You could use an epoxy,But if your just filling cracks I would
use A automobile car bondo.It smooths down when wet.It is easy
to sand when dried.I used A bond from A model shop but I was
paying way to much.After reading about bondo on TDH I tried
it and it works wonderfull.It is pretty much the same product
except you can get A large can at wal-mart for about $15.00
This can will do several costumes.