Anatomy of a Tub Surround Built to Last
1] Start with an unfinished bathroom.
2] Tear out the old drywall down to the bare framing studs. Add in additional new lumber where needed so there is no flexing in the wall.
3] Fur the studs out even with the lip on the tub, staple a roofing felt or polyethylene moisture barrier to the studs.
4] Sheet with cement board. Tape and mortar the seams. Plenty of cement board screws. Use polymer enhanced mortar on tub surrounds.
Finished bathroom with a 100 year porcelain tile floor and tub surround.