Best construction/prep method for bathroom floor?

[peterparker]

Hi there

I'm new to the forum so please bare with me. I am having an en suite shower room fully tiled with electrical ufh, it used to be a bedroom. At the moment there are just joists, the boards are shot so will be going in the bin. It's quite a large room ie 3.8m x 2.7m.

What I'd like to know is the best way to construct the floor from the joists up. Cost is not an issue, it has to be a perfect job which lasts.

I've read lots of historic posts and know that I need some combination of 18-25mm wbp ply, hardie backer, insulated board, ditra matting, latex, flexible adhesive etc.

I just need to know the exact order they go in etc.

Thanks in advance for your help

 

[peterparker]

I'd really appreciate some advice on this please.

Thanks in advance.

 

[Chalker]

My 10 penneth.

make sure joists are level and flat.
put felt on any pipes to stop creaking.
glue and screw noggins at 450 or 18 inch centres, depending on ply size.
glue and screw 18mm exterior grade ply.
prime boards.
Fit insulation boards with SPF and screw with washers.
tile using SPF

or fit backer board and tile.

 

[TJ Smiler]

And that's that then :smiley2:

 

[peterparker]

My 10 penneth.

make sure joists are level and flat.
put felt on any pipes to stop creaking.
glue and screw noggins at 450 or 18 inch centres, depending on ply size.
glue and screw 18mm exterior grade ply.
prime boards.
Fit insulation boards with SPF and screw with washers.
tile using SPF

or fit backer board and tile.

Thank you for taking the time to reply, may I ask you a few further questions please?

1) If I use rock wool between the joists is this as good as insulating board? I'd be keen on rock wool as it will provide some sound insulation as well.


2) Some people suggest using 'latex', is this just an additive in the SPF?

3) As belt and braces I might as well use ditra matt, should this go on top of the backer board and then UFH on top of that?

4) Shall I tank the wet areas and if so do I apply the tanking paint directly to the ply?

Thanks again

 

[White Room]

What tiles are you going to fix....

 

[peterparker]

What tiles are you going to fix....

Hi there

80x80 porcelain tiles. These to be exact

http://www.casadolcecasa.com/en/stones-more/#coloriTab#00E1764

Thanks for your help.

 

[Stef]

In question 4 I see you asking about tanking ply?
Is this ply on the floor or is it on the walls?

 

[IHB]

glue and screw 18mm exterior grade ply.

Should ply used onto joists as flooring not be structural ply rather than just exterior grade? Some exterior grade ply isn't very good with voids etc & may not be up to being used a flooring as opposed to just over boarding.

 

[Chalker]

Should ply used onto joists as flooring not be structural ply rather than just exterior grade? Some exterior grade ply isn't very good with voids etc & may not be up to being used a flooring as opposed to just over boarding.

With plenty of noggins its fine. Try deforming a 450x450 piece . Better would be 22mm on a larger floor, but I've never (yet!) had a problem, as long as it is good quality ply. Not from the sheds, there is a massive difference in quality. Best purchased from a good timber merchant.

 

[peterparker]

In question 4 I see you asking about tanking ply?
Is this ply on the floor or is it on the walls?

Hi Stef

I'm talking about tanking ply on the floor, there is no ply on the walls. Two of the walls are external ie brick/block construction, the third will be covered in backer board and the fourth will never see any water.

Thanks

 

[Stef]

Hi Stef

I'm talking about tanking ply on the floor, there is no ply on the walls. Two of the walls are external ie brick/block construction, the third will be covered in backer board and the fourth will never see any water.

Thanks

Personally I would overboard the ply with a backerboard, use an insulation board & tape the joins & it will be waterproof & no need to tank.

 

[peterparker]

Personally I would overboard the ply with a backerboard, use an insulation board & tape the joins & it will be waterproof & no need to tank.

Hi Stef

Are you saying to use ply, backer board, insulation board and then tile?

Thanks

 

[Stef]

No, strengthen your floor from the joists up, fix ply wood then fix a 6mm insulation board.
Or even fit Hardi backer instead of the insulation boards,
Normally I overboard wooden floors with 6mm Hardi glued & screwed.

 

[peterparker]

Thanks Stef.

Any pearls of wisdom in the way the hardi backer should be screwed to the ply? Also which glue would you use.

Cheers

 

[Stef]

It's the way Hardi state it should be fitted.
When we say glue it effectively means mixing up tile adhesive & combing the floor with a 6mm notch trowel then laying the Hardi on top of this.
I mix my adhesive slightly wet as the cement board will sook moisture from the adhesive.
There is a grid pattern on the Hardi & you will see circles indents these are where to fix your screws, I use ScrewFix turbo golds 25mm.
It's pretty straight forward & gives a good solid surface to tile to.
They say standard adhesive to fix Hardi but I use a flexi as it sits better in my head as you are fixing to wood that moves slightly..

 

[peterparker]

Thanks Stef and sorry for the delay in replying.

Because of previous bad experiences and the cost of the tiles I want to belt and braces. So I'd like to tank(using paint) the wet areas and use ditra mat. So two more stupid questions please?

1) Do I tank the ply or the backer board??

2) I take it the ditra should be 'glued' to the backer board using the same flexible adhesive? But which sized trowel should be used?

All the help so far is really appreciated.

 

[Stef]

No need to tank the floor if your using Ditra (its waterproof) just make sure you use waterproof tape in all internal corners.
Tank the walls with a suitable tanking kit, I use Mapei aquadefence but there are a few on the market, Ardex sticks like the proverbial & is one of the best out there.
Ditra is only effective on lateral movement it will not help if there's any bounce in the floor.
Fix with either a 4mm or 6mm notch trowel.

 

[peterparker]

Thanks Stef.
I'll be using backer board on the walls in the wet areas. Do I just apply the tanking paint onto the backer board and then tile straight over it?

Cheers

 

[Stef]

If your using backerboard on the walls then get a waterproof board, something like Wedi, Marmox or Jackoboard if you can get it & then you just need to waterproof the joins & internals, save a lot of hassle.

 

[peterparker]

Hi Stef
The builder has actually already bought the hardie backer board. So shall I just cover it in tanking paint?

Thanks

 

[Stef]

If it's already been bought then yes just tank it out.

 

[peterparker]

Thanks Stef, your advice has been very helpful.