Calcium sulfate screed vs. conventional cement screed

Hello everyone,

we are considering using a calcium sulfate flowing screed instead of a conventional cement screed. According to our screed layer, the installation thickness is about 20% less, which improves the effectiveness of the underfloor heating. It is also said that heating costs can be saved as a result. I do not yet have a cost calculation.

What do you think? Are there any disadvantages of calcium sulfate flowing screed compared to a conventional cement screed?
Thank you very much!

No, there are no disadvantages. The advantage of flowing screeds simply lies in the fact that the encasement of the heating elements by the screed mortar is better with flowable masses. As a result, the heat transfer from the pipe casing to the screed mortar is also better, more effective. But anyone who tries to count the peas (sorry: the pennies) they could save here with a calculator will hardly find the objective basis for their arithmetic skills (e.g., as a spreadsheet). Calcium sulfate flowing screeds (CAF) can be installed in thinner layers than cement screeds, but their material costs are somewhat higher again. So it all balances out largely! A plus point is the faster response time of CAF compared to conventional installation due to better heat transfer and lower installation thickness. Regards: KlaRa

No, there are no disadvantages. The advantage of flowing screeds lies simply in the fact that the sheathing of the heating elements by the screed mortar is better with flowable masses. As a result, the heat transfer from the pipe sheath to the screed mortar is also better, more effective. But anyone who tries to count the peas (excuse me: the pennies) they could save with a calculator will find it difficult to find an objective basis for their calculations (e.g., as a table). Calcium sulfate flowing screeds (CAF) can be installed in thinner layers than cement screeds, but their material costs are somewhat higher again. So it all largely balances out! A plus point is the faster reaction time of CAF compared to conventional installation, due to better heat transfer and lower installation thickness. Regards: KlaRa

At that time, we were advised against "flowing screed" because it swells with water damage and then must be completely renewed. That means the damaged area plus the additionally damaged section. The cement screed, on the other hand, only has to be replaced at the damaged spot (e.g. in the area of a pipe break), the rest can dry again... Of course, with cement screed, the floor must first be sanded down so that the tiler is satisfied. Is that correct, or did we misunderstand that (8 years ago)? :-)

Of course, with a cement screed the floor must first be ground down so that the tiler is satisfied.

Uh? Why is that?

The tiler insisted because our tiles had a large format for the time (60*60). I have to add that our tiler was 110%. There were indeed tiny bumps in the cement screed. Of course, that is a disadvantage of cement screed. But the tiler finished grinding the entire ground floor in less than half a day (almost 90 sqm).

Äh? Warum das?

Sorry, but this is again one of those pieces of information from the industry where I have to hold myself back!! Half-knowledge only fuels uncertainty. It is correct that floor screeds based on calcium sulfate are completely suitable for both residential and commercial areas. It is also correct that calcium sulfate screeds are sensitive to penetrating moisture and wetness. In residential areas, therefore, floor-level shower trays are always made of cement screeds; if prefabricated shower trays are used, the bathroom surfaces (as well as the wall surfaces) are sealed with an alternative waterproofing. A water damage event is not "normal use," but always, as the name suggests, an event one cannot anticipate. For cement screeds, which are also suitable for wet areas, nothing needs to be "replaced" anyway, why should it? Concrete structures using cement as a binder are even built underwater without it affecting them. Neither cement nor calcium sulfate screeds need to be "ground down." Grinding down always means: defect correction. Cleaning grinding, on the other hand, is mandatory before every floor covering installation and independent of the screed binder! This serves to clean the screed surface from dirt deposits, fine sediments, etc., so that subsequent layers (on the primer) can adhere properly. Yes, quite a lot of flooring technology has indeed been misunderstood (or incorrectly conveyed).
-------------------------
Regards: KlaRa