Decoupler mat

[Pete]

We have a passive slab and are busy choosing tiles, approx 270 sq m and we would like them to be 120cm x 120cm and a couple of tile shops have said we will need an anti crack mat which I assume is a decoupling membrane. Our slab is generally 100mm thick apart from the load bearing areas and has steel reinforcement within the concrete. What I am asking is the mat a necessary item or a just an in case item in that if the concrete does crack then the tile will not crack?

Not sure if this needs another thread but what have people done with expansion joints? I really do not like them and a tile supplier I spoke to last year said we would not need them but I see them all the time in large tiled areas in commercial buildings and it is another one of those do I or do I not fit them.  TIA 

[Ian]

@Pete

I used a decoupling mat (Ditra 25) on my own build which was approx 70 sq.m of tiles. The 100mm concrete slab was reinforced with a light guage mesh and our UFH pipes tied to the mesh. 

Why take a risk with that much tiling.

 

The main purpose of the mat is so that any cracking in your slab won't go straight up through the tiles. At 270 sq.m it's likely you will need movement joints in your tiles - can you locate them in doorway positions where they will be less obvious?

Edited July 16, 2018 by Ian

[nod]

I’ve been tiling for over thirty years

A lot has changed

Ive just spent 1000 including vat on 150 mtrs of ditra for ours

Due to the UFH 

Though some people decide against the extra expense and have no problems

 

We normally put expansion joints every ten mtrs Like I hate them on domestic properties 

Using ditra help with this But you should put an expansion joint in each door opening 

 

[lizzie]

I have the passive slab same as others. I have 180sqm of porcelain tiles on it. Used the matting, they said we didnt need expansion joints as well.......hope thats right its too late once its down.

 

 

[newhome]

I have a decoupling mat and ironically it’s the actual mat that has delaminated, the 2 layers having come apart. So the bottom is stuck fast to the screed and the top layer is stuck fast to the tiles. None of the tiles or grout have cracked but it makes an odd noise when walked on which isn’t great. 

 

Mine was Dural CI matting. 

[gc100]

Just picking this thread up. My builders have not allowed for a decoupling mat. Now my issue is I have some very large slider windows which have a level threshold with the tile floor and you actually tile in-between the runner for the sliders. Now they have only left 15mm between the anhydrite flow screed and this level. Given the tiles are 10mm, I'm struggling to see how I can fit a matt without the tiles sitting high relative to this threshold? The whole point was to have a seamless level out into the garden with matching tiles. The screed is one large slab pretty much aside from one side of the hallway which above structurally holds the roof up.

 

It seems from what I understand you need 4-5mm adhesive , then the matt, then another 4-5 adhesive effectively doubling the thickness? 

 

Is there anything I can do, aside paying the window company to company back and take all the windows out and enlarge my openings?... 

 

Tiling wise I have a room which is about 6mx7m which has the sliders, leading to a hall that is 24mx 1m, then a couple of bathrooms and util all on the same single floor (only have one!)

 

 

Edited September 22, 2020 by gc100

[CC45]

the adhesive below the slip layer is ~ 1 or 2mm at most.  I spread our out with a 3mm trowell - so ~ 1.5mm deep max.  The issue is the depth of the decoupling matt itself not the adhesive.  I think 15mm is too tight, you need a decoupling layer of 2 or 3mm in total.  maybe @Nickfromwales knows of a solution?

[gc100]

6 minutes ago, CC45 said:

the adhesive below the slip layer is ~ 1 or 2mm at most.  I spread our out with a 3mm trowell - so ~ 1.5mm deep max.  The issue is the depth of the decoupling matt itself not the adhesive.  I think 15mm is too tight, you need a decoupling layer of 2 or 3mm in total.  maybe @Nickfromwales knows of a solution?

 

One of the mats I was looking at said 0.7mm  so maybe doable??  https://www.protilertools.co.uk/product/kerakoll-biotex-reinforced-anti-cracking-membrane--was-idrobuild--50m-roll

 

I could ramp it up as I move away from the windows but would be difficult to pull off perhaps

 

Edited September 22, 2020 by gc100

[Nickfromwales]

28 minutes ago, gc100 said:

 

One of the mats I was looking at said 0.7mm  so maybe doable??  https://www.protilertools.co.uk/product/kerakoll-biotex-reinforced-anti-cracking-membrane--was-idrobuild--50m-roll

 

I could ramp it up as I move away from the windows but would be difficult to pull off perhaps

 

That membrane is as thin as you're going to get, with Ditra etc deeper again, as they are castellated both topside and underneath. With a wet mix of  rapid-set flexi under that membrane you could just keep going over it with a 4"roller as it goes off and keep it as shy as possible. You'd have to mix up for one 1m strip x Xm long at a time and wait until the first sets before going onto the next. Only necessary, as said, where it's uber-critical, so you can relax a little as you move inward away from the doors etc. Depends on the tile size of course.

[Pete]

I know somebody on here had the decoupling membrane de-laminate so be careful of quality, I cannot remember what make it was though