ᐅ Foundation Waterproofing Missing – Recommended Actions?

Hello everyone,

At our house built in 2010, we noticed a few centimeters above the terrace stones that the plaster is efflorescing. Digging around all four exterior sides revealed that the waterproofing layer made of bitumen, shown on the construction drawings between the foundation and the masonry, is missing. Regardless of the cause, responsibility, fraud, or whatever else, I would like to inquire about the necessary work to be done here. The opinions I've received so far vary widely.

Here is how I currently assess the required work:

• Expose the foundation all around (This can be done by oneself – including breaking through the door portal. But how deep? According to the drawings, the waterproofing must extend to 20cm (8 inches) below the top edge of the foundation. Is that sufficient? Is it also necessary to waterproof from the inside, meaning beneath the strip footing up to under the supported slab?)
• Drying time (How long? If the masonry and plaster are really damp, this should be factored in, right?)
• Waterproofing (Priming, applying bitumen membrane from a roll or similar, possibly multiple layers. Can this be done by oneself, or should a professional company be hired?)
• Backfilling and everything should be fine...

Regarding point 4: that’s at least what I hope. About me: I enjoy doing things myself but am more into mechanical tinkering. And, of course, time...

I look forward to your answers and thank you in advance.

Best regards

vaincare

Hello and welcome to the house construction forum.

I’m having some trouble understanding your text. Are you referring to the waterproofing between the foundation slab and the first course of blocks (horizontal)? Or is it about the waterproofing of the exterior wall (vertical)?

I recommend consulting an expert or a specialized contractor to agree on the necessary measures. In this forum, only advice can be provided. The actual implementation usually depends heavily on the specific house and construction method.

Hello Jochen,

thank you very much for your quick and kind response. The issue concerns the vertical waterproofing of the exterior wall.

The house itself is built on strip foundations, with a concrete slab poured on top (no basement). The masonry is made of aerated concrete blocks on the strip foundations; the exterior wall is plastered—and as mentioned above, it is efflorescing.

We have already had three experts on site. The first said: simply renew the exterior plaster—done. The second said: excavate all around, cover with bituminous coating, backfill—done. The third recommended something similar to the second, but wanted to inject synthetic resin—which I believe is not suitable in this case. Therefore, I no longer fully trust the experts. One might ask, what are they good for anyway?

Best regards

vaincare

It’s the same for us: strip foundation, ground slab, and then aerated concrete.

Our bricklayers sealed the ground slab and the lowest row of blocks with waterproof slurry.
After the base coat plaster was applied, I then applied three layers of waterproof slurry from the foundation over the ground slab up to 15cm (6 inches) above the planned finished ground level.
The base render will be applied over that at some point.

By the way, the lower part of the base coat plaster is also a special type of plaster. Unfortunately, I don’t have a name for it.

@vaincare: Do you have any pictures? Your description is missing the insulation.

Pictures would indeed be helpful.

Insulation is not necessarily required for aerated concrete.