any general slow setting 2 part liquid epoxy should be fine. you can just get it at a hardware store. what you want to do is put a thin layer over the exposed core. this seals the core of the ski so even if the ptex falls out the core doesnt get exposed to any snow/water. as the epoxy begins to set up take a razor and kind of cross hatch the surface to roughen it up to give the ptex something to hold onto. after the epoxy completely cures you can then drip in the ptex. (i use the black toko) i found that using a butane torch to light the candle really cuts down on any carbon forming which may weaken the fill. put the ptex in using layers letting each "coat" solidify untill it is still warm and goey but not liquid and definitely not entirely solid before putting on another coat. if you put it all in at once it will crack up and fall out much quicker. build up the ptex untill its above the base of the ski then with the last layer take a steel scraper and press it into the ski. if you layered the ptex waiting just enough time in between each layer the bottom will still be soft and goey and pushing it in really helps it hold. then just scrape off the excess with a really sharp lexan scraper or steel scraper, brush it, buff it, wax, and ski.
the biggest part to getting a good ptex fill is layering it while its in that goey stage. dont let it cool all the way but dont let it just pool up in a big puddle.
