I have seen this on here before, but i have a question i haven't seen answered yet… I have a 1920's house, and i removed 3 layers of flooring and subflooring in my bathroom. i reached hardwood, with remnants of black tar paper on it, and this floor is level with the hardwood outside the bathroom. i have bought durock cement backer board, and plan on using this under the tile. a few questions first… 1) do i need to install some sort of plastic on top of the hardwood to protect against water damage? 2) do i need to remove the hardwood floor or tar residue or can durock go on top? 3) do i need to lay 3/8" mortar underneath durock or can i just screw it to hardwood? 4) do i need to tape/mortar the seams of the durock before laying mortar & tile? 5) does the durock need to lay perpendicular to the hardwood? (bathroom floor is only 4' x 7' so we're talking 3-4 sheets of durock max) 6) will 6" tiles be much less prone to cracking than 12" tiles? thanks for your help! these forums are absolutely great for diy-ers. thanks again!

What type of subfloor is required to support 12 in marble tiles? What do I check in the plywood and floor joists to ensure proper strength? If the floor an/or joist are not goo denough, how should I correct them?