Hardie Backer Board Or Plywood Substrate + Homelux Membrane

[DazJWood]

I realise there's lots of info already on these forums concerning the questions I'm about to ask, so please excuse me asking them again. My post is really just to summarise what I plan doing and see if I am definitely applying the right materials and techniques. You'll have to excuse my naivety to all this as I'm not an experienced DIYer by any means! But I'm trying

I am in the process of doing my bathroom. (Actually I have been since February but that's another story ). I have bought marble floor tiles and the plan was to lay these on a plywood base. The floorboards currently in the bathroom are of the 18mm chipboard variety but unfortunately a number of them are water damaged. The one under the bath was completely sodden so I have already ripped that one out. After researching this forum and a number of others on the net I had come to the conclusion that the ideal solution would be to take up all the chipboard flooring and replace this with WBP 22mm plywood and tile over the top.

I am now wondering about the use of Hardie Backer board. I've read through their leaflet and this seems like another ideal solution. I could replace the damaged chipboard flooring with the same and then go over the top with hardie backer board.

The hardie cement board is only 6mm thick. Is this a sufficient thickness to tile over to avoid movement?

There are obviously numerous options of which I see them as being the following:

1) Should I remove existing chipboarding completely and then replace with 22mm ply and tile over.

2) Remove existing chipboard floorboard, replace with 18mm WBP ply and then fit hardie 6mm backerboards and then tile over.

3) Leave good chipboarding and replace water damaged ones with the same new ones. Then fit Hardie 6mm backer board and tile over.

4) Then I guess there is all of the above with the addition of a Homelux membrane (or similar product).

While I'm on the subject of Hardie backer board and Homelux membrane: I was planning on using the Homelux matting onto plasterboard for my shower cubicle. Would I be better using Hardie backerboard (instead of plasterboard. One wall currently has no boarding at all and the other with plasterboard will need removing for pipework anyways) and then Homelux membrane over the top for this application as well? Is that overkill?

Thanks in advance,

Daz

PS. I'm no expert diyer so go easy on me if I've suggested a wrong idea

 

[Richard C]

1) Should I remove existing chipboarding completely and then replace with 22mm ply and tile over.

Chipboard of any sort has no real place in a bathroom; or anywhere else for that matter but that’s progress I suppose; my advice is rip it up. You will find it very difficult if not impossible to get to get 22mm WBP ply.

2) Remove existing chipboard floorboard, replace with 18mm WBP ply and then fit hardie 6mm backerboards and then tile over.

Opinions vary on here but I mostly use 18–25mm WBP as a base depending on the floor structure; I asses things like joist size, spacing & span, how flexible it is & go from there but if your in any doubt use 25mm, lay it correctly & seal the back. I tile directly onto the ply; never found it necessary to use backer boards & never had a failure of any sort in nearly 5 years but you will get conflicting advice.

3) Leave good chipboarding and replace water damaged ones with the same new ones. Then fit Hardie 6mm backer board and tile over.

As I said, personally I don’t think chipboard has any place in a bathroom, especially if you’re going to tile it.

4) Then I guess there is all of the above with the addition of a Homelux membrane (or similar product).

Membrane not necessary as well IMO unless it’s a wet room.

While I'm on the subject of Hardie backer board and Homelux membrane: I was planning on using the Homelux matting onto plasterboard for my shower cubicle. Would I be better using Hardie backerboard (instead of plasterboard. One wall currently has no boarding at all and the other with plasterboard will need removing for pipework anyways) and then Homelux membrane over the top for this application as well? Is that overkill?

Only ever use Moisture Resistant plasterboard in a bathroom & never in a wet area unless it’s tanked. Given the choice, I will never use PB in wet areas only tile backer boards & tile straight onto that after sealing the joints. I don’t use a membrane as well as the backer boards, IMO it’s not necessary in a domestic environment unless it’s a wet room; but you will probably get conflicting advice.

Use only quality trade adhesive & grout of the correct type & follow the instructions.

 

[DazJWood]

Great thanks very much for the advice!

It certainly is confusing for the non experienced and as you've said there's lots of conflicting advice on the forums amongst diyers and professionals alike. Tis a bit of a minefield! If it works though, I guess there are no clear wrong or rights ways just ideal ways of doing something.

Thanks,

Daz

 

[Richard C]

Your welcome

 

[DazJWood]

I've bought Excel Bond Rapid Flex Adhesive for the marble floor tiles.

If I were to use Hardie Backer boards on top of 18mm ply would this adhesive be the correct stuff for going onto 6mm Hardie Board? When I bought the tiles I told the guy I was putting them down on at least 18mm plywood and he suggested this adhesive saying anything less than 18mm he'd recommend something different. As the Hardie board is only 6mm thick will this make a difference to using this adhesive?

 

[Richard C]

Sorry can’t advise on the adhesive as I’ve never tried it, I only ever use BAL products.

Regards fixing backer boards over ply; I would only use backer board if over boarding an existing floor that wasn’t up to it & it’s not something I would be entirely happy with.

As I said, a combination of the 2 isn’t something I do or believe is necessary either; a new floor is by far the best way to go & providing you use the right thickness of ply for the joist construction & it’s properly fixed & supported, you don’t need a backer board as well.

 

[DazJWood]

OK thanks again!

Just one more question (last one I hope ), what do you recommend to seal the back?

 

[Richard C]

The purpose of sealing the back of the ply is to keep it dimensionally stable by avoiding the possibility of moisture/water being absorbed into the back; this would cause it to expand, curl upwards & crack the tile adhesive/grout. I should clarify that this is a recommendation by BAL which are the only products I use; they recommend priming the back with BAL Bond SBR but in reality any SBR based (waterproof) sealant will do the job.