: I used the dam method ... easy and works fine. Before the deck and
: hull are attached

In doing end pours on the VOLKSKAYAK, we do them after the hull and deck are joined - think it ties it all together really well. I've used both straight and mixed epoxy - gotta cool the end, or the stuff will boil from the heat generated by the exothermic reaction in a confined space, and you'll end up with an end pour that looks like sponge toffee. I now plastic wrap and tape the bow or stern, then stand the kayak bow/stern in a bucket of ice and let it chill for about 15 minutes before pouring. You can also do several small pours.

For my money, pretty well any thickener - silica, microballoon, wood flour - works for an epoxy end pour - you aren't looking for any special adhesive performance, just to build up bulk to fill up a space. HINT - If you do get a little bit of heat going, and see wisps of 'smoke' coming out thru the hatch, resist the instinctive reaction of sniffing the smoke to see what it is - don't ask me how I know...;-