Water stain in the basement. Seal the waterproof membrane and perimeter insulation?

Hello everyone,

when it rained heavily last week, I noticed a small water stain in our basement. Primer for the bitumen sealing membrane as well as perimeter insulation have been applied. However, it has only been filled up to about half so far. This small water stain is located almost exactly at the level of the earth filled in so far. What could have gone wrong there? Presumably, water has gotten between the masonry and the bitumen sealing membrane? How is something like this professionally sealed? I hope the pictures show what I mean! Is it possible that water has gotten between the individual layers? In one of the pictures, sealing slurry has already been partially applied. Partly not. Are finishing strips normally installed there?

Hello,

to your question, first some basic questions need to be clarified:

1. Which welding membrane was used and by which method was it applied? Meaning fully glued over the entire surface or glued only at specific points. (We can talk about right or wrong afterwards)
2. What was required? Is the water level always to be expected like this? In other words, is the basement "occasionally" flooded like here? presumably yes.
3. What happens to the area that has no sealing and no insulation yet? Will something still be built there or does it still have to be sealed?

Assuming that 1. a welding membrane and not a cold self-adhesive bitumen membrane was used and that the retained area will still be sealed and insulated, I would assume here that the execution was not professional and therefore a backflow under the bitumen membrane can occur.

Why is that so?

Bitumen membranes must be applied with sufficient overlap in both vertical and horizontal joints. I cannot assess the vertical, but horizontally it is no longer achievable here due to the existing insulation. If it is a bitumen membrane that is "welded on" with a torch, the connection to the insulation cannot be made without either damaging the insulation or not properly ensuring the bond to the wall. Because then he only heated and stuck the membrane. A sure sign of a good adhesion is bitumen oozing out at the outer edges; then it has been heated enough and pressed on with enough pressure. This is not visible here.

If it is a cold self-adhesive membrane (KSK), the above-mentioned points, except for the overlaps, must be considered somewhat differently. However, I am personally very cautious with a KSK. I have an expert report stating that the expert could not reliably prove that a KSK can ensure permanent protection against underflow. This would deny the equivalence between KSK and bitumen welding membrane. If I have the choice, I decide against a KSK.

But to answer more specifically here, I will first wait for the answers to the above 3 questions. I can then gladly show you photos of how a pressure-waterproof sealing using bitumen is professionally made, if this should be the requirement here.

Until then, good luck,

Jann