Flagstone Floor Screed Depth

[Jimmyriddle]

Hi,
I am in the process of building a house and I am planning on using a thick flagstone (Supplier recommends allowing for a 35-40mm laying thickness) on my kitchen diner floor, I am using a sand and cement screed that building regs state should be 65mm thick with UFH. I want the house to flow flush between floor levels... can I reduce the screed thickness to accomondate the thick stone so that it will be level with the carpets or do I need to increase screed depth where the carpets are to accomondate the flagstone.
Thank you in advance

Regards
James

 

[Dave]

Hi,
I am in the process of building a house and I am planning on using a thick flagstone (Supplier recommends allowing for a 35-40mm laying thickness) on my kitchen diner floor, I am using a sand and cement screed that building regs state should be 65mm thick with UFH. I want the house to flow flush between floor levels... can I reduce the screed thickness to accomondate the thick stone so that it will be level with the carpets or do I need to increase screed depth where the carpets are to accomondate the flagstone.
Thank you in advance

Regards
James

Hi James. Use a pourable screed. They go in much thinner.

 

[Jimmyriddle]

Hi James. Use a pourable screed. They go in much thinner.

Will It compromise floor strength if I do it a bit thinner? I dont want the floor cracking or anything daft...I will be using an anti crack mat inbetween the flagstones and the screed.

 

[Dave]

Will It compromise floor strength if I do it a bit thinner? I dont want the floor cracking or anything daft...I will be using an anti crack mat inbetween the flagstones and the screed.

Pourable screeds are very strong. Usually screed depth is around 35mm.

 

[Ajax123]

As Dave Says you could use a liquid screed but with UFH you will still need to allow for about 20mm cover to the pipes so a minimum 36mm at the very thinnest point. That's if you use a specialist mix design like HTC from our range (others are available) Typically with underfloor heating you would allow a 50mm screed with UFH. Only issue is you would not generally be able to lay this yourself so if you are set on doing the screed yourself you need to look at proprietary screeds. Building Regs don't state an absolute depth and actually don't have the power to specify materials and depths. You simply have to show compliance and in the case of proprietary products that means manufacturers specification or instructions. Another alternative if you want to do the screed yourself would be to go for a modified sand cement like a SBR screed. All cement based screeds can be prone to cracking especially with UFH so where natural stone is being laid on top you should use a decoupling membrane to mitigate the risk of the cracks reflecting through the tiles.

Bear in mind also the requirements for Bay size and movement joints which cannot really be avoided if you want to do it properly. These can make it difficult to have a tiled installation flow through a whole floor from one room to another.