Screed cracks and UFH

[andrewwest]

Hi all. Have currently got builders in doing extension which has concrete floor with UFH and screed over the top. UFH has been turned on to dry the screed, raising the temp by 2 deg every two days. Some hairline cracks have started to appear in one room, and wondering if this is a problem? Builder is currently on holiday for the long weekend so can't ask, and would be good to get some outside opinions too as don't want to be fobbed off with a quick but wrong solution. Pictures of cracks attached.

Thanks. View attachment 411907

 

[Wayners]

Why would you turn on the heat because heat would crack plaster or concrete?
If you wanted to speed up drying a dehumidifier and fans moving the air..

 

[Mr Chibs]

You shouldn't really be using the floor to dry it out.
It won't really make a difference to the heating, and if you wanted to fill it, just brush in dry and and cement, this will largely be cosmetic. You wouldn't know if the tiles were down.
If you are having tiles, are they putting down a decoupling membrane first?