Is Dimtra matting needed on screed flooring?

[Hotknife]

We have 60m of new concrete screed, with wet underfloor heating installed. The screed has totally set a few months ago but does have a few hairline cracks in the surface from setting.
We are looking to install a limestone floor of about 20mm over the entire 60m.
My query is, will flexible grout be sufficient to stop the cracks transferring to the tiles or should we look at the ditra matting system as well ?

Would people advise matting for the screed flooring or can we get away without it?

 

[tpt]

No its not necessary, but its a good way of separating the movement of the layers. The concrete and the tiles will expand\contract at different rates, plus the screed will settle over time. The cracks your seeing are most likely that settlement. Often ditra will be specified for large unbroken runs, or screeds that are still in the drying phase.

If you have a large unbroken span then expansion joints can be used.

P.s. with a light limestone you should use a white adhesive to stop shadowing through the tiles.

 

[Hotknife]

Thanks for the swift response. The largest distance is about 11m by 3m, is what you'd call large.

Are the cracks likely to transfer to the tiles without the matting and do you think that flexible adhesive is enough to absorb the movement between the screed and tiles.

I'm not so keen on expansion joints as from what I've read they are visible above the tiles once they are laid. Is this the case?

 

[tpt]

hi there, yes expansion joints are visible. 11m2 is long enough need them.

An s1 flexible adhesive will absorb the movement introduced by your heating but not any settlement. typically this will stop after a period of time but obviously its hard to say when its finished moving!

 

[Hotknife]

Ok, gonna jump and order the tiles. Thanks for the help and info.