[NNess]

Our bathtub was finished w/greenboard (sheetrock) around it and we are wanting to tile, can we place cement backer board directly over the greenboard and then tile or do we need to tear out the sheetrock and place the cement board up?

[mtconc]

What kind of sheetrock is it?how long has it been up? What condition is it in? Most importantly,why do you not want to remove it?

[NNess]

what kind of sheetrock is it?how long has it been up? what condition is it in? most importantly,why do you not want to remove it?

Not sure what you mean by what kind. It is green, maybe 5/8 inch. It has been up for maybe 4 years. Good condition, primed and painted. It would be easier to not have to take it down but to just add cement board overtop of it. The thickness of the sheetrock and cement board are different so if we take it down it will not match up next to the sheetrock where they meet on the wall.

[mtconc]

Green is moisture resistant,not as good in a wet area as cement board. My guess is the cement board is the same thickness as the sheetrock. If water gets behind there,the tiles will fail on sheetrock.I would suggest sheetrock gets replaced.

[leifweaver]

No, the cement board and MR sheetrock will form a sandwich that will allow a film of moisture and lead to mould. Best practice would be to tear out the greenboard and replace with the cement board. You can use furring strips to bring out the cement board so that the tile will work with the adjacent wall material, if needed, or use hide the transition with trim (it works best if the tile is proud to the adjacent surface). However, there is a product called Kerdi that you can use over the greenboard and seal it from the moisture, and then tile directly over the sealed greenboard. You will want to take extra care sealing at the tub flange. I have used this product many times, and have never had a problem with it. Properly installed, it will last indefinitely.