I would like to install ceramic tile over an existing oak floor. I am told I need to first put down a backerboard so the mortar doesnt get into the wood and cause rotting. The backerboard is used as a moisture barrier. Can I use something thinner, like a vinyl or paper moisture barrier, or a paint on moisture barrier such as shellac or Thompsons water seal, or a thin coat of floor leveller to use as a moisture barrier? Actually the floor leveller is a cement product so may not be a good moisture barrier. Any suggestions?