Hello,
In the basement, a floating cement screed from Knauf was installed. After 5 months, we still have a residual moisture level of 5% – which is far too high.
According to an expert from our Building Owners' Protection Association, there are three possible reasons:
1. The measuring device is faulty (although nothing can be completely ruled out)
2. Insufficient heating and ventilation were provided
3. The waterproof slab is not actually watertight.
The slab is made of waterproof concrete (WU concrete), as is the entire basement, with an additional black tank waterproofing membrane coated with KMB on the outside. During the groundwater lowering, a pump temporarily failed, but the suction was not fully disconnected yet (according to the dewatering company). Therefore, I don’t believe the slab is the issue. Especially since our site manager has experienced drying problems on other construction sites as well.
What do you think?
Regards,
StarAce
In the basement, a floating cement screed from Knauf was installed. After 5 months, we still have a residual moisture level of 5% – which is far too high.
According to an expert from our Building Owners' Protection Association, there are three possible reasons:
1. The measuring device is faulty (although nothing can be completely ruled out)
2. Insufficient heating and ventilation were provided
3. The waterproof slab is not actually watertight.
The slab is made of waterproof concrete (WU concrete), as is the entire basement, with an additional black tank waterproofing membrane coated with KMB on the outside. During the groundwater lowering, a pump temporarily failed, but the suction was not fully disconnected yet (according to the dewatering company). Therefore, I don’t believe the slab is the issue. Especially since our site manager has experienced drying problems on other construction sites as well.
What do you think?
Regards,
StarAce
Hello,
- condensation from warm outside air brought in
- point 3
It is a mistake to assume that WU waterproof concrete is truly waterproof! It is worth reading the relevant DIN standards on this. Certain problems are usually almost inevitable, for example if groundwater lowering is required for basement construction.
This can be taken into account during the design of the building structure in advance.
Also, 100% dry building components do not exist!
Best regards.
StarAce schrieb:He is right here! An explanation can be found by monitoring the moisture development (building component, indoor air) over time. Also, it seems the basement is unheated, so no underfloor heating! Therefore, use a building dryer. If moisture levels rise again after using one, there are usually two reasons:
....
According to our building owners’ protection association expert, there are 3 possibilities:
1. the measuring device is defective (nothing can really be ruled out)
2. insufficient heating and ventilation
3. the waterproof slab foundation is not actually waterproof.
- condensation from warm outside air brought in
- point 3
It is a mistake to assume that WU waterproof concrete is truly waterproof! It is worth reading the relevant DIN standards on this. Certain problems are usually almost inevitable, for example if groundwater lowering is required for basement construction.
This can be taken into account during the design of the building structure in advance.
Also, 100% dry building components do not exist!
Best regards.
B
Bauexperte11 Jun 2013 12:49Hello,
€uro has already made many valid points, although I am not as confident about your expert as €uro seems to be.
As an example, here is an excerpt regarding rising seepage water:
Basement waterproofing
1. According to item 7 Building Waterproofing in the soil report, the load case “Rising seepage water” must be considered for the project according to DIN 18195 T6 A9. The soil surveyor’s recommendation is …
Concrete basements are always a challenge; especially if unheated. Before you look for problems with the supposedly “wrong” screed, check the soil surveyor’s recommendations and, for now, set up drying equipment. Only when it is 100% certain that all requirements from the soil report have been fully met should you proceed with further troubleshooting.
Regards, Bauexperte
€uro has already made many valid points, although I am not as confident about your expert as €uro seems to be.
StarAce schrieb:This sounds more impressive than it actually is. WU simply means “waterproof,” and the so-called “black” tanking system is nothing more than a thick bitumen coating.
The slab is made of waterproof concrete (WU-Beton), as is the entire basement, plus an additional tanking system with a KMB coating on the outside.
StarAce schrieb:You built almost directly in the groundwater and only had to use a standard waterproof concrete basement on a standard waterproof concrete slab without any additional measures? I find that hard to believe! Are you sure that your soil surveyor did not specify any additional waterproofing requirements for the waterproof concrete?
During the groundwater lowering, a pump failed temporarily, but the vacuum was not fully released yet (according to the lowering company). Therefore, I don’t assume the slab is the issue. Especially since our site manager also has problems with drying on other sites.
As an example, here is an excerpt regarding rising seepage water:
Basement waterproofing
1. According to item 7 Building Waterproofing in the soil report, the load case “Rising seepage water” must be considered for the project according to DIN 18195 T6 A9. The soil surveyor’s recommendation is …
Concrete basements are always a challenge; especially if unheated. Before you look for problems with the supposedly “wrong” screed, check the soil surveyor’s recommendations and, for now, set up drying equipment. Only when it is 100% certain that all requirements from the soil report have been fully met should you proceed with further troubleshooting.
