Working out levels.. Anhydrite screed, mat, adhesive, porcelain tile - TilersForums.com

[hux001]

Need some help please with calculating levels and the build up of the floor to support tiling.

Not sure about the need for the uncoupling mat?
Not sure about the thickness of the tile adhesive?

As I have sliding glass doors to be spec'ed and installed before the screed, I need to gauge the finished floor levels.

My current thinking is that the floor will be built up as shown below.. Happy to be educated!!

1) 50m2 kitchen/living space (10x5) with concrete slab
2) 1000gu DPM
3) 75mm Kooltherm insulation board
4) Slip membrane
5) 16mm wet unflooring heating system
6) 50mm Anhydrite screed (including the UFH)
-Removing laitance and keying surface
7) Prime screed - what product to use?
8) Uncoupling mat - Is this necessary for porcelain tiles?
-Bond mat to screed - what product to use?
9) Tile adhesive - what product and how thick?
10 Porcelain tile - Say 10mm thick, about 1m2 - still haven't selected product


Big thanks for all the big brains who provide their knowledge and experience on this forum.
Also, if you work in the Hertfordshire area and happy to talk about tiling this space, break cover and message me please.

Thanks
Just

 

[Huddersfield Tiling]

Don't attempt to tile it. Unsuitable.

 

[hux001]

Don't attempt to tile it. Unsuitable.

What do you mean. Don't adhere the tiles direct to the screed, decouple with a mat?

 

[Ajax123]

Your spec looks generally fine. In terms of sanding or mechanical abrasion you need to basically remove anything loose and friable and make the screed surface absorbent so the primer can soak in and thus hang on. Typically this needs only to be microns assuming the screed has no defects. The use of an uncoupling mat isnt absolutely necessary but wont do any harm. In terms of primers it does depend on a few things and with adhesives you are best using gypsum based rather than cement based to avoid issues with chemical incompatibility with the screed. That said as long as the screed is dry cement can work fine. Ivexseen a lot of success with kerakoll tile adhesives like Biogel no limits and similar. Alternatively ive seen people use vynil adhesive for sticking down the uncoupling mat. A third alternative is BAL flexbone loose lay uncoupling mat which eliminates all prep as you dont stick it down. A bit more expensive but a lot less work. Feel free to give me a call if you want to talk it through. 07966651006
Alan

 

[Dave]

Don't attempt to tile it. Unsuitable.

Explain why.. that’s twice now you have put members off tiling to anhydrite screeds and given no viable reason other than it’s unsuitable..

 

[Ajax123]

Explain why.. that’s twice now you have put members off tiling to anhydrite screeds and given no viable reason other than it’s unsuitable..

I assume he’s either had an issue which he never understood or resolved or he is badly misinformed. To give you some idea of how suitable anhydrite is for tiling (not that you need it but it benefits others perhaps) we did a survey a couple of years ago and we reckon around 1million or so square meters of our anhydrite screed was tiled. Anhydrite continues to grow partly due to ease of use and partly due to huge benefits it can offer especially with underfloor heating.

 

[Dave]

I assume he’s either had an issue which he never understood or resolved or he is badly misinformed. To give you some idea of how suitable anhydrite is for tiling (not that you need it but it benefits others perhaps) we did a survey a couple of years ago and we reckon around 1million or so square meters of our anhydrite screed was tiled. Anhydrite continues to grow partly due to ease of use and partly due to huge benefits it can offer especially with underfloor heating.

I love them , nice and flat lol…

as for the member above , more than likely full of pop when posting and forgets what he types 😂😂

 

[Ajax123]

I love them , nice and flat lol…

as for the member above , more than likely full of pop when posting and forgets what he types 😂😂

You may be right. All members, including said member if he wants, are more than welcome to call me to discuss how to deal with anhydrite especially if they have difficult sites, bad experiences or simply don’t know enough about it. As you know Dave, without wishing to be immodest, I know a fair bit about it 🤣🤣

 

[Dave]

You may be right. All members, including said member if he wants, are more than welcome to call me to discuss how to deal with anhydrite especially if they have difficult sites, bad experiences or simply don’t know enough about it. As you know Dave, without wishing to be immodest, I know a fair bit about it 🤣🤣

I do yes 😁 and thank for taking time to help members out Alan.. i would rather someone ask than just go ahead and guess what to do.

 

[hux001]

Your spec looks generally fine. In terms of sanding or mechanical abrasion you need to basically remove anything loose and friable and make the screed surface absorbent so the primer can soak in and thus hang on. Typically this needs only to be microns assuming the screed has no defects. The use of an uncoupling mat isnt absolutely necessary but wont do any harm. In terms of primers it does depend on a few things and with adhesives you are best using gypsum based rather than cement based to avoid issues with chemical incompatibility with the screed. That said as long as the screed is dry cement can work fine. Ivexseen a lot of success with kerakoll tile adhesives like Biogel no limits and similar. Alternatively ive seen people use vynil adhesive for sticking down the uncoupling mat. A third alternative is BAL flexbone loose lay uncoupling mat which eliminates all prep as you dont stick it down. A bit more expensive but a lot less work. Feel free to give me a call if you want to talk it through. 07966651006
Alan

Thanks Alan

So if I go for a uncoupling mat such as Ditra25, I understand this would be 3mm thick.
How thick would the adhesive be between the mat and the screed? And the mat and the tile?

Just trying to work out total cross section height to finished floor level.

Just

 

[Ajax123]

Thanks Alan

So if I go for a uncoupling mat such as Ditra25, I understand this would be 3mm thick.
How thick would the adhesive be between the mat and the screed? And the mat and the tile?

Just trying to work out total cross section height to finished floor level.

Just

If you use a 10mm notch trowel the adhesive will press down to about 3 or 4mm as it fills the dimples in the matting. Not sure if the minimum depth is less but the tech department of the selected adhesive manufacturers will be able to confirm

 

[Dave]

Thanks Alan

So if I go for a uncoupling mat such as Ditra25, I understand this would be 3mm thick.
How thick would the adhesive be between the mat and the screed? And the mat and the tile?

Just trying to work out total cross section height to finished floor level.

Just

Very thin as you want full contact. So quite negligible tbh.

 

[TimmoF]

A third alternative is BAL flexbone loose lay uncoupling mat which eliminates all prep as you dont stick it down. A bit more expensive but a lot less work.

I've always wondered about using Flexbone with UFH.
As it's not adhered to the substrate the thermal conductivity must be lower?

 

[Ajax123]

No rule that says things have to be stuck down to heated screeds. Every time you add a layer you redcue the efficiency so eliminating a layer of adhesive would counteract the fact the membrane is not stuck down. I doubt you would notice the difference TBH.