Forego base plaster/sealing?

Hello everyone,

I hope this topic fits in this subforum, otherwise feel free to move it.

In the next few weeks, we will be preparing the terrace (gravel bed, on which sand and paving stones will be laid later). The upper edge of the future terrace surface ends almost exactly at the edge of the ground floor insulation to the basement insulation, see the photo below. The top coat/plaster/paint will be applied to the ground floor insulation next week.

Our site manager said that it is completely sufficient to cover the basement insulation with a dimpled membrane and then lay the gravel/sand/pavers "in front of it". Only if it were above the ground level would one have to seal with a base plaster?! Since the base plaster would be billed separately by the general contractor anyway, this is definitely not a "brush-off" from him to save money/effort.

However, I am reading everywhere how important proper sealing of the base is, with sealing slurries/bitumen layers, etc. Is this actually not applicable in such a case?

The site manager explained to us that under the already installed dimpled membrane there is no additional sealing etc., and since everything is later below "ground," the same applies to the rest... If relevant, the basement is made of waterproof concrete (WU-Beton).

Thank you very much for your assessment!!!

So I'll explain it to you:

Normal plaster draws moisture from the ground. For this reason, base plaster is used and applied about 20 cm above the finished floor level [GO]. Since this is not sufficient, for example, the transition must be sealed with bitumen about 30 cm downward. This would be the case for you at the terrace. If you don't do this, you will later have base plaster like in 1000 houses before you, which breaks off unsightly, and eventually you will have to excavate everything and redo it. All just because you saved 100 euros on bitumen coating!

seal the transition with bitumen about 30cm downwards. That would be the case for you at the terrace now.

Thank you very much for the explanation
That means, to be on the safe side, from the edge of the ground floor insulation about 30cm downwards should be coated with bitumen?

Furthermore, the top plaster should not go up to the edge, but the lower 20cm should be applied as base plaster?

I can’t contribute anything professionally, but yesterday my plasterer said I should quickly coat the base currently exposed during the renovation with bitumen as well. Better safe than sorry... some would do it, some wouldn’t, since the old one is still basically on there. For me it was clear that this is now annoying extra work, but if moisture gets through I’ll regret it in bitumen color. I can’t judge whether it’s important or not, but sealing against water can’t be wrong. So I’m just going to do it now.

Thank you very much for the explanation
That means, to be on the safe side, from the edge of the ground floor insulation about 30cm downwards should be coated with bitumen?

Also, the top plaster should not go right up to the edge, but the bottom 20cm should be done as base plaster?

That's exactly how it should be.

Thank you both!

: Which product did you use? I have now found "SAKRET sealing slurry," but for the lower part a bitumen coating should be sufficient, right? Can you use normal bitumen coating there, e.g. something like "black blocker"?