UFH Screed thickness and makeup

[pilgrim]

I think I've probably read too many articles and opinions on the best way to build up my screed layer.

 

I was originally planning on laying a sand and cement, screed layer at 70mm thick. But have seen some fibre self levelling screed products offering thicknesses down to 50mm. As well as other places recommending laying a sand and cement screed then finishing it off with a layer of self levelling compound before laying the laminate flooring.

 

So I was wondering if anyone can offer some clear advise based on what they have done in the real world, not just marketing promises! I want a floor that retains and distributes the heating well, im not too fussed about a fast response time to temperature changes from the Boiler.

I will have over 200mm of insulation under the screed and a laminated wood flooring on top. 

 

Im probably just overthinking it all and over worrying but I want to avoid as many nasty surprises and foolish mistakes as I can!!

 

[JohnMo]

We used 100mm concrete, slow response, which suits us as we like a steady temperature, one heating cycling per day.  We have 200mm PIR below the the UFH pipes.

[Temp]

Think ours is around 65mm with stone on top. Not enough insulation at only 80mm. Works OK but would go for lot more insulation if building again.

 

I would also put expansion gaps where the screed in two rooms meet at a doorway. Eg Don't screed through a doorway. We found out the hardway that it will crack and the crack can be curved in one room more than the other. An expansion gap acts like a deliberate crack but at least its straight and you know where it will be and can tile accordingly. You need one even if only one room is going to be tiled.

[Temp]

The other thing to be careful of is anhydrite screed laitance. This can make if hard to glue tiles or wood floor to. 

 

https://www.bal-adhesives.com/tiling-onto-calcium-sulfate-anhydrite-screeds/

 

Edited March 4, 2022 by Temp

[pilgrim]

9 hours ago, Temp said:

I would also put expansion gaps where the screed in two rooms meet at a doorway. Eg Don't screed through a doorway. We found out the hardway that it will crack and the crack can be curved in one room more than the other. 

 Ohh thanks that is a good tip that I hadnt considered.