Screed crack UFH - is there a problem?

[Coopobot]

Hello all.

I was hoping for some help with UFH issue. There seems to be many posts with similar issues but no answer fits all.

I have had builders round to do a lot of work at my house. Part of it was digging out the floor and laying a wet UFH system.

The room is approx 34sqM
Damp proof membrane
Layer of insullation - 100mm i think
A fast drying screed with fibre in it. Not sure on exact depth.

It was laid and drying for approx 2 weeks before the UFH was turned on. It has been pretty warm in the room aswell with the recent warm temperatures here. The builder and person who laid the screed assured me this was plenty of time for it to dry.

Since turning the UFH on, a few cracks have appeared. The builder insists this is normal
But after reading other threads im a little worried. Its only on at 24 degress C.

I was planning on raising it 1 C a day to 30 and then back down.

It does not sound hollow, and is not raised in any way.


Do these cracks need to be filled?
Can i tile over them with flexible adhesive / grout?

Do i need to worry about these cracks or is everything ok with them?

 

[Flintstone]

Cracks are pretty normal, what is the screed?
I would fit dural durabase before tiling.

 

[Coopobot]

I have been informed its a ‘Tarmac Truscreed’ which reduces the drying time as it has a higher cement content than normal screeds.

It is also ‘fibre reinforced’.

 

[White Room]

Decoupling of your choice as already mentioned.

 

[Glynn]

The Tarmac Technical Data Sheet states,

"NOTE: Do not use hot air blowers, underfloor heating, or other means of accelerating drying in the early life of the screed".

This may be why the screed cracked and why this thread is recommending the de-coupling mat.