Ditra 25 and Kerdi Keba for floor, walls and wetroom? - Tile Advice

[Chris Churchill]

Hi all, I'm not much of a forum poster, and am also new here to this one.
Additionally, in pre-admission, I'm no professional tiler (although I've successfully performed various vast scale tiling jobs at home), just an avid DIYer.

My situation which lead me to post here revolves around me starting a new first floor extension where I'm installing both a new main bathroom and en-suite which I'd like to wetroom.

As this is on the first floor in a 1930's house, supported by 7x2 joists I am going over timber floorboards. These boards are good and solid, and thankfully, I've got a route to plumb the wetroom trays under the floor without affecting any joists (which is rather fortunate).

Additionally, to accommodate for lateral movement (being on wood and all) I've bought myself 30 meters of Ditra 25 and 60 meters of Kerdi Keba band which I managed to pick up at a really good price.

So, now to my enquiries... :

1) Is it better for me to rip up the floorboards and replace them with 25mm ply before laying the Ditra (keeping in mind that the existing floorboards are perfectly sound)? Additionally, should I be laying anything ontop of that before the Ditra? (This seems like quite a controversial topic)

2) As I have enough Ditra to cover my floor space in spades, can I use this leftover to tank my walls too (NOTE: these [stud] walls don't exist yet, so insert preferred backing board of choice here) or should I:
a) Aquaboard the walls and use paint on tanking?
or
b) Get fabric membrane - like the Kerdi membrane?

2) With regards to how to apply the Kerdi Keba band across all screws and cracks etc, do I have to get the Kerdi Coll adhesive or will a good flexi adhesive do the job? - If so, what do you recommend at a sensible price?

3) As Im using Ditra 25 over the floor, and am installing a wetroom tray, can I use the Ditra over the tray, or will that affect the tray fall? If so, do I have to use a membrane sheet instead?

Naturally, I'd like to use as much as what I have first before I go out an spend more before I get told off for blowing our budget on substrate, but naturally, sealing is cheap and leaks are expensive (figuratively speaking anyway).

Apologies for so many questions. I realize that several have been asked before on this forum, but none quite in this context and could do with some advice before I move forward. I'm also open to hearing about any better solutions to constructing a wetroom, but I'm traditionally on "a budget" so don't really want to pay the moon.

Any on topic and relevant responses welcome!

Many thanks.

 

[Old Mod]

1) Is it better for me to rip up the floorboards and replace them with 25mm ply before laying the Ditra (keeping in mind that the existing floorboards are perfectly sound)? Additionally, should I be laying anything ontop of that before the Ditra? (This seems like quite a controversial topic)

Firstly Hi and welcome to the forum Chris.

It’s not about your floorboards being perfectly sound, it’s about your floor being free of deflection, (bounce) so it’s better to remove floorboards and replace with either 22mm no more ply or GIFA Board, these are both inert and structural boards.
If these boards are used, no further boarding is required.
Timber is not a good substrate, period.
Failing that, overboarding your existing floorboards can be achieved with a 6mm cement board such as Hardibacker, glued and screwed with joints taped.
@HardieBacker

 

[Old Mod]

2) As I have enough Ditra to cover my floor space in spades, can I use this leftover to tank my walls too (NOTE: these [stud] walls don't exist yet, so insert preferred backing board of choice here) or should I:
a) Aquaboard the walls and use paint on tanking?
or
b) Get fabric membrane - like the Kerdi membrane?

2) With regards to how to apply the Kerdi Keba band across all screws and cracks etc, do I have to get the Kerdi Coll adhesive or will a good flexi adhesive do the job? - If so, what do you recommend at a sensible price?

Ditra 25 isn’t traditionally used on walls to tank them.

Why use Aquaboard and paint on tanking when Kerdi Keba board or wedi style are waterproof boards, whereas Aquapanel is not.
Use waterproof boards then tape transitions, board joints and mechanical fixings only.

With regard fixing Kerdi Keba banding to joints and fixings, if you do not use Kerdi Coll to adhere it, you will void all Schluter warranties.

 

[Old Mod]

3) As Im using Ditra 25 over the floor, and am installing a wetroom tray, can I use the Ditra over the tray, or will that affect the tray fall? If so, do I have to use a membrane sheet instead?

There is no need to ditra over the tray, yes the falls would be effected.
Tape only the join between substrate, ditra and tray and around the perimeter.
The tray is both inert and waterproof.

 

[Flintstone]

To add to that, I would be happy using adhesive instead of Kerdi coll in all the none wet areas, and just use the Coll in the wet areas. This all sounds like a good time to add underfloor heating to me? In the wetroom 100% and if budget allows, throughout.

 

[Chris Churchill]

It’s not about your floorboards being perfectly sound, it’s about your floor being free of deflection, (bounce) so it’s better to remove floorboards and replace with either 22mm no more ply or GIFA Board, these are both inert and structural boards.
If these boards are used, no further boarding is required.
Timber is not a good substrate, period.
Failing that, overboarding your existing floorboards can be achieved with a 6mm cement board such as Hardibacker, glued and screwed with joints taped.
@HardieBacker

Understood. Consider the floorboards gone. However, NMP seems to be a bit scarce in my area. Is there a price difference between this vs standard 25mm ply? If so, what are the main property differences between the two - keeping in mind Ditra is wrapping it and an over-looming battleaxe dangling the budget elephant? Should I try hard to get NMP online or keep things simple and rock up to Wickes or local timber merchants for run of the mill ply?

Ditra 25 isn’t traditionally used on walls to tank them.

Again, great and understood it's not the traditional way. However, as I have loads of this spare, could it be used as a (current case) cost effective way of waterproofing the walls? Don't want to spend if I don't have to - especially given the resell value of this stuff (plus the caning I'd get in return). Also, not sure with whats up with my area, but no-one seems to stock Kerdi Keba or Wedi boards so would have to be an online thing with loads of additional faff. Given my general "least line of resistance" philosophy, looking for the most practical solution. Not sure if this bump has any impact on your initial statement?

There is no need to ditra over the tray, yes the falls would be effected.
Tape only the join between substrate, ditra and tray and around the perimeter.
The tray is both inert and waterproof.

Got it. Great. However, a little confused over the YouTube videos where they all seem to use the membrane stuff to cover the trays. Is that just overkill in which case?

To add to that, I would be happy using adhesive instead of Kerdi coll in all the none wet areas, and just use the Coll in the wet areas. This all sounds like a good time to add underfloor heating to me? In the wetroom 100% and if budget allows, throughout.

Yeah, I don't think the entire rooms need packing out in waterproofing. This isn't going to be a set supporting a scene out of "The Shape of Water" after all. So will probably pickup on this bit. However, suggesting underfloor heating is a death sentence for me. We have it in other zones already, but is too much of a kick in the nads to add it upstairs too.

 

[GoneGuy]

I would stick to nmp for the floor as ply today is not the best quality that it used to be years ago.

As with underfloor heating if you message @Uheat - Jake they can get you a price and fitting guide. But it needs to be connected by a qualified electrician

 

[GoneGuy]

Also try @Pro Tiler Tools for kerdi Keba