ᐅ Proper Waterproofing of Basement Slabs. What Are the Alternatives?
Created on: 15 Jul 2011 12:17
D
derNeugeBauerD
derNeugeBauer15 Jul 2011 12:17Hello,
now that the water damage in our basement is being repaired — meaning the damp screed, underfloor heating, and insulation are being removed — we plan to waterproof the basement floor slab as a precaution.
A few facts:
House built in 1999
Almost 100 m² (1,076 sq ft) basement
Underfloor heating in the basement (total floor construction about 17 cm (7 inches) so far and planned again)
Clayey soil
Load case according to DIN 18195 – rising seepage water
Drainage all around the house
Floor slab 20 cm (8 inches) thick (not waterproof concrete)
Below that a 15 cm (6 inches) blinding layer / sand / gravel
Basement exterior walls: 36.5 cm (14 inches) Poroton bricks, outside with thick bitumen coating and perimeter insulation
Above the first brick row: R500 bitumen membrane
Below the first brick row: flexible sealing slurry
Maximum groundwater level reportedly 50 cm (20 inches) below the top of the floor slab
The basement is not used as a storage cellar for vegetables.
The underfloor heating will be reinstalled. For now, the basement will be used as a party and guest room. In a few years, possibly as a separate apartment or for our son.
I have collected some offers from roofers, masons, and others, but every contractor proposes a different method to waterproof the slab.
Maybe you can exclude some methods or even recommend one.
It should be reasonably cost-effective if possible. I have sorted the (current) offers from cheapest to most expensive.
Offer 1:
Single layer of Knauf Katja Sprint waterproofing membranes with overlaps on the floor slab
Edge areas glued to the slab with bitumen adhesive at the masonry walls
Edge at the first brick row sealed with flexible sealing slurry and then raised with Katja Sprint
Corners glued cold with Knauf connection strips
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 2:
4 mm (0.16 inches) flexible sealing slurry applied to the floor slab
Carried up to the first brick row
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 3:
Single layer of V60 S4 (+AL?) welded with overlap on the floor slab
Carried up to the first brick row
Edge area previously additionally sealed with sealing slurry
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 4:
Cold bitumen primer on the floor slab
Then a single layer PYE 200 S5 talcum-coated, welded with overlaps
Carried up to the first brick row
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 5:
Hot bitumen on the floor slab
Foam glass (exact thickness and type not yet specified)
Foam glass glued with hot bitumen up to the edge area
Covered with a V60 S4 membrane
On top: 1 layer of ?? cm polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Regarding offer 5, the roofer mentioned he hasn’t used this method before but would recommend it. He said he would get back to me with detailed planning, execution, and pricing. Due to the high material cost, he is sure it will be the most expensive option.
When I asked about possible condensation forming at the edge of the insulation and thus the creation of a condensation pocket under the insulation, one mason suggested placing 5 cm (2 inches) polystyrene on the slab, then Knauf Katja Sprint, and then another 5 cm (2 inches) of polystyrene on top. No exact execution details were given here either. He said he would pass this information to a roofer friend who will contact me.
I hope you can share your (constructive) input.
Thanks in advance!
now that the water damage in our basement is being repaired — meaning the damp screed, underfloor heating, and insulation are being removed — we plan to waterproof the basement floor slab as a precaution.
A few facts:
House built in 1999
Almost 100 m² (1,076 sq ft) basement
Underfloor heating in the basement (total floor construction about 17 cm (7 inches) so far and planned again)
Clayey soil
Load case according to DIN 18195 – rising seepage water
Drainage all around the house
Floor slab 20 cm (8 inches) thick (not waterproof concrete)
Below that a 15 cm (6 inches) blinding layer / sand / gravel
Basement exterior walls: 36.5 cm (14 inches) Poroton bricks, outside with thick bitumen coating and perimeter insulation
Above the first brick row: R500 bitumen membrane
Below the first brick row: flexible sealing slurry
Maximum groundwater level reportedly 50 cm (20 inches) below the top of the floor slab
The basement is not used as a storage cellar for vegetables.
The underfloor heating will be reinstalled. For now, the basement will be used as a party and guest room. In a few years, possibly as a separate apartment or for our son.
I have collected some offers from roofers, masons, and others, but every contractor proposes a different method to waterproof the slab.
Maybe you can exclude some methods or even recommend one.
It should be reasonably cost-effective if possible. I have sorted the (current) offers from cheapest to most expensive.
