Tiling on anhydrite screed which has been down for over two years

[GaryM]

Hi All,

 

I'm just looking for a bit of advice.

 

The house rebuild has taken longer to finish than planned, so the screed in the hallway has now been down for over two years and used as normal, the house has been water tight for 3 years and ufh in and working for over 2 years

 

The screed is low laitance anhydrite liquid screed with wet UFH under it, around 22 m2

 

To be fair it seems to wearing very well, with no cracks.

 

1. Do I still need to do a full sand of the screed ? 

 

2. I'm using a large 800 x 800 porcelain tile, I was intending to prime it first, and then tile, I wasn't intending to use a  decoupling mat, does this sound ok?

 

Thanks

 

Gary

 

 

 

 

 

 

 

[Mr Punter]

I would have thought that any laitance would have worn off through foot traffic and cleaning and your plan seems OK.

[Bonner]

Separate issues; moisture, adhesion and movement. No doubt it will be dry after 3 years. Any remaining laitance will be fairly obvious and easily removed. A decoupling mat is still recommended to allow thermal expansion without cracking the tiles.

[GaryM]

24 minutes ago, Bonner said:

Separate issues; moisture, adhesion and movement. No doubt it will be dry after 3 years. Any remaining laitance will be fairly obvious and easily removed. A decoupling mat is still recommended to allow thermal expansion without cracking the tiles.

The anhydrite screed is suppose to have low expansion and the manufactures  say no decoupling is needed.

Looking at the screed there are no cracks in it so it seems expansion has not been a problem as yet.

 

As you can tell I really don't want to lay decoupling  , but if the common consensus is it is needed, then I will.

[Bonner]

The screed might not crack but large porcelain tiles will expand at a slightly different rate. I also laid 800mm tiles on Anhydrous screed and wasn’t going to use a mat but decided to in the end. That’s just my experience, @nod is the real expert!

[saveasteading]

3 hours ago, GaryM said:

it seems expansion has not been a problem

Expansion isn't a problem, contraction is, mostly for the first month when the ecreed is changing chemically, and drying. After that, in real life, the screed warms a little and cools a little and really shouldn't move much, and tiles will move with it if you have allowed expansion gaps.

 

[nod]

Flow screeds are usually fine without a mat 80% of the fllow screed that I tile have no matting  Usually tiled within a week of being laid They tend to be commercial so no UFH 

The others tend to be one off builds 

with UFH and are that spooked by YouTube They go for Ditra 

As a tiling business you would be surprised how little say I have on the jobs we do 

 

I’ve just laid the screed on ours Bit had I gone for flo like I originally intended I wouldn’t have used matting