Tiling onto Ply, can it be a success?

[AD1]

Hi,

I've been doing alot of research prior to tiling the ground floor of my home, approx 40m2. The structural floor is 18mm Ply and after reading all the horror stories of failed floors I am getting nervous on whether I am looking at failure before I start! I can't find anywhere online a successful tile on ply job, So ... Can it be done?

The floor construction is 4x2 joists, spaced at 400mm centres, levelled and fixed. I have already installed underloor heating, 70mm celotex between joists and 30mm anhydrite screed level with the top of the joists. Then overboarded with 18mm Ply. Ply has been sealed on the underside and edges with SBR and glued and screwed every 150mm with joints finishing on the joists. The biggest room span is 3m and is supported halfway by a small supporting wall, So joists only span 1.5m.

The floor is flat (no more than 3mm over 2m) and very solid. There is no deflection in the floor except 1 board edge about 2ft will move down 2mm if pressed hard (Screed must not of been perfectly level and so left a 2mm void between the screed and ply), I plan to fix this but unsure how? The rest of the floor is very stable with no movement.

I have bought Ditra and Ardex Af200 to bond to ply (3mm V notch trowel) .. then tile 600 x 600 rectified porcelain tile with Ultimate S2 adhesive, 20mm x 10mm round notch trowel, 3mm grout line, Lash levelling clips, and grout with BAL Superflex wide joint with GT1 Admix.

The underfloor heating has been in 1 year already, screed was left 1 month before ply, commissioned correctly and is the heating is working perfectly. I plan to turn it off 48 hours before starting anything.

So my question is, is there anything else I could possibly do to prevent failure? After reading online I'm almost at the point of putting down engineered oak onstead of tiles.

Has anyone successfully tiled on Ply with ufh that has lasted?

Thanks, Adam.

 

[Old Mod]

Hi and welcome to the forum Adam.

Yes, return the Ultimate adhesive, it’s an S2 class and not suitable for use on Ditra according to Schluter, your guarantees would be void.
Obtain an S1 class instead, this is approved.
If the store sells ultimate, my guess is they sell Sataflex, exchange it for that, don’t forget your refund, it should be considerable.
Get white or grey adhesive whichever is closest to your grout colour.
It sounds like you’ve researched fairly well.

 

[Old Mod]

Has anyone successfully tiled on Ply with ufh that has lasted?

Thanks, Adam.

I would be as brave to say all of us.

 

[Old Mod]

Setaflex standard set, not rapid, you’ll throw more away.

 

[Waluigi]

What span is the 4” x 2”?

 

[Old Mod]

It says 1.5m span, which is within the parameters of C16 97 x 47mm joists.

 

[Waluigi]

Oh yeah

 

[Dumbo]

Personally with ditra and dural I find a 4mm notch better . I only tend to use 3mm with anti crack mats such as tilemaster or bal rapid mat .

 

[AD1]

The joists are 4" x 2" and largest span is 3m but halfway is a supporting wall under the floor. They joists only actually span 1.5m unsupported.

 

[Flintstone]

6mm for me with those mats for full coverage.

Am I reading this right, you have put ply over an anhydrite screed with ufh?

 

[Boggs]

I have seen this twice before, there was a poly layer between joists and ply for moisture.
But maybe that was one because the finished floor was timber, can’t remember but worth checking.

Why not stick and screw 6mm Hardie backer to the floor before tiling instead of the Ditra.

 

[Flintstone]

Then turn the heating on in August just in time for it to be warmed up for around bonfire night !

 

[J Sid]

my main concern is is the floor under the ply completely dry!
this is what will happen if you trap moisture under Ditra onto ply.

 

[J Sid]

and that was just a hole in the sealed bag of clay infill for round the ufh pipes.

 

[AD1]

I have read a lot of conflicting opinions on using S2 over Ditra. I decided to go with Ultimate S2 as I read US and UK specs are different and S2 is suitable according to UK spec.

I did think the screed was anhydrite but from a quick Google search it seems it's not. It is a dry mix with fibre glass reinforcement and was shovelled in and packed in between joists and compressed.

The heating works perfectly, UFH manifold flow temp set at 50 degrees, the house is warm and our living has laminate which is warm to touch. Takes around 1 hour to heat up to temperature.

I also chose a 3mm V notch as this is what is specified by Ardex, should I go larger notch? I may need another tub if so.

Thanks for the replies.