hey, i use this stuff called plastic padding, it's got a yellow package, it is basically same stuff as everything else, comes in 2 parts, the cementy/mankstuff and then the hardener, u mix em up at about er... 5 parts cement to 1 part hardener, or somthing like that, depends how quick you want it to dry up heh. then before it hardens, whack it on ya model, then after about 15 mins ish or when ever u sand and smooth it out
it's okish for cracks, exept sometimes the edges turn up if it hasnt gotten onto the model enough and flakes off when you are smoothing out. also it's not the best for scribing either heh, thinking about it actually i might stop using it and find something else hehe
-Tage