Floor construction - Ply, hardi or Wedi

[roswell]

Hi All,

I am looking to tile my bathroom floor and have been looking at a couple of options for a sound base before tiling:

1 - 18mm ply screwed to the joists;
2 - Hardibacker screwed tot he joists (thickness?)
3 - Wedi board

We are looking to install underfloor heating as well.

Which is the best option (or pros and cons for each). At the moment our builder has suggested the 18mm ply but i think the other two may be better options?

Also, would we need to include an uncoupling membrane?

Thanks

R

[Rich]

Plywood floors...

Have a quick read through the above post. What is no the floor at the moment? I would want min 18mm boil and water proof ply screwed down about 200mm centers. Seal the underside and the edges and leave a 2mm joint in between the boards for expansion (the boards should be staggered). Then on top of this lay a 6mm cement board to give you a good surface to tile onto. Also this will mean that you can use a 200w mat rather than a 150w one directly on to ply. A decoupling membrane is a very good idea if budget will allow.
What tiles are you using? Are you doing the work or a tiler?

[suave]

welcome!

[Rich]

welcome!

Oh yeah, sorry, missed that.

Welcome the the forum

[roswell]

Thanks for the responses.

The article about the ply is very useful and confirmed my thoughts.

The current floor structure is timber joists with T&G floor boards. I am looking to use a ceramic/ porcelain tile (still to be chosen).

I was assuming that the floor boards would be removed before laying ply/ another surface. I was wondering whether you could use hardibacker straight onto the joists and fix at the appropriate intervals, lay underfloor heating, slc, then tile? Or do you need the ply (or similar) then hardibacker? I have only just come across the Webi boards today and thought they looked interesting as an alternative to either ply or hardibacker (just very expensive!). Anyone have any thoughts on Webi?

Do I also need some form of insulation for the ufh if I use ply or hardi? I am insulating between the joists whilst the floor is up.

I am getting this work done by a builder as I have a new baby and don't seem to have much time to do anything else! Though I have done some tiling myself in the past as well aws a new bathroom and kitchen amongst other diy jobs and can become quite pedantic over how things should be done!


Look forward to receiving your responses.

Kind regards

R

[Rich]

My first piece of advice would be to get a tiler to do the tiling. I have never come across a builder that has the first clue about tiling but every builder in the world thinks he does and it ends in tears to often. Builders are not tilers.

I haven't use the Wedi boards myself so I will let somebody who has advise on them. You will still need the ply before you over board, this will give you a solid base and then the cement boards give you a really good surface to tile onto, these are glued down and then mechanically fixed into the floor. This should give you a really good floor ready for tiling and I shouldn't think you will need any other insulation.

[whitebeam]

Hi and welcome..

[peteablard]

Welcome! I agree with Rich, get a proffesional tiler in. Definatley money well spent......

[roswell]

Just to nip this in the bud. The builder is getting individual trades in to do the bathroom - chippies to sort out removal walls and install of new stud wall and door and laying floors etc, electricians to do the lights, underfloor heating etc, plumbers for the erm plumbing and a tiler to do the tiling.

Lets get back to the floor construction ...

[MissTiler]

Some UFH companies also sell suitable insulation boards to cover the ply with, so its worth checking with the company youre getting the UFH from and you can get the lot in one order. Some of foam/polystyrene type boards just need to be stuck down on the ply with tile adhesive.
The British Standard for ply is a minimum thickness of 15mm, it used to be 18mm.

cheers
missyT

[roswell]

Thank you for all the responses.

To summarise, the best option is to:

Use 18mm WBP ply (with underside and edges sealed - with what?) screwed down at 200mm centers. 2mm expansion joints between the staggered boards.
Then on top of the ply lay a 6mm cement board
Then complete with the UHF (200w mat), slc then adhesive and tiles.

Where would the decoupling membrane be installed?

Has nobody used or have any views on Wedi? Anyone?

Thank you
R

[grumpygrouter]

Thank you for all the responses.

To summarise, the best option is to:

Use 18mm WBP ply (with underside and edges sealed - with what?) screwed down at 200mm centers. 2mm expansion joints between the staggered boards.
Then on top of the ply lay a 6mm cement board
Then complete with the UHF (200w mat), slc then adhesive and tiles.

Where would the decoupling membrane be installed?

Has nobody used or have any views on Wedi? Anyone?

Thank you
R

I once saw an advertisement for one type of construction board showing a BMW X5 sat on a 50mm board supported at each end...can't remember which board though!! As to your question, I believe these types of board are designed as an insulating/backing layer prior to tiling and should be fixed to a full supporting surface to ensure stability. Never seen any manufacturers data sheets saying they can be laid straight onto joists!