I've seem a lot of people telling that greenboard drywall SHOULD NOT be used in bathroom and wet areas. However, in Brazil (where drywall is kind of a novelty yet) the manufactures recommend greenboard for bathrooms and describe treatments to make it safe to use (even with tiles), not only that, but cement board is very difficult to come by here.
Basically, it says that the junction between the wall and the floor must be waterproof treated up to at least one feet up the floor (using various methods). Shower areas should be completely waterproof using the same technique, and after that you can install tiles using a flexible grout and mortar on top of the waterproofed drywall.
My question now is: is it safe to use greenboard if done in that (correct!?) way?
Best Answer
Green board is basically sheetrock with a waxy paper face. It's not as stiff as cement board, nor as waterproof, both of which are nice to have when applying tile.
CAN you use it? Sure. It's been done before. Is it to code? Not sure. You'd have to check with your local authorities.
If you decide to use it, see if you can find a product called 'redgard'. It's a paint-on waterproofer that should help keep the green board dry.