Regards, Bauexperte
This is the comment from our construction manager:
- Ground slab according to WU guideline with a thickness of 35 cm (without a blinding layer, but with a Delta membrane with dimples installed on the underside)
- Vertical connection of the ground slab to the double concrete wall elements (thickness = 25 cm (10 inches)) using coated master joint waterproofing sheet
- Filling of the double wall elements with WU concrete with a grain size of 0/8 mm
- Cove fillet with HKS
- Waterproofing of the basement exterior walls using bituminous thick coating in accordance with DIN 18195-6
As already mentioned, the combination of the ground slab design with the waterproofing of the basement walls using bituminous thick coating is not explicitly regulated in the DIN standard but complies with the recognized rules of technology. According to the soil survey, waterproofing as per section 8 of DIN 18195-6:2001-12 is required and must be permanently protected against water ingress from behind. Alternatively, the construction of a watertight basement made of WU concrete is possible (exposure class 1 according to section 5.2 (2) and use class A according to section 5.3 (2), with no masonry exterior basement walls).
- Ground slab according to WU guideline with a thickness of 35 cm (without a blinding layer, but with a Delta membrane with dimples installed on the underside)
- Vertical connection of the ground slab to the double concrete wall elements (thickness = 25 cm (10 inches)) using coated master joint waterproofing sheet
- Filling of the double wall elements with WU concrete with a grain size of 0/8 mm
- Cove fillet with HKS
- Waterproofing of the basement exterior walls using bituminous thick coating in accordance with DIN 18195-6
As already mentioned, the combination of the ground slab design with the waterproofing of the basement walls using bituminous thick coating is not explicitly regulated in the DIN standard but complies with the recognized rules of technology. According to the soil survey, waterproofing as per section 8 of DIN 18195-6:2001-12 is required and must be permanently protected against water ingress from behind. Alternatively, the construction of a watertight basement made of WU concrete is possible (exposure class 1 according to section 5.2 (2) and use class A according to section 5.3 (2), with no masonry exterior basement walls).
B
Bauexperte12 Jun 2013 10:36Hello,
before any false impression arises here – I do not claim to know everything; how could I? Only when it comes to water, especially in basements, do all alarm bells usually go off for me. This is particularly because I encountered a similar situation a few months ago in one of the construction projects we oversee. In that case, the basement contractor simply did not consider it necessary to comply with the specifications from the soil report regarding groundwater pressure.
That is correct:
[LEFT]"There are no DIN standards for the construction of white tanks (watertight concrete structures), but there are standards for the concrete quality and for the structural engineer’s calculations. Furthermore, with the DBV leaflets (German Concrete Association), the DafStb guideline 'Watertight Concrete Structures – 11/2003,' and other recognized printed literature, there is sufficient technical documentation to properly plan and/or assess the correctness of a white tank as a construction method."**
but also:
"Since the publication of the DafStb guideline 'Watertight Concrete Structures – 11/2003,' white tanks are thus considered regulated components. Professionally planned and executed white tanks are recognized rules of engineering best practice."**
** Wording taken from Mark A. Carden from the HwK OWL in Bielefeld, publicly appointed and sworn expert
Therefore, it should be possible, based on the technical literature, to identify the cause of the moisture problem.
Regards, Bauexperte
before any false impression arises here – I do not claim to know everything; how could I? Only when it comes to water, especially in basements, do all alarm bells usually go off for me. This is particularly because I encountered a similar situation a few months ago in one of the construction projects we oversee. In that case, the basement contractor simply did not consider it necessary to comply with the specifications from the soil report regarding groundwater pressure.
StarAce schrieb:
As already mentioned, the combination of the floor slab execution with the waterproofing of the basement walls using bituminous thick coating is not regulated in the DIN standards but does comply with the recognized rules of technology.
That is correct:
[LEFT]"There are no DIN standards for the construction of white tanks (watertight concrete structures), but there are standards for the concrete quality and for the structural engineer’s calculations. Furthermore, with the DBV leaflets (German Concrete Association), the DafStb guideline 'Watertight Concrete Structures – 11/2003,' and other recognized printed literature, there is sufficient technical documentation to properly plan and/or assess the correctness of a white tank as a construction method."**
but also:
"Since the publication of the DafStb guideline 'Watertight Concrete Structures – 11/2003,' white tanks are thus considered regulated components. Professionally planned and executed white tanks are recognized rules of engineering best practice."**
** Wording taken from Mark A. Carden from the HwK OWL in Bielefeld, publicly appointed and sworn expert
Therefore, it should be possible, based on the technical literature, to identify the cause of the moisture problem.
Regards, Bauexperte
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