HGTV's Mike Holmes suggests carrying out this step properly before embarking on your bathroom renovation to save you time, ...

Position the backer board so that there is a slight gap, about ¼ inch, above the bathtub. This will eliminate capillary action where the water is drawn up behind it.

Cement Board. Cement board is the most common and widely-known backer board. Cement board is readily available and relatively inexpensive (about $10 for a 3 x 5-ft. sheet). The 30-in. x 5-ft. and ...