Prep for tiling
My sunroom has 6 x 6 tiles which I want to replace. I pulled up a couple and dicovered that they have been installed on top of plywood 1/2 inch. There is a basement beneath the sunroom.I want to install larger tiles 18x 18. My question is how to prep the floor. The tiles seem to come up fairly easy but the glue is stuck to the floor in some cases. Do I need to scrape off all the glue? Can I tile on the plywood or should I install backerboard?? How thick backer? 1/4 or 1/2?