I'm building a showerpan which will eventually be covered in ceramic tile. Based on advice from the folks at Home Depot, I installed the pre-pan, using fortified thinset mortar, laid over metal lathe. Now that it's in (and dry, I might add), I'm worried because rereading the how-to book I realize they recommend using a sand/mortar mixture. Do I have to tear out my work, or will the thinset mortar pre-pan be able to withstand compressive force?