Hardie board for new bathroom

Question

Hi Team

I am planning for a new bathroom which will be framed, roofed, floored and wether board cladding by a builder. i choose to finish the internal.

1.I am planning on 6mm villaboard lining on the internal studs for wall. insulate with batts

2. 6mm ceramic tile James hardie underlay on top of particle or plywood subfloor

3. i would double up to raise the entire floor and so i can create a slop in the walk in bathroom by screeding  down towards the drain

4 tiling all floor area and walls up to the ceiling

the questions are

1. do i need water proofing. is it on or under the cement board. i could not find a instruction or video to waterproof or not to on a cement board when used as bathroom floor or under tiled shower area

2. is the thickness of the board appropriate for the wall or do i need a some kind of backer board

JDE · Accepted Answer

Sankara

Yes you definitely need a waterproof membrane. It goes over the cement sheeting under the tiles. If you are getting the job signed off by council you need the waterproofing done by a professional (denfinitely where I live so check). If not after sheeting the bathroom you will need to prime your sheets ( something like Dunlop Multipurpose Water based Primer) some tape for corners and joints, and waterproofing membrane (Dunlop Undertile Waterproofing) it comes in a bucket and you paint it on. Bunnings has the mentioned products and the equivalent in a couple of other brand its not cheap about $230 for a 15l bucket. Make sure you put on the minimum 2 coats with stroke direction at right angles between coats and double that on corners. There is a video on waterproofing a bathroom on the Bunnings how to website.

Re the thickness check Mitchell's response to question "Villaboard for wet areas 1/4" or 3/8"? For a full answer  His answer was yes unless you are using really heavy tiles. 6mm is what I used when creating an ensuite in my wifes studio. The mentioned products are just the ones we used. JDE