DITRA Mat, Devimat, Tile, plus self levelling?

[mwjburton]

Hi,

We're about to lay the flooring in our two new bathrooms and I need some advice on the order of things.

We have a new ply floor covering which is 99% flat (a few very small discrepancies ; seems to be no more than 4mm overall).

With that in mind, I'm undecided whether I need to self level before tiling. The advice I've received so far is that unless it reaches approx. 8mm, then I'll be ok to lose this discrepancy in the tile adhesive.

So, does this sound alright?

- PVA the Ply
- Lay DITRA Mat onto the Ply.
- Lay Devimat onto the DITRA Mat.
- Tile Adhesive
- Tiles (600x600 Compac Quartz)

If I do need to self level the floor before tiling, at what point in the above list would I do that? What products would you recommend for this?

Many thanks
Mark

 

[Karis]

I assume this is a suspended timber floor? What sort of ply has been used? It must be WBP, standard ply isn’t suitable & the edges & underside should be acrylic primed before laying. What thickness is the ply & what is your joist size/pitch/span.

You have very large tiles which means your floor should be as flat as possible. 4mm isn’t much but it rather depends over what distance. Why are you installing Ditra underneath the UFH? An uncoupling membrane goes over the heater mat & under the tiles! You would be better using a 6mm thermal tile backer board under the matt to reduce the warm up/response time of the UFH. It’s advisable to lay an SLC directly over the heater mat, it will level up the tile base & protect the mat during tiling but, more importantly, will at least give the possibility of repairing the mat in the event of a problem; go straight over the matt with tile adhesive & you’ll never get to it again.

IMO electric UFL is vastly over rated as a secondary heat source anyway. I know it’s very fashionable but unless you have a predictable living pattern, the response time of between 30-60 mins will make it impracticable & if you leave it running as the primary source, it will cost you a fortune to run. I have a UFH system as a primary heat sourse in my conservatory, it works well but can be expensive to run. Installing one as a secondary heating system in a bathroom IMO is questionable &, personally, I'd spend my cash on something more worthwhile. I also assume you’re aware that any electrical work in a bath/shower room must be undertaken, tested & certified by a Part P electrician!

Never ever use standard PVA as a primer anywhere when tiling, it isn't suitable as it remains water soluble & can be a disaster if used in a wet area. Only use an SBR/acrylic primers & then only where recommended by the adhesive manufacturer. You will need a Single Part Flexible (SPF) powder adhesive & use a good quality one, cheap DIY products are mostly inferior.

Check with the supplier of your quartz tiles, depending on exactly what they are, they may need sealing before laying, again before grouting to prevent staining. The will probably require re-sealing on a regular basis as well. Use the correct colour adhesive for your tiles, again to prevent possibility of staining & don’t use white/light coloured grout on floors, it will look rather shabby in a very short space of time.

 

[tictic]

Couple off things ere....

The ditra matting goes under the elect ufh....not ontop!!....then slc again latex based....

The tiles....you will need a Latex Based adhesive.....or a PTB adhesive(this adhesive doesn't use as much water when mixing)....But IMO go with a latex based addy usuing a flexiable fast setting one...


What colour are the tiles....if light coloured use a white adhesive...or dark tiles then grey adhesive...

What thickness is the wbp ply has the edges/underside been primed...

 

[Karis]

Couple off things ere....
The ditra matting goes under the elect ufh....not ontop!!... ...

On a concrete floor &/or with a wet system no question but if you want to provide uncoupling over a suspended timber floor? Ditra say it can be used under or over, depending!

The tiles....you will need a Latex Based adhesive.....or a PTB adhesive(this adhesive doesn't use as much water when mixing)....But IMO go with a latex based addy usuing a flexiable fast setting one...

To be totally safe I wouldn’t disagree but is it really necessary with a latex SLC if the floor is good?

 

[tictic]

With those tiles.....

And you use a normal water based adhesive....you will have major problems...



These type off tiles require a latex based adhesive for a good number off reasons...


The slc latex is just for the elec ufh covering


Wooden floor/elect ufh /and quartz stone tiles!!!!!!......


Do it right the first type...

 

[Karis]

I frequently get criticised for being “belt & braces” but it’s comforting to know there are still others equally if not more cautious; given the tiles & UFH, probably rightly so.

 

[mwjburton]

Guys, thanks so much for the detailed advice, its hugely appreciated and has been fully taken on board.