I have a stripped polyurethane board that was pretty rotten, mostly around the fins and tail. I was able to remove the worst of it, but I'm wondering how to fill the voids left over. What's a good foam filler for the voids, Especially the voids where the fin boxes would go. There are a lot of options I keep finding and I'm not sure which to trust most. I've been looking at Qcell, microballoons, and Totalboat Silica Thickener. I'm also considering cutting and fitting polyurathane foam itself and gluing them into the holes. also I've seen a lot of guys coat blanks in drywall spackle and things like that, what are the benefits of that and what makes it "necessary".
Also I have some polyurathane pourfoam left over from a boat I just built, Could I use this to secure the fin box voids?