I WANT TO INSTALL 18" CERMIC TILE ON 700 SQ. FT OF FLOORING, THIS IS A OPEN CONCEPT, I TALKED TO CONTRACTORS AND I'AM GETTING MIXED INFO., I WAS TOLD I COULD LAY 1/2" PLYWOOD ON MY 5/8" FLOOR AND THIS WOULD BE A GOOD SUB FLOOR?? I NEED TO KNOW IF THIS WOULD WORK, MY OTHER PROBLEM IS I WENT WAY OVER COST! ON THIS TOTAL RENO.