ᐅ Water on the foundation slab – cause and source of leak unknown
Created on: 21 Mar 2018 10:39
I
ibo85
Hello,
I’m posting here because I’m quite desperate and can’t find a solution to my problem on my own.
Background:
In 2015, I had a house built. I managed the construction myself and hired all the tradespeople directly. Meanwhile, the shell construction company no longer exists — they went bankrupt.
The house has a basement about 2 meters (6.6 feet) below ground level, with approximately 1 meter (3.3 feet) of it above ground.
The slab was poured in one piece. Afterwards, precast wall elements were installed — a “white tank” waterproofing method.
At the time of construction, there was groundwater in the excavation, about 10–20 cm (4–8 inches) high, so still below the slab.
The joints between the precast elements were sealed with bitumen. Metal sheets were installed between the wall and the footing, and in-situ concrete was poured into the precast elements.
About a year after completion, in spring 2016, the interior wall paint peeled off along a horizontal line approximately 20–30 cm (8–12 inches) high and blistered. I hired a company to investigate the problem, but nothing was found. They broke two tiles and checked down to the slab. The slab was slightly damp, but that was all; no cause was found.
Now, nearly two years later, the exact same blisters have appeared on the same wall, and plaster on an exterior wall is wet up to about 1 meter (3.3 feet) high.
I then removed a tile in another spot and broke up the screed down to the slab. There I found about 2 cm (0.8 inches) of standing water. I first removed this water with a wet vacuum cleaner, but this makes no difference, as the water level of about 2 cm (0.8 inches) always returns.
To investigate the cause, I did the following:
1. There is a drainage system around the house with an access chamber that can be opened at ground level. I opened it to check the groundwater level (the drainage is below the slab level) — completely dry, no water at all. However, I have to mention the chamber is located on the opposite side of the house, not where the wall is wet.
Question: Could it be that the groundwater level is higher on the other side of the house? The house is not located on a slope or anything similar.
2. I poured colored dye into the wastewater pipes to see if there is a problem there, then watched the spot in the house where I see the water (the opening). Nothing appeared.
3. I checked the main water meter; it shows only the smallest flow rates, completely still.
4. The basement is heated with underfloor heating. The heating circuit maintains a constant pressure of about 2 bar (29 psi) with no changes.
I’m desperate because I simply can’t be sure where the water is coming from. It is interesting that — no matter how much water I vacuum out — the water level of about 2 cm (0.8 inches) always reestablishes itself. This would suggest groundwater, but the drainage chamber is completely dry, not even damp. No movement on the main water meter, no pressure drop in the heating circuit, no dye found in the wastewater pipes.
Since I just built the house, I’m currently not in a strong financial position. Because the shell contractor went bankrupt, all costs are falling on me.
I would like to hear your ideas and, based on them, start investigating the cause.
At the moment, there is no suspicion that could narrow down the cause, which is why I don’t want to hire a leak detection company. In 2016, they couldn’t find anything either.
I hope you have suggestions or experiences to share on what I could pay attention to in order to find the leak and what is most likely causing it.
Thank you very much in advance for your answers.
Best regards
I’m posting here because I’m quite desperate and can’t find a solution to my problem on my own.
Background:
In 2015, I had a house built. I managed the construction myself and hired all the tradespeople directly. Meanwhile, the shell construction company no longer exists — they went bankrupt.
The house has a basement about 2 meters (6.6 feet) below ground level, with approximately 1 meter (3.3 feet) of it above ground.
The slab was poured in one piece. Afterwards, precast wall elements were installed — a “white tank” waterproofing method.
At the time of construction, there was groundwater in the excavation, about 10–20 cm (4–8 inches) high, so still below the slab.
The joints between the precast elements were sealed with bitumen. Metal sheets were installed between the wall and the footing, and in-situ concrete was poured into the precast elements.
About a year after completion, in spring 2016, the interior wall paint peeled off along a horizontal line approximately 20–30 cm (8–12 inches) high and blistered. I hired a company to investigate the problem, but nothing was found. They broke two tiles and checked down to the slab. The slab was slightly damp, but that was all; no cause was found.
Now, nearly two years later, the exact same blisters have appeared on the same wall, and plaster on an exterior wall is wet up to about 1 meter (3.3 feet) high.
