If you just want ledges made with GS (which you CAN mold, after it has skinned, you should wait about ten to fifteen minutes after you spray it, just be gentle, otherwise you will completely flatten it out), You can either apply the GS directly to the glass, or you can apply it to a sheet of wax paper, let it cure, carve it, and then affix it to the wall with silicone. Check out my frog toad tank build log, you will see that I did several in that tank:
http://www.vivariumforum.com/communi...xperiment.html.
And postal, please don't think I am being rude, but Tiamat has already said (in another post you may not have read) that English is a second language for him, so please take that into consideration when you read his posts. It was probably that that made the post come off that way. I think his point was, yes you can use it, yes it can be molded, to a certain degree, and that you don't HAVE to do anything else with it, but you will want to, because it will look like crap in it's original, naked form. Correct me if I'm wrong, Tiamat.