Offer 1:
Single layer of Knauf Katja Sprint waterproofing membranes with overlaps on the floor slab
Edge areas glued to the slab with bitumen adhesive at the masonry walls
Edge at the first brick row sealed with flexible sealing slurry and then raised with Katja Sprint
Corners glued cold with Knauf connection strips
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 2:
4 mm (0.16 inches) flexible sealing slurry applied to the floor slab
Carried up to the first brick row
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 3:
Single layer of V60 S4 (+AL?) welded with overlap on the floor slab
Carried up to the first brick row
Edge area previously additionally sealed with sealing slurry
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 4:
Cold bitumen primer on the floor slab
Then a single layer PYE 200 S5 talcum-coated, welded with overlaps
Carried up to the first brick row
On top: 2 layers of 5 cm (2 inches) polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Offer 5:
Hot bitumen on the floor slab
Foam glass (exact thickness and type not yet specified)
Foam glass glued with hot bitumen up to the edge area
Covered with a V60 S4 membrane
On top: 1 layer of ?? cm polystyrene, film, underfloor heating, and 6 cm (2.5 inches) cement screed
Regarding offer 5, the roofer mentioned he hasn’t used this method before but would recommend it. He said he would get back to me with detailed planning, execution, and pricing. Due to the high material cost, he is sure it will be the most expensive option.
When I asked about possible condensation forming at the edge of the insulation and thus the creation of a condensation pocket under the insulation, one mason suggested placing 5 cm (2 inches) polystyrene on the slab, then Knauf Katja Sprint, and then another 5 cm (2 inches) of polystyrene on top. No exact execution details were given here either. He said he would pass this information to a roofer friend who will contact me.
I hope you can share your (constructive) input.
Thanks in advance!
B
Bauexperte16 Jul 2011 11:27Hello,
My constructive input is this: quickly involve someone who has the necessary expertise and definitely do not contract the work yourself. If you have no clear understanding of what is right or wrong—and since we do not have detailed knowledge of the building structure, ground conditions, etc., and cannot give reliable advice here—an expert should explain and recommend the correct measures to you. Trying to save money at the wrong stage in such sensitive work can become quite expensive.
Kind regards
derNeugeBauer schrieb:
I hope you all share your (constructive) opinions here
My constructive input is this: quickly involve someone who has the necessary expertise and definitely do not contract the work yourself. If you have no clear understanding of what is right or wrong—and since we do not have detailed knowledge of the building structure, ground conditions, etc., and cannot give reliable advice here—an expert should explain and recommend the correct measures to you. Trying to save money at the wrong stage in such sensitive work can become quite expensive.
Kind regards
D
derNeugeBauer16 Jul 2011 16:33Bauexperte schrieb:
Hello,
My constructive advice is: quickly involve someone with expertise and definitely do not assign the work on your own. If you have no clear idea of what is right or wrong – and since we do not have detailed knowledge of the building structure, soil conditions, etc., we certainly cannot make any recommendations here – an expert should explain and recommend the appropriate measures. Trying to save money on such sensitive work by cutting corners can become quite expensive.
Kind regardsHello Bauexperte,
maybe you missed it, but I HAVE already involved professionals. Everyone seems to have their preferred method of doing things, and among the roofers there is some overlap. I have been presented with several alternatives, which I am sharing here, hoping that someone can advise me on which options I should lean towards and which to avoid.
Details about the building structure and soil conditions are included in the text as well. If there are further questions, feel free to ask.
And please provide any criticism or suggestions for improvement regarding the offers...
B
Bauexperte16 Jul 2011 17:44Hello,
I did read that you have spoken with trade-specific experts and have their quotes in hand. What I meant with my "two cents" was simply that you need someone who can explain the rationale behind the proposed measures based on your house and its specific conditions. Only when you clearly understand the advantages and disadvantages of each option can you make the best decision.
For example, I do not believe that better sealing of the floor slab alone will solve the issue. With rising seepage water, a waterproof masonry structure is always advisable; perimeter insulation and a bitumen thick coating by themselves are not sufficient here. And I would certainly seek an alternative solution instead of relying on a drainage system—that would draw all surrounding water toward your house.
Consult a building surveyor or expert you trust—someone experienced with issues in older houses—and discuss the various options and measures with them. If you rely solely on the contractors’ statements—they likely provide their quotes to the best of their knowledge and belief—you may soon find yourself with water in the basement again despite extensive renovation efforts.
Kind regards
derNeugeBauer schrieb:
Maybe you overlooked it, but I HAVE consulted professionals. Everyone seems to have their preferred method, and among the roofers their opinions overlapped quite well.
I did read that you have spoken with trade-specific experts and have their quotes in hand. What I meant with my "two cents" was simply that you need someone who can explain the rationale behind the proposed measures based on your house and its specific conditions. Only when you clearly understand the advantages and disadvantages of each option can you make the best decision.
For example, I do not believe that better sealing of the floor slab alone will solve the issue. With rising seepage water, a waterproof masonry structure is always advisable; perimeter insulation and a bitumen thick coating by themselves are not sufficient here. And I would certainly seek an alternative solution instead of relying on a drainage system—that would draw all surrounding water toward your house.
Consult a building surveyor or expert you trust—someone experienced with issues in older houses—and discuss the various options and measures with them. If you rely solely on the contractors’ statements—they likely provide their quotes to the best of their knowledge and belief—you may soon find yourself with water in the basement again despite extensive renovation efforts.
Kind regards
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