I then removed a tile in another spot and broke up the screed down to the slab. There I found about 2 cm (0.8 inches) of standing water. I first removed this water with a wet vacuum cleaner, but this makes no difference, as the water level of about 2 cm (0.8 inches) always returns.
To investigate the cause, I did the following:
1. There is a drainage system around the house with an access chamber that can be opened at ground level. I opened it to check the groundwater level (the drainage is below the slab level) — completely dry, no water at all. However, I have to mention the chamber is located on the opposite side of the house, not where the wall is wet.
Question: Could it be that the groundwater level is higher on the other side of the house? The house is not located on a slope or anything similar.
2. I poured colored dye into the wastewater pipes to see if there is a problem there, then watched the spot in the house where I see the water (the opening). Nothing appeared.
3. I checked the main water meter; it shows only the smallest flow rates, completely still.
4. The basement is heated with underfloor heating. The heating circuit maintains a constant pressure of about 2 bar (29 psi) with no changes.
I’m desperate because I simply can’t be sure where the water is coming from. It is interesting that — no matter how much water I vacuum out — the water level of about 2 cm (0.8 inches) always reestablishes itself. This would suggest groundwater, but the drainage chamber is completely dry, not even damp. No movement on the main water meter, no pressure drop in the heating circuit, no dye found in the wastewater pipes.
Since I just built the house, I’m currently not in a strong financial position. Because the shell contractor went bankrupt, all costs are falling on me.
I would like to hear your ideas and, based on them, start investigating the cause.
At the moment, there is no suspicion that could narrow down the cause, which is why I don’t want to hire a leak detection company. In 2016, they couldn’t find anything either.
I hope you have suggestions or experiences to share on what I could pay attention to in order to find the leak and what is most likely causing it.
Thank you very much in advance for your answers.
Best regards
From your description of the drainage, I understand that it goes around the entire house. Pipe cleaning companies have cameras they use to inspect wastewater pipes. You could have one of them come and check the drainage to see if there is water on the relevant side. This should not cost more than 200€ (about $220). Then you can consider this as a possible cause or rule it out.
niri09 schrieb:
I’m not an expert, but maybe you could hire a geologist to measure the groundwater level next to the house (possibly even around the entire house). My intuition would lean more towards groundwater, which can also fluctuate.I’ll probably do that at some point if I can’t find any other cause.
Right now, my architect suggests I check whether rainwater is coming down through the two chimney flues, which I find hard to imagine given the amount of water I soak up each time. Does anyone have experience with this—can that much rainwater or condensation accumulate enough to wash away about 2cm (0.8 inches) of the floor slab?
Another possible cause my architect mentioned is that the inspection hatch on the sewer line is faulty and doesn’t open properly, causing wastewater to back up into the house.
I plan to investigate these two points over the weekend.
Does anyone have experience with this?
Good luck with finding the cause; at least you have a chance there. However, it looks like you'll be stuck with all the effort, because:
this sounds quite hopeless. The insolvency administrator holds a fairly comfortable position compared to claimants; they are usually lawyers; and in case of any payout, you must accept that the recovery rate will never be 100%. Often it is so much lower that disputing it is not even worthwhile.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
ibo85 schrieb:
By the way, the shell construction company no longer exists at the moment --> bankrupt.
this sounds quite hopeless. The insolvency administrator holds a fairly comfortable position compared to claimants; they are usually lawyers; and in case of any payout, you must accept that the recovery rate will never be 100%. Often it is so much lower that disputing it is not even worthwhile.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
ibo85 schrieb:
I will probably do that at some point too if I can’t find any other cause.
Now my architect suggests I check whether rainwater is coming down through the two chimney pipes, which I find hard to imagine given the large amounts of water I soak up every time. Does anyone have experience with this? Can so much rainwater or condensation form that the slab is washed out to about 2cm (1 inch)?
Another possible cause the architect mentioned is that the access hatch on the sewer line is defective and doesn’t open properly, causing wastewater to back up into the house.
I will try to investigate both points over the weekend.
Does anyone have experience with this?You can probably take a look inside the chimneys quite easily through the cleaning openings at the bottom. There should be signs of leaking water if that’s the case. But I find that very unlikely. Such a chimney has an opening area of maybe 0.05m² (0.5 sq ft) at the top if a stove is connected… heating systems usually less. With just a few liters of rain per square meter, hardly anything gets in, and that evaporates in the rising warm exhaust gases.
Didn’t you try using colored water in the wastewater? That would have revealed any issue with the backwater valve.
