When installing cement backer board, is it necessary to put down some thin set mortar and then lay the board and screw in place, or can I do without the thin set?
You do not need thin set. Just screw it in place.
If you want to do it right I would apply the thin set and use the screws.
Backerboard is used to stiffen the wood subfloor when you lay tile. This is important so the subfloor doesn't deflect when additional weight is put onto it (thus, breaking the tiles). Since you have a cement floor, putting down a backerboard wouldn't make any sense, but the floor does need to be level. You can pick up self-leveling compound at the hardware store. It's going to be in the same aisle as grouts, tools, etc.
When doing a cement board you MUST apply a filler .. This is thin set . This provides that there are no gaps or weak spots between the cement board and your subflooring. All you need to do this is a 1/4 x 1/4 square notched trowel. I will spread the thin set and put in a pre cut or whole pc and walk on the pc to make sure it s embedded into the thin set. Some people will say construction adhesive, but this will still allow gaps. ATC and TCA tile hand book guide lines call for a FULL spread in between the sub floor and cement board. Then using a minimum 1 1/2 inch galvanized roofing nails or screws to put down the board with. This is done 8 inches in the field and no less than 6 inches along the seams ( I do 3/4 inches) Any other questions you can e mail me thru my avatar and check my qualifications there GL
