ᐅ Bitumen waterproofing membrane on the concrete slab

I also think Kaja is great!

It has to be Katja, says Katja.

I have now taken a look at the waterproofing standard DIN 18533, and it specifies that for positive water pressure—like we have—the waterproofing is applied beneath the slab, not above it.

This suggests that the waterproofing is indeed not done on top.

I find that a bit uncomfortable because I have to fully trust the company and won’t be able to verify later whether everything was done properly. So now I’m wondering if I should still waterproof the top of the slab as well… kind of as an extra safety measure.

Are you building a basement? It is usually constructed as a waterproof concrete shell ("white tank"), so you typically do not need additional waterproofing under the slab.

No, without a basement.

We also used the black tank method, and our sequence from bottom to top was: 1. blinding layer, 2. bitumen waterproofing with torch-on membrane, 3. insulation, 4. concrete slab.

In my opinion, applying it above doesn’t make sense, as water would likely rise through the walls if it comes through the slab.