First time poster. I just picked up a board with a blown out leash hole(through the fin box type) and am wanting to get it fixed up. I was thinking of plugging the hole from the bottom, stuffing it with solarez, sanding it smooth, drilling the hole to size, chamfering it, then sanding the edges smooth. Would this work or is there a better way?
Did it affect the fin box at all?
Nope. Fin box is perfectly fine.
If thats the case then I would think your way should work. I would add chopped glass to the resin you fill the hole with, and a layer or 2 of patch glass on top as well, feathered in.
Actually if it were me. I wouldn’t put it back there cuz I have never really liked those drill thru leash attachments, and you’ve just given me another reason not to like them 
But thats just me, & a different topic.
Your repair would work, but a leash plug install would be cleaner. The larger plug would cover more of the damaged area and look cleaner. Would be just as strong. A pice of cloth in the bottom of the hole would insure that no water would seep up into the foam. Also you would need to fill the hole in the fin box. Prefererably; use 1/32 milled fiber. If you use that for the whole smear, you will not need to use any cloth except to cover the plug at the deck.
Ummm, yeah, you have a pretty good plan.
I wouldn’t just use solarrez, or any plain filler. You can see where somebody did that once and it’s failed.Instead, I’d fill it, if you want to get cute use some sort of well-waxed tubing the OD of the hole as your plug well above the deck, sand the filler to the deck contour, then glass around it to prevent the sort of damage you see now. The filler alone, as you see, is kinda weak and kinda brittle. But I think you’ll have better results reinforcing the top surface with glass cloth.
Then pull the tube, chamfer lightly (you might try doing it by hand, using a sharp roundover router bit with a small pilot, in a tap wrench) , sand or polish very lightly and you’re there.
If you’re really really carefrul, you could fill, drill, chamfer, put more wax or whatever in the hole and then glass it and gently drill it again (see ‘tap wrench’ above) . That’d give you the best strength and durability. Watch out for resin filling the depression that is your chamfer. It’d be a tricky job, but that’s where the fun is
hope that’s of use
doc…