ᐅ Concrete slab damp on the underside – what could be the cause?
Created on: 26 Nov 2024 18:46
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Steve55Hello, maybe someone has an idea or can reassure me. It concerns a spot (about 1m (3 feet)) on the ground slab that has remained damp after it has rained (marked in red). The soil that was excavated was immediately removed again, so it couldn’t have come from there, and this was already the case before.
Where it was dry for a longer time, this spot disappeared. Before the house was erected last week, there was a lot of rain and the spot appeared again. After the house stood for a few days, the spot disappeared again. However, it rained heavily again last night, and now a minimal damp area is appearing again, see photos. Inside, at the cutouts for the pipes, it is also damp under the slab, which I noticed earlier. Where could this come from? (I didn’t check if these spots were dry before yesterday’s rain.)
The plumbing company is coming at the end of the week and the screed is scheduled for the end of next week.
I have already spoken with the building expert, and we have to check if water is coming from above, but he can’t say much more at this stage. But I hardly believe that since the house is now sealed. Under the slab there is a 120mm (5 inches) perimeter insulation with foil and a very thick gravel layer (almost 2m (6.5 feet) below that is clay soil) with 5cm (2 inches) coarse gravel, plus frost protection edges. The slab contractor said it might still be residual moisture or condensation.
What do you think? Thanks in advance.
Where it was dry for a longer time, this spot disappeared. Before the house was erected last week, there was a lot of rain and the spot appeared again. After the house stood for a few days, the spot disappeared again. However, it rained heavily again last night, and now a minimal damp area is appearing again, see photos. Inside, at the cutouts for the pipes, it is also damp under the slab, which I noticed earlier. Where could this come from? (I didn’t check if these spots were dry before yesterday’s rain.)
The plumbing company is coming at the end of the week and the screed is scheduled for the end of next week.
I have already spoken with the building expert, and we have to check if water is coming from above, but he can’t say much more at this stage. But I hardly believe that since the house is now sealed. Under the slab there is a 120mm (5 inches) perimeter insulation with foil and a very thick gravel layer (almost 2m (6.5 feet) below that is clay soil) with 5cm (2 inches) coarse gravel, plus frost protection edges. The slab contractor said it might still be residual moisture or condensation.
What do you think? Thanks in advance.
Steve55 schrieb:
Concrete slab damp on the underside – what could be the cause? To help future readers or anyone willing to assist once your thread history grows longer, it would be best if you linked the previous threads yourself – I’ll do this for you now:
https://www.hausbau-forum.de/threads/pfusch-bei-erdarbeiten-baugrube-bis-ins-grundwasser.47815/
https://www.hausbau-forum.de/threads/geo-textilvlies-bei-gruendung-falsche-robustheitsklasse-grk.47837/
https://www.hausbau-forum.de/threads/drainage-laut-bodengutachten-aber-wie.47852/
By the way, providing a bit more explanation about the pictures shared here wouldn’t hurt.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Hello, thank you, but I doubt that this is related. During the groundwork, it was confirmed that everything is fine, and the other two contributions also supported this. The geotextile at this depth can be neglected, and the drainage has become unnecessary in my case since I chose frost skirts.
A brief note on this post:
My slab contractor says the water is not a concern.
A brief note on this post:
My slab contractor says the water is not a concern.
D
derdietmar27 Nov 2024 14:10Hello,
was a membrane installed between the insulation and the concrete (slip layer)? You can catch a glimpse of membrane around the pipe openings. Water can also penetrate from the other side and flow between the slab and the insulation up to this point.
What I find much more concerning are the openings themselves. The slab is interrupted there. How is that supposed to be sealed? Normally, pipes are grouted into the slab using appropriate end fittings.
Best regards
was a membrane installed between the insulation and the concrete (slip layer)? You can catch a glimpse of membrane around the pipe openings. Water can also penetrate from the other side and flow between the slab and the insulation up to this point.
What I find much more concerning are the openings themselves. The slab is interrupted there. How is that supposed to be sealed? Normally, pipes are grouted into the slab using appropriate end fittings.
Best regards
Hello, yes, the membrane was installed over the entire surface. Okay, thanks, but water from below wouldn’t be a concern, right? That’s also what Glatthaar stated. From above it is almost impossible now, since as far as I have checked, everything inside the house is sealed and the area around the slab is dry.
Yes, the cut-outs were discussed again with my builder and the concrete slab contractor, and this is standard practice with this company. I also just saw several slabs done this way in the company’s housebuilding forum. These cut-outs will be sealed again with special waterproofing.
Best regards and thank you.
Yes, the cut-outs were discussed again with my builder and the concrete slab contractor, and this is standard practice with this company. I also just saw several slabs done this way in the company’s housebuilding forum. These cut-outs will be sealed again with special waterproofing.
Best regards and thank you.
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