If you are going over an existing ceiling, you may install the tongue and groove directly over the ... similar to how you would acclimate hardwood flooring. Add your stain or polyurethane before ...

This outline for how to lay cement board base under your tile floor is from a 2002 issue ... drywall screws spaced every 4 in. 3/4-in. tongue-and-groove plywood or OSB (oriented strand board).