I am having a new shower built in my bathroom and my contractor is using Hardie board without a membrane. The shower is going to have tile installed over the Hardie board with thin set. Shouldn't he be using the membrane too to make it water tight?
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Season 38, Episode 26
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CBU is not waterproof, I'd stretch 6mm plastic on the walls before I hang it.
A pvc membrane should be used on a shower floor when a mud base is used. For walls, tarpaper or heavy plastic sheeting is fine. It needs to overlap the pan liner. A shower pan can't be made with CBU because there would not be any slope. A special drain fitting with weep holes is also employed to allow water that permeates the mud bed a way to drain.
For reasons like that, we have switched over to Schluter system shower pans, they have built-in slope, and you tile after swaddling the whole shower surround in Kerdi membrane, which is applied right over the drywall using thinset.
Casey
What they said plus,
All ceeement board manufacturers require the seams to be taped and floated.
IMHO a surface membrane such as kerdi is superior to sheeting behind the ceement board especially if there is a bench or niche involved.
The way you describe things is a future failure waiting to happen. Tile installations are not waterproof in and of themselves. Thus the use of membranes, being a more modern and better way than using poly to waterproof, is what we do here because done properly they cannot leak ever period.
I like doing jobs that never require warranty work!
Phil
I forgot to state that you want a mud pre-slope underneath the PVC liner so the weep holes work and the mud bed stays as dry as possible. Without the pre-slope things tend to get wet and stay wet, which means that a stone tile floor turns darker and looks water-logged, which it is.
Casey
don"t let him do it, i have repaired many of these handy man showers. get a license contractor to give a price with a membrane, and a guarantee.
You either use a rubber membrane between the preslope and the final tiling slope. (old school) or you use a SAM...Surface Applied Membrane such as Kerdi or Hydroban over ONE slope. The advantage being that water NEVER penetrates beyond the barrier, thus dries out quicker.
Look at it this way~the waterproofing goes on FIRST! The tile and grout are only there to make it look pretty....they have absolutely NOTHING to do with the waterproofing.