ᐅ Waterproofing of foundation slab for the load case of hydrostatic pressure
Created on: 10 Aug 2025 13:10
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blablubHello everyone,
after the foundation slab was completed, it now needs to be waterproofed against the load case of hydrostatic pressure W.2-1E (we have occasional rising groundwater layers here). The planner roughly specifies fully welding the waterproofing membrane over the entire surface. A PYE Photovoltaik 200 S5 membrane is apparently sufficient here.
The question now is how the installation should be done beneath the masonry.
Two companies—three opinions. One says G 200 DD and to weld it to the surface waterproofing membrane. The other says to apply the surface waterproofing completely over the foundation slab and additionally install the G 200 DD underneath the masonry.
What is correct here?
The planner himself seems uncertain. Unfortunately, I have not found any detailed specification on this so far. Therefore, I hope someone here might be able to help.
Thank you in advance.
after the foundation slab was completed, it now needs to be waterproofed against the load case of hydrostatic pressure W.2-1E (we have occasional rising groundwater layers here). The planner roughly specifies fully welding the waterproofing membrane over the entire surface. A PYE Photovoltaik 200 S5 membrane is apparently sufficient here.
The question now is how the installation should be done beneath the masonry.
Two companies—three opinions. One says G 200 DD and to weld it to the surface waterproofing membrane. The other says to apply the surface waterproofing completely over the foundation slab and additionally install the G 200 DD underneath the masonry.
What is correct here?
The planner himself seems uncertain. Unfortunately, I have not found any detailed specification on this so far. Therefore, I hope someone here might be able to help.
Thank you in advance.
Hi,
for load case W.2-1E, the fully welded PYE Photovoltaic 200 S5 on the concrete slab is generally state of the art. Under the masonry, a layer of G 200 DD is typically installed as a damp-proof membrane. However, this is not welded to the waterproofing layer but laid loose to allow for movement. The waterproofing runs underneath the wall where possible; otherwise, it should be carefully detailed to prevent water from getting behind the barrier layer. Is it specified in detail whether you have a bonded or loose masonry support? That could affect the wall assembly.
Good luck!
for load case W.2-1E, the fully welded PYE Photovoltaic 200 S5 on the concrete slab is generally state of the art. Under the masonry, a layer of G 200 DD is typically installed as a damp-proof membrane. However, this is not welded to the waterproofing layer but laid loose to allow for movement. The waterproofing runs underneath the wall where possible; otherwise, it should be carefully detailed to prevent water from getting behind the barrier layer. Is it specified in detail whether you have a bonded or loose masonry support? That could affect the wall assembly.
Good luck!
So I conclude that the statement from the one company was correct.
Fully weld the ground slab and place an additional layer of G 200 DD under the masonry. But what is the purpose of the cavity barrier here, isn’t the waterproofing membrane alone sufficient?
Regarding the membranes, a PYE 200 S5 should be adequate, but does it matter whether it is polymer- or elastomer-based?
Despite thorough research, I was unfortunately unable to find detailed technical sheets on the installation.
Fully weld the ground slab and place an additional layer of G 200 DD under the masonry. But what is the purpose of the cavity barrier here, isn’t the waterproofing membrane alone sufficient?
Regarding the membranes, a PYE 200 S5 should be adequate, but does it matter whether it is polymer- or elastomer-based?
Despite thorough research, I was unfortunately unable to find detailed technical sheets on the installation.
Hi,
the G 200 DD cavity membrane under the masonry is more than just redundancy. It separates capillary rising moisture from the concrete from the masonry itself. The surface waterproofing protects against hydrostatic pressure, but the standards still explicitly require a horizontal damp-proof course as a moisture barrier within the rising wall. It thus complements the waterproofing beneath the footing. The difference between polymer-modified and elastomeric bitumen is mainly in the application area and long-term flexibility. Do you know exactly how the system compatibility between the membranes is specified by the manufacturer, that is, whether both products are coordinated with each other?
the G 200 DD cavity membrane under the masonry is more than just redundancy. It separates capillary rising moisture from the concrete from the masonry itself. The surface waterproofing protects against hydrostatic pressure, but the standards still explicitly require a horizontal damp-proof course as a moisture barrier within the rising wall. It thus complements the waterproofing beneath the footing. The difference between polymer-modified and elastomeric bitumen is mainly in the application area and long-term flexibility. Do you know exactly how the system compatibility between the membranes is specified by the manufacturer, that is, whether both products are coordinated with each other?
Now I have to ask again because the principle is still not entirely clear to me. So, the cavity barrier membrane is not placed on top of the surface waterproofing but normally lies directly on the concrete slab?
Both membranes would be from the same manufacturer. If necessary, I would check with them again about how this detail is executed, as unfortunately I still cannot find any drawings.
Both membranes would be from the same manufacturer. If necessary, I would check with them again about how this detail is executed, as unfortunately I still cannot find any drawings.
Your question highlights the typical detailing issue very well.
The cavity membrane usually lies directly on the foundation slab before the masonry is built, regardless of the surface waterproofing. It is important that the surface waterproofing extends as far as possible beneath the rising masonry and is tightly connected at the junction, but it should not be rigidly bonded to the G 200 DD. The idea behind this is to stop capillary rising moisture, independent of protection against hydrostatic pressure.
The cavity membrane usually lies directly on the foundation slab before the masonry is built, regardless of the surface waterproofing. It is important that the surface waterproofing extends as far as possible beneath the rising masonry and is tightly connected at the junction, but it should not be rigidly bonded to the G 200 DD. The idea behind this is to stop capillary rising moisture, independent of protection against hydrostatic pressure.
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