butal is a water proofer,used under ceramic tiles,in wet or humid conditions,it may be sold in your area by roofers,look in the phone book under "waterproofing" and roofing supplies

Try spelling Butyl and do an internet search. Unless you have a moisture issue from under a slab, this should not be necessary. A quality tile and stone supplier can direct you to a compatible thinset for laying the tile, that is best for your specific application.