ᐅ What should basement exterior walls be coated with?

Hello everyone,

can you recommend a specific product for waterproofing the exterior basement wall? (With or without primer?) At the home improvement store, there are already several products available among bitumen-based coatings (1-component, 2-component...).

This concerns an existing building (the basement is about 1.5 meters (5 feet) below ground level). The basement previously had a black coating, but it is no longer uniformly black. The house stands on a strip foundation about 30 cm (12 inches) wide, and I am wondering whether I should also coat it, since the surface is quite rough, if we are digging around anyway.

Our builder also mentioned that it would be possible to excavate a whole side of the house plus half of another side (including the foundation). Do you not see any issues with that? (I’m curious to hear what our architect will say.)

Hello @Bookstar,

I ordered the WeberSuperflex 10. My receipt from the specialist store also says Superflex 10. However, at home, I noticed that there is Superflex 10 2k (highly flexible) and Superflex 2k (flexible). But I definitely received the cheaper "Superflex 2k," so without the "10."

Let’s see what the store says tomorrow.

I have a few questions about the application. I would appreciate any tips.

1. On the old basement wall, there is still a very thin black layer from the 1960s. During excavation, the excavator operator partially scratched the basement wall (depth approx. 3–4cm (1–1.5 inches)). What do you recommend applying here before the bitumen?

2. To be safe, I want to clean the entire wall with a high-pressure cleaner and then prime it. I’m not sure if I can quickly find a primer tomorrow. Is it problematic to use a primer for thick coatings from a different manufacturer? (That means changing the system.)

3. Unfortunately, our strip footing is only about 30cm (12 inches) deep. On many drainage installations, I’ve seen that the bitumen layer is sometimes applied partly onto the foundation. Is this common? My foundation is very rough, so I probably won’t be able to apply the bitumen smoothly. What would you recommend here?

4. For the soakaway layer, I’m currently leaning towards 8/16 gravel. It is said to be self-compacting. Or would you recommend 2/45 lean concrete and compacting it as well? (Is that even advisable when the drainage pipe is underneath?)

Best regards

Good morning!

Here are my thoughts on the matter.

netzplan schrieb:


1. On the old basement wall, there is still a very thin black layer from the 1960s. During excavation, the excavator operator caused some scratches (depth approx. 3-4cm (1-1.5 inches)) on the basement wall. What would you recommend applying before the bitumen?
Ideally, manually remove as much of the old material as possible.

2. For safety, I plan to clean the entire wall with a high-pressure cleaner and then prime it. I’m not sure if I can quickly find a primer tomorrow. Is it critical if I use a primer for thick coatings from a different manufacturer? (So, switching systems?)
This is not a problem, even though manufacturers often recommend otherwise—they are also interested in profits. The important thing is that it’s really the same type of product. Primer is not just primer. So, pay close attention to ingredients and the intended use or application.

3. Our strip foundation is unfortunately only about 30cm (12 inches) deep. On many drainage installations, I’ve seen that the bitumen layer is partially applied to the foundation as well. Is this common? My foundation surface is quite rough. I probably won’t be able to apply the bitumen properly there. What would you recommend?
I can’t really help without a photo.

4. For the filter layer, I am currently leaning towards 8/16 gravel. It is said to be self-compacting. Or would you use 2/45 mineral concrete and compact that as well? (Is that even a good idea if the drainage pipe is underneath?)
I would also choose gravel, but it’s a matter of cost.

Best regards

Regarding point 1: It will be difficult to remove the old material, that is, the existing bitumen coating. I will do my best. How should I treat the scratches (which can also be partly seen in the next picture) before applying the thick coating here?

Regarding point 3: Here is a picture of the foundation:

Should bitumen also be applied on the side of the foundation? It is very rough. Unless something else is meant to be applied before that. Here is a drainage setup, where many tend to partially seal the foundation as well:

The issue has been resolved. An employee of a specialized company inspected the entire area and recommended sealing approximately 10-15cm (4-6 inches) of the foundation with a thick coating as well. (Before that, the area should be leveled.)