wrong cement backer width for wall tile?

i'm renovating my bathroom, and tiling my shower surround (i've installed a fiberglass tub). i've used 1/4" (I think technically it is 7/32) durock cement tile backer for the walls. when putting it up, i noticed that between the studs there was some give to the backer board when i applied pressure. i thought it was wierd at the time, but continued, assuming i had the correct material.

in a recent trip to my big box home store, i realized that there is also 1/2" backer board (somehow i missed this the first time when i bought the 1/4").

i'm assuming that it has less give, and is intended for use on walls, is that the case? if so, should I take down the 1/4" backer I put up, and replace it with 1/2"? i'm at a point where it would certainly be inconvenient (and a hit to the budget), but if its the right thing to do, i'll do it. i'm installing 6" ceramic tile over it.

also, i read in another post about a moisture barrier behind the tile backer. i didn't do that either. is that another reason to start over?

 

Yes, take down the 1/4" and yes you need a vapor retarder behind the 1/2" cement board to protect the studs from future water intrusions. The cement board is water resistant, it wont degrade or fall apart when exposed to water but it is not water proof, it will allow water to pass through the body of the board and soak the wood studs over time. Caulk in the corners and sealer on the grout will help in keeping water out also.

 

well, that's a bummer. live and learn i guess. does the vapor barrier need to be of any specific thickness? i used some for loose fill insulation on one of the exterior walls of the bathroom, could i just use the same stuff.

thanks much for the advice, glad i found out now.

 

15lb. roofing felt or 4or6 mill poly.