.

[Tele 'til You're Smelly]

ok so it's a fiberglass board- but my recollection is that "fiberglass resin" (is that polyester resin?) melts Styrofoam- so should I use epoxy resin regardless?

[Quadzilla]

ok so it's a fiberglass board- but my recollection is that "fiberglass resin" (is that polyester resin?) melts Styrofoam- so should I use epoxy resin regardless?

All modern boards including SUPs windsurfers et et are fiberglass over foam blank and made with epoxy resin. The reason they use epoxy is so they can use a lighter core like styro and keep total weight of the board low. Epoxy can melt styro too that is why you should use a thickening agent like microbaloons to help dissapate the heat and never use a large qualtity of resin in a void but fill with foam pieces glued in to fill void with small amount of resin. Saves $$ too. Anyway, use Epoxy.

[Tele 'til You're Smelly]

Thanks. The other thing that's coming back to me from my windsurfing board repair days was to use expandable insulation for voids you don't want to cut all the way into, coat the surface that you'll glass over with Elmers (which won't melt anything), and then glass (or I guess epoxy) over that for finish waterproof coat. Hillbilly for sure, but I think this work too? I know I'd bugger up cutting out the fin boxes.