Drilling a foil board

Apologies for the newbie question, but I’d prefer to look like an idiot than wreck my board.

I’ve got a Slingshot Alien Air board cheaply, which has adjustable tracks in place. I’d like to drill a reasonable (~15-20mm) wide hole between the two tracks to run the wires up from the mast in. The issue is I’m not sure what to fill it with to protect the board once I’ve drilled it. Is there a specific resin? All fibreglass resins OK?

I’ll be epoxy’ing the wires in place in the mast both top and bottom to protect from water. I’ll also be using adhesive leash mounts to secure the top battery box in place temporarily.

Great that you’re asking. No sense messing up a great board.

Use an epoxy. Resin Research makes great surf resin for this kind of thing but any surfboard shaping supply will have 2 part surfboard epoxy.

Be careful, first don’t ever use polyurethane resins for EPS foam boards. Most SUPs and Kiteboards will use EPS. Poly resin will melt the EPS. Just stick to epoxy, much safer and it works on all kinds of foam safely.

Also, don’t ever pour more than say 1/4" of resin into a space as it heats up when it sets and will melt the EPS. So pour it in stages. Also mixing in Cabosil or glass micro balloons will slow the exothermic reaction and reduce heat.

A lot of folks in board building drill out a larger hole than they need, fill it with epoxy and micro balloons mixed and then drill out a smaller hole so that there’s no exposed foam to collect water. EPS foam sucks water in and is hard to dry so be careful to not let any water into your board or a few weeks in you’ll have a 100 lb board. :wink: a lot of surfers weigh their board before they start surfing it and write it down somewhere. That way you can always tell if it’s leaking and taking on water.

Experiment on some packing foam first and get a feel for things before you tear up a good board. Composites are not that hard to work with but they can punish the casual user. Test, play around a bit, and then work on your board. And wear a dust mask at least if you’re drilling or cutting fiberglass. Tiny glass fibers are not good for lungs.

And NO ACETONE to cleanup epoxy. It can make you sensitive and have a reaction so that you can never be around epoxy again. Clean up with white vinegar or denatured alcohol or orange hand cleaner works too.

Good luck, this stuff is truly fun.


Just noticed the hole size you’re mentioning. That’s pretty big to fill with resin if your board is thick. For that you might consider getting a section of fiberglass or carbon tube and epoxying that into place instead. Might be less trouble but if you do, do t just epoxy it, put some fiberglass cloth to seal in each end and do a proper surfboard style ding repair where you glass, and then put another layer of epoxy over it. Watch some surfboard repair videos for more info.

Great advice and idea using conduit. I’ve just noticed in looking at PM’s old videos that he also implemented this idea.

We’ll see how we go, resin ordered!