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
B
Benutzer 100330 Mar 2018 11:30Hello forum,
The penetrating moisture can only have a few possible causes:
- Tap water leak: Test with the water meter is negative, but theoretically there could still be a leak before the water meter.
- Backflow of wastewater: Wastewater always smells, so this is probably negative. The upcoming sewer inspection will provide clarity.
- Heating system leak: If the pressure in the heating system remains constant, it is tight. I assume this point has already been considered—negative.
- Condensation moisture: The dew point is not being reached—negative.
- Faulty roof drainage: The moisture flows evenly in all weather conditions—negative.
- Penetrating moisture from the ground: Even if the structure was built as a “white tank” (watertight concrete), the seal has not been proven. Penetrating moisture can flow in evenly.
If the sewer inspection does not reveal anything (which I assume), in my opinion, only penetrating moisture from the ground remains as an explanation. Otherwise, the even flow of water cannot be explained.
The cause is therefore likely somewhere within the structure itself, or in the area of below-ground wall penetrations (electrical, water, wastewater pipes, etc.).
A leaking wall penetration can be relatively easily repaired once accurately located.
If the problem lies in the building structure itself, you are likely facing an extensive renovation.
Good luck and best regards
Kristof
The penetrating moisture can only have a few possible causes:
- Tap water leak: Test with the water meter is negative, but theoretically there could still be a leak before the water meter.
- Backflow of wastewater: Wastewater always smells, so this is probably negative. The upcoming sewer inspection will provide clarity.
- Heating system leak: If the pressure in the heating system remains constant, it is tight. I assume this point has already been considered—negative.
- Condensation moisture: The dew point is not being reached—negative.
- Faulty roof drainage: The moisture flows evenly in all weather conditions—negative.
- Penetrating moisture from the ground: Even if the structure was built as a “white tank” (watertight concrete), the seal has not been proven. Penetrating moisture can flow in evenly.
If the sewer inspection does not reveal anything (which I assume), in my opinion, only penetrating moisture from the ground remains as an explanation. Otherwise, the even flow of water cannot be explained.
The cause is therefore likely somewhere within the structure itself, or in the area of below-ground wall penetrations (electrical, water, wastewater pipes, etc.).
A leaking wall penetration can be relatively easily repaired once accurately located.
If the problem lies in the building structure itself, you are likely facing an extensive renovation.
Good luck and best regards
Kristof
Did you have a soil investigation carried out before the start of construction? What were the results?
For the analysis of any type of samples: laboratories are well aware of what to test for if the problem is clearly described. If necessary, send comparison samples as well, such as tap water, rainwater, or soil samples, to help rule out possible causes.
For the analysis of any type of samples: laboratories are well aware of what to test for if the problem is clearly described. If necessary, send comparison samples as well, such as tap water, rainwater, or soil samples, to help rule out possible causes.
Prefabricated wall panels do not automatically mean a waterproof concrete shell. Conveniently, the structural contractor went bankrupt and the house was self-built, water stood in the excavation pit ... this certainly raises some suspicion.
Soil survey – I think you can guess the likely outcome given the situation.
Soil survey – I think you can guess the likely outcome given the situation.
So, I’m getting back in touch after several inspections were carried out.
I invited a friend to inspect the sewer pipes with a camera -> everything was tight and without any problems.
He advised me to notify my building insurance and take appropriate action.
I did that and was asked to hire a leak detection company.
The company arrived the next day. First, the technician shut off the main water supply for about 1 minute. Then he turned it back on immediately. At first, you could see the small dial running until it stopped again.
This means that the pipe with the leak initially released pressure and then, after reopening the line, water flowed back in.
We then went into the basement apartment. As if he knew, the technician went to the kitchen and checked the water pipes under the sink, and sure enough, the water supply to the washing machine had a leak. It wasn’t tightened properly, so water ran down the pipe onto the floor slab. The technician explained that the water meter doesn’t start moving until the flow rate is at least 10 liters per hour (2.6 gallons per hour).
As a precaution, a pressure test was conducted on the pipes afterward; everything was tight. The water connection was tightened, and the problem was resolved.
After the leak detection, my insurance asked me to arrange for drying, which I did immediately.
Possibly, the tenant’s liability insurance will be held responsible since he caused the damage.
Thanks again to everyone for the support and help.
I invited a friend to inspect the sewer pipes with a camera -> everything was tight and without any problems.
He advised me to notify my building insurance and take appropriate action.
I did that and was asked to hire a leak detection company.
The company arrived the next day. First, the technician shut off the main water supply for about 1 minute. Then he turned it back on immediately. At first, you could see the small dial running until it stopped again.
This means that the pipe with the leak initially released pressure and then, after reopening the line, water flowed back in.
We then went into the basement apartment. As if he knew, the technician went to the kitchen and checked the water pipes under the sink, and sure enough, the water supply to the washing machine had a leak. It wasn’t tightened properly, so water ran down the pipe onto the floor slab. The technician explained that the water meter doesn’t start moving until the flow rate is at least 10 liters per hour (2.6 gallons per hour).
As a precaution, a pressure test was conducted on the pipes afterward; everything was tight. The water connection was tightened, and the problem was resolved.
After the leak detection, my insurance asked me to arrange for drying, which I did immediately.
Possibly, the tenant’s liability insurance will be held responsible since he caused the damage.
Thanks again to everyone for the support and help.
C
chand19863 Apr 2018 13:45Thank you for the report.
As is often the case in life, after a lot of guesswork and increasingly complex thought processes, the most simple solution turns out to be the right one...
However, I don’t quite understand the water meter and the reading in L/min. Doesn’t it show the total consumption?
If it had moved even slightly during a night when no one used the bathroom, wouldn’t a pipe issue have been immediately obvious?
As is often the case in life, after a lot of guesswork and increasingly complex thought processes, the most simple solution turns out to be the right one...
However, I don’t quite understand the water meter and the reading in L/min. Doesn’t it show the total consumption?
If it had moved even slightly during a night when no one used the bathroom, wouldn’t a pipe issue have been immediately obvious?
chand1986 schrieb:
I don’t quite understand the water meter and the reading in L/min. Doesn’t it show the total consumption?
No, water meters are not calibrated for very small amounts. Unfortunately, I don’t know the exact flow rate threshold that must be exceeded for the meter to register. I only know from aquarium keeping that aquarium water is continuously refilled in "droplet-sized" amounts so that the water meter does not register any usage.
Similar topics