Expansion of cement screed garage - Is 6cm of cement screed sufficient?

Hello everyone,

I have a small problem.
In our garage, cement screed is to be laid.

The garage is 5m wide and 6m long.
On the floor slab, the highest point should have a 21cm floor buildup and the lowest 18cm (for the slope).

The responsible craftsman said that I should lay 12cm of Styrodur everywhere. Two layers of Styrodur a 6cm each. A perimeter insulation strip at the edge and another layer of construction foil on top of the Styrodur.

My question: is 6cm of cement screed sufficient as a buildup for the weight that will later be on it?
And is the buildup okay like that?

Best regards, Crimson

3cm slope over 6m? That is 0.5%. What is that supposed to achieve?

3cm over 4m is planned, the rearmost part should run straight as it is also intended as storage space. 0.75% is not quite one percent, but unfortunately it was not possible otherwise

1% brings nothing at all.

I shouldn't have started with the slope at all ;)

I'm more concerned about the thickness of the cement screed

Best regards

Hello questioner.
First of all: the question about the slope also seems quite justified to me at <1%, as it is so low that not only the function is questionable but also one could work with a significantly thinner composite screed (35mm).
However, if for reasons which I cannot and do not want to assess here, an insulation layer is to be installed under the screed, then with an assumed surface load of 4kN/m² a screed
CT-C35-F5-S65
would result.
This means: compressive strength 35N/mm² and flexural tensile strength F5, all of it 65mm thick as a "floating screed" on (compressive resistant) insulation layer.
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Good luck!