ᐅ Waterproof concrete slab with moisture barrier

Hello everyone,

I would like to know your opinion on whether it is necessary to install welded waterproofing membranes as an additional moisture barrier when using a waterproof concrete slab (WU slab).

Best regards

This topic sparked a really heated debate here. For me, it still doesn’t make sense how water could "rise up" the wooden walls through 50cm (20 inches) of gravel, 14cm (5.5 inches) of insulation, and 30cm (12 inches) of waterproof concrete. But all the construction professionals involved insisted on this, arguing that the water contained in the building permit / planning permission (BP) could otherwise penetrate through the floor structure into the walls or other elements and cause damage (or something similar). I didn’t want to be the only one arguing about it for days over €1500 (as sometimes, as mentioned elsewhere by another person, one loses the healthy sense of proportion regarding money).
In short: Yes.

superzapp schrieb:

This topic was really hotly debated among us. It still doesn’t make sense to me how water could “rise up” the wooden walls through 50cm (20 inches) of gravel, 14cm (5.5 inches) of insulation, and 30cm (12 inches) of waterproof concrete. But all the construction professionals involved insisted on it, arguing that otherwise water contained in the base plate could penetrate through the floor structure into the walls or finishes and cause damage (or something similar). And I didn’t want to be the only one to keep arguing about it for days over €1500 (as sometimes happens, as mentioned by someone else elsewhere, you lose the proper perspective on money).
In short: Yes

I couldn’t understand it either, but we went ahead and did it. But why is it acceptable not to apply a waterproofing barrier in the upper floor? Why can’t the water contained in the concrete slab there damage the finishes? Did anyone give you an explanation for that?

No concrete ceiling on the upper floor 😎, instead a 16cm (6.3 inches) wooden ceiling.

Hello,

the sealing membrane is actually intended to prevent the residual moisture in the concrete from entering the building and is not a waterproofing layer against external water. The reason for this is that the slab cannot dry out to the outside and therefore the moisture can only escape inward. For a floor slab between stories, this is not necessary because the drying process can take place downward. It is therefore more of a vapor diffusion retardant layer. However, I agree that opinions vary regarding the usefulness of this, but it is generally accepted as standard practice in the industry.

Best regards