Reconstructing the Floor
This is where it gets interesting.
Doing a new floor installation in a bathroom over a plywood sub floor can produce a really beautiful project., but there are details that have to be attended to if you want the result to come out perfect.
Earlier I talked about water and mold damage to the sub floor and how to repair that. So lets assume that the sub floor is all prepared, level, and solid.
Depending on what flooring material you’re going to use, you may want to consider first installing a thin cement underlayment or tile locker board.
Other underlaymenta board materials are available but cement board is unaffected by water or mold and is the wisest choice.
The argument for underlayment is that it provides a perfect flat surface for new flooring. However installation requires alot of careful measuring, of course there is a cost involved and your sub floor may be perfectly flat and undamaged, so there’s no need for it.
Depending on the new flooring you use, you may have some addition prep work on the underlayment.
Cement board screws will speed up the installation and they don’t rust. They are self tapping and have ridges under the head that helps them countersink. Sometimes its easier to just drill a shallow hole at each marked screw location so you’ll be sure they countersink.
If you are putting in sheet vinyl or vinyl tiles you need to fill each screw hole and all seams with leveling compound.
If tile is going in there’s no need for this. The mortar will fill in.
Here’s a couple of other things to keep in mind.
If you’re going to be installing tile. Stone tile, marble and granite, as well as other thicker tiles, in combination with the mortar and underlayment will elevate the level of the floor significantly.
The toilet waste pipe may need an extension for the flange (the ring around the pipe which the toilet bolts down to).
Additionally if you removed a sink vanity and tiled under it, the water supply lines may not fit if they are the rigid type. The same may be true for the toilet.
Another potential problem may be that the bathroom door may not fit and will need to cut something off the bottom. Finally the edge of the tile at the door may be higher than the flooring or carpet in the next room and may require a transition molding.
None of these are difficult problems, just be aware you may encounter them.