Should a terrace concrete slab still be sealed despite having a drainage mat?

Good day to the forum

I intend to lay concrete slabs or ceramic tiles on my terrace concrete slab using pedestals.
For this reason, I have researched several suggestions online. It is recommended to apply the sealing slurry twice on the slab and finally lay a drainage mat on it (and then place the pedestals on top).
Can you confirm this? Would a single application of sealing slurry not be sufficient? Or instead of the sealing slurry, a single coat of bitumen? Emissions/odors from the bitumen coat?

Thanks and regards

Dirk

I wouldn’t do anything; any coating on the substructure prevents water from seeping through.

I would place the pedestal supports on rubber buffers for acoustic decoupling and that’s it.

What now? The water is not supposed to run along the concrete. No sealing slurry, just drainage mat?

Regards

Dirk

Hello Dirk. If the floor slab was installed in contact with the ground, so there are no rooms underneath, waterproofing is not required. Nor is drainage. If the floor slab does not have a slope, which I assume, it is completely irrelevant with the construction method described above. Well-compacted concrete hardly absorbs water (we differentiate between water and moisture!!). Without a slope, puddles would always remain on the concrete surface, with or without waterproofing & co., just as they do now. You can apply a sealing slurry, but it has neither a positive nor a negative effect. You want to lay concrete stone slabs or ceramic slabs on pedestals? Please keep in mind that such slabs are only load-bearing without rear support from a thickness of 40mm (and we do not have that with raised slabs). -------------- Good luck: KlaRa

Hello Dirk.

Please remember that such panels are only load-bearing without rear support from a thickness of 40mm (and we do not have that in propped panels).
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Good luck: KlaRa

Hello KlaRa

I did not understand your last sentence. For panels with thicknesses of 20mm or 30mm and dimensions of 400mm x 400mm or larger, I would have placed a prop or similar support centrally from below in the middle of the panel. That should be sufficient so that nothing breaks in.....

Best regards

Dirk

For the mentioned dimensions, no support needs to be placed in the center for a total thickness of ≥40mm! It is also common to have supports where a corner area (of three other adjacent laid panels) is used. For 20mm thick panels, the load-bearing capacity is limited. Corresponding references can be found in DIN 18560 Part 2. Assuming a surface load of up to 2kN/m², the aforementioned panel thickness is required for individual/point loads up to 100kg. This corresponds to a static surface load of up to max. 200 kg/m². If dancing were to take place on the surface, the situation would already be less favorable. For the requirements in residential construction, an individual load of up to 2kN with a surface load of up to 300 kg/m² is assumed. However, in this case, the 40mm panel thickness is no longer sufficient and must be increased to at least 55mm thickness. Another installation or laying variant (with thinner panel thicknesses) would of course be to place the upper layer above a drainage panel in a gravel fill. Die (written in capital letters and bold) laying variant does not exist. The accompanying conditions of the object and the planned type of use determine which variant or construction method must be applied.
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Regards: KlaRa