I have used it to make a 15mm canal. You can pour it out (not too thick) to fill an area and just wait for it to dry. It does shrink some, which left water a couple mm up on the sides of the canal. It leaves a slight rubbery texture to it, which makes brushing off any dust/flock a pain, but minor. I have not poured multiple layers, but it says you can. Pretty easy stuff to work with. It has a long shelf life once opened.
Currently this is the closest picture of my canal I have online:
http://s190.photobucket.com/albums/z18/Schlesie...