ᐅ Finishing Cement Screed in Garage – Is 6 cm Thickness Enough?

Hello everyone,

I have a small problem.
We plan to install a cement screed in our garage.

The garage is 5m (16 feet) wide and 6m (20 feet) long.
On top of the concrete slab, the floor buildup will be 21cm (8.3 inches) at the highest point and 18cm (7.1 inches) at the lowest point (to accommodate the slope).

The contractor responsible suggested installing 12cm (4.7 inches) of Styrodur insulation everywhere, in two layers of 6cm (2.4 inches) each. A perimeter insulation strip should be placed along the edges, and a layer of construction foil laid on top of the Styrodur.

My question is: Is a 6cm (2.4 inches) cement screed sufficient to support the weight that will be on it later?
And is this buildup acceptable as planned?

Best regards, Crimson

3cm (1.2 inches) slope over 6m (20 feet)? That’s 0.5%. What is that supposed to achieve?

3cm (1.2 inches) over 4m (13 feet) is planned, the rear section should be straight as it is also intended to be used as storage space.
0.75% is slightly less than one percent, but unfortunately, there was no other way.

1% doesn’t make any difference.

I probably 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 seems quite justified to me as well when it is less than 1%, since it is so minimal that not only the functionality is questionable, but you could also work with a significantly thinner bonded screed (35mm (1.4 inches)).
However, if for reasons that I cannot and do not want to assess here an insulation layer is still to be installed beneath the screed, then with an assumed distributed load of 4kN/m² (85 lb/ft²) a screed CT-C35-F5-S65 would result.
This means: compressive strength 35N/mm² (5,075 psi) and flexural tensile strength F5, all at a thickness of 65mm (2.6 inches) as a “floating screed” on a (compressive-resistant) insulation layer.
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Good luck!