ᐅ Basement – Combined Waterproofing System Using Both Tanking and Structural Waterproofing Methods

Hello everyone,

according to our scope of work description, the basement is constructed as follows:

"Basement exterior walls are precast double-wall concrete elements, 25 cm (10 inches) thick, backfilled with cast-in-place concrete of waterproof concrete quality. A continuous galvanized and coated joint sheet metal is installed as a connection to the floor slab; the joints are glued and secured with clips. The basement exterior walls are designed as a black tank with a bituminous waterproofing membrane according to DIN 18195-6, as well as perimeter insulation with a thermal conductivity class of 035, 80 mm (3 inches) thick."


If I understand correctly, the double-wall elements provide a white tank waterproofing, and on top of that, there is an additional black tank waterproofing on the outside, right?

Regards,
StarAce

Hello,

Your general contractor/subcontractor (BU/GU) describes their standardized wall construction for a waterproof basement; waterproof means "water-resistant." To make this a "tank" compliant with DIN 18195-6, additional measures must be taken—here described as a plastic-modified bitumen thick coating (KMB).

This means that without considering the soil’s water sensitivity (ground moisture, non-pressurized seepage water, etc.), you would normally get a standard waterproof basement. Only with the additional sealing according to DIN 18195-6 does it become a tank structure.

In my opinion, you seem to have hired a good contractor, as they specifically mention the relevant DIN standard in the contract documents; many would describe this more vaguely.

Best regards

Good, that reassures me. We have constantly pressing water here.

Here is the detailed description of the basement construction:

- Concrete slab according to WU guidelines, 35 cm (14 inches) thick (without a leveling layer, but with a Delta dimple membrane installed underneath)
- Vertical connection of the slab to the precast double-wall concrete elements (thickness = 25 cm (10 inches)) using a coated master joint sealing sheet
- Filling of the double-wall elements with WU concrete with a grain size of 0/8 mm
- Cove fillet with HKS
- Waterproofing of the basement exterior walls with bituminous thick coating according to DIN 18195-6

What do you think about this? Our building expert from the Homeowners’ Protection Association said it is not an unusual solution and acceptable with a very low residual risk – although some residual risk always remains

Hello,

StarAce schrieb:

What do you think about this? Our building surveyor from the Building Owners’ Association said it is not an unusual solution and acceptable with a very low residual risk – however, there is always some residual risk.

I don’t always understand some so-called experts. To eliminate *any* risk, you have to build a true waterproof concrete foundation structure, commonly known as a "white bathtub." This term originally comes from railway construction; first, a basement shell made of waterproof concrete (WU concrete) is poured (after curing, this basement was additionally covered with a light-colored waterproofing membrane, hence the term "white bathtub"), and then the actual basement is built inside it. In other words, a basement within a basement!

If your builder/general contractor follows the recommendations of the soil survey report, that is legitimate and fully sufficient. I also know people who manage to break their finger while picking their nose....

Best regards