How cold are the slab or basement walls? Are they below the dew point? Otherwise, nothing should be condensing there.
So I’m still guessing groundwater as the cause, even though unfortunately that’s the most difficult and expensive option to fix….
miho schrieb:
You can probably get a good look inside the chimneys through the cleaning openings at the bottom. You should also find traces of water leaking out there. But I find that very unlikely. Such a chimney has an opening area at the top of maybe 0.05m² (0.5 sq ft) if a stove is connected... heating systems usually less. With a few liters of rain per m² (per sq ft), almost nothing gets in, and what does evaporates in the rising warm exhaust gases.Yes, I already checked yesterday, it’s dry. In my opinion, that was too unlikely anyway.
miho schrieb:
Didn’t you try coloring the wastewater? That would have revealed the issue with the backflow valve.I did try coloring it, but looking at the amount of water I’m pumping out, I can imagine the color might be so diluted that it’s no longer detectable.
miho schrieb:
How cold are the floor slab or basement walls? Are they below the dew point? Otherwise, nothing should be condensing there.Well, the floor surface is relatively warm thanks to the underfloor heating. When I checked the damp spots with a thermal imaging camera, those areas were quite cold, but not below the dew point. What exactly are you aiming at?
miho schrieb:
My guess is still groundwater, even though that’s unfortunately the hardest and most expensive option to fix… Yes, unfortunately I also fear that’s exactly the case.
However, I want to have a sewer inspection done before any renovation work, just to avoid unnecessary costs.
If I need to repair, I’m considering a step-by-step approach: first sealing the wall/joint that is currently visibly affected, then gradually more areas until the water stops coming in. I would try to avoid breaking up the screed at those points if possible and maybe use longer drill bits to reach the joint and then do the injection there. According to a knowledgeable friend, that should be possible. But it would be a somewhat blind injection.
Beforehand, I was also advised to possibly drill at the side of the house in the garden to determine the groundwater level.
Still, I can’t explain how something like this could happen within one month. The current tenant living in the basement moved in only at the beginning of February, and the walls were completely dry then. There hasn’t been heavy rain or anything unusual in recent months.
I’m at a loss, thanks so far for your replies. I’m still open to any ideas.
ibo85 schrieb:
Yes, I already checked yesterday and it’s dry. In my opinion, that was very unlikely anyway.Okay, you can already rule that out then.
ibo85 schrieb:
I did try using color, but considering the amount of water I’m pumping out, I can imagine the color might be so diluted that it’s no longer visible.Yes, that is certainly possible. That reminds me: A few years ago, we had a similar case in a multi-family building where we were renting. After a longer search, chemical analyses of the water were carried out to find the cause. By examining impurities, it is apparently possible to identify different sources. It turned out to be the desalination unit.
ibo85 schrieb:
The floor surface is relatively warm due to the underfloor heating. When I looked at the damp spots with a thermal imaging camera, those areas were quite cold but not below the dew point. What exactly are you aiming at?If condensation is supposed to occur, the temperature of a surface in contact with the moist air must be below the dew point. So if all temperatures remain above the dew point, nothing should condense. You could also calculate the air volume and temperature difference required to produce your level of water ingress by condensation. That way, you would know whether such an entry of water by condensation is even plausible.
ibo85 schrieb:
Yes, unfortunately I also fear that this is exactly the case.
However, I want to conduct a sewer inspection before starting any remediation work, just to avoid unnecessary costs.I would do the same.
ibo85 schrieb:
If I do proceed with repairs, I might take a step-by-step approach, meaning first injecting grout into the wall/joint that is currently visibly affected, and then gradually more until I notice that the water no longer comes through. If possible, I want to avoid breaking out the screed in those areas and maybe use longer drill bits to reach the joint for injection, according to a knowledgeable acquaintance. However, that would be somewhat blind grouting.
I was also advised to possibly drill at the side of the house in the garden to determine the groundwater level.
But I still can’t explain how something like this could happen within a month. The current tenant living in the basement just moved in at the beginning of February; back then, the walls were completely dry. There has been neither heavy rain in the past months nor anything else unusual.Such a sudden occurrence is certainly striking. Has the tenant possibly caused any damage during drilling or other works at move-in, whether intentionally or unintentionally?
Does the local weather suggest a rise in groundwater? Or has there been any nearby construction work that diverts groundwater flows or did so until recently?
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