Sheet metal bottom or plywood. Cover with wax paper. Mold sides up with green masking tape. Mixture of resin and whatever, whatever being Qcel, pooldirt, sugar, Bearpaint polynonskid, baby diaper filler ala Herb…whatever. Shape to right size, bit just a little bit too small. 6oz Glass, hotcoat, spray with exact match to blend…gloss cot. polish. No problem, no brainer.
Or you could just fill it with clear resin…put a spider or penny in it…maybe a chicken bone, glass it over …boooo scary.
clean off the area and sand back towards the middle of the board a couple of inches top and bottom. 100 grit is ok.
use several layers of masking tape lapped over each other to form a shell for the filler u choose to use. microballoons and resin will work fine. i’d form it off the deck and then flip to fill from the bottom. the tape might sag a bit, but that will be ok. make sure the tape is tight and well reinforced. don’t cheap it. or it will leak. hmmm. how did i know that?
save a little it of the q cell mix before you catalyze it.
catalyze the rest and pour.
after its gelled but before it is rock solid, pull the tape. you can use a single edge razor blade to rough trim to desired shape. work the blade from the middle of the fill toward the outer edges. thin slices, don’t get anxious.
any voids or holes, use the saved q cell mixture to fill.
sand to shape.
i use 4 oz glass lapped about an inch onto the board top and bottom. sanding coat. sand.
for sealing you can krylon spray, or use a finish like mop and glo or a gloss coat and buff.
if you want that shiny look then when you final sand everything and you are sure it’s sealed and all, pour a dab of water on it and sand with like 400 grit and you’ll get a wetsand finish.