No you not have to put backer board behind the tub below the shower stall area. You only need to use it behind the walls of the shower stall.
Generally the tub is nailed to the studs and the backer board or sheetrock is put over the tub or just down to the top edge.
Cement board, at most contractor supply places it will be called DUROCK cement board or Permabase cement board. = =
Concrete backer board is usually used as an under layment for ceramic tile. It can be used on walls, floors or countertops. It has a solid core and is faced on both sides with fiberglass. It's an ideal under layment for wet areas like shower walls and bathtub surrounds, and is typically mold resitant.
Replace the drywall with tile backer.
Yes, you can.
If you are talking about a fiber cement backer board, the manufacturer of the board should provide the answer you are after. I am currently using Hardiplank to reside my house, and the manufacturer recommends attacheing the TyVek house wrap to the wood sheathing per TyVeks recommended process. Hope this helps.
Old floorboards tend to cap and move; being individual boards. Putting down a backer board gives you stronger/flatter stable floor.
Pull it off with pliers if that's easy. If not, cut out the backer board and renew it. It should be done when new tiles are done anyway. Use a fibre or concrete backer board, NOT wallboard.
15
Not usually, no. As long as the sub floor is solid, without water damage, etc then a backer board is usually plenty. You need to have 1 1/4" of sub floor and backer board when you put the tile down. Generally speaking, homes are built with at least a 3/4" sub floor and 1/4" cement backer board with 1/4" x 1/4" trowel of thinset equals this. If you are not sure, don't assume. Find a vent in the floor. Pull out the register vent and use a hand mirror to see the sub floor. Take a tape measure and measure its thickness.
No, it is not...it causes "tear out" or splintering. There are, however, numerous methods for avoiding this problem, or at least keeping tear out to a minimum. One can score the plywood first by setting the height of the blade just deep enough to score the top veneer, then recut all the way through. One can use a backer-board and set the saw blade deep enough to cut into said backer-board. One can also use tape. It works similarly to the above-mentioned backer-board to prevent tear out. Of course, there are others, but these three just came to mind. In fact, I used the backer-board method several times just today (I am a carpenter :).
Yes on wood, no on smooth solid concrete