I have a debate going on regarding whether one should use cement backer board or waterproof drywall on the shower walls before installing the ceramic tile. What is most commonly used in the industry?

Looking forward to your answers :p

(Question moved from Introductions to more appropriate topic area to get more exposure to those who are best able to answer the question.)

I have always heard that backer board would be the most commonly used in the industry of redoing or building shower walls. But, that's not an absolute, because how you seal the tiles does make a difference too. I do have a story about shower walls though, if you would like to hear it?

I can help end the debate, greenboard is no longer used in wet areas but may be used on bathroom walls outside the shower. Wonderboard or Hardiebacker are now standard materials for under tile, same on floors. Clough, what's you story, I'd like to hear it.