ᐅ Lateral waterproofing of the foundation slab

Hello everyone,

I want to waterproof the foundation slab myself on the side and, due to material availability, order it early.
The house manufacturer finishes the house on the slab with an aluminum Z-profile that extends 10cm (4 inches) beyond the slab. The prefabricated walls rest on swelling mortar and are waterproofed downward against the slab to prevent water, pests, etc.

Insulation of 6cm (2.4 inches) with thermal conductivity class 40 still needs to be installed. This should be sealed upward toward the aluminum Z-profile using compressible sealing tape. First question: For the insulation, should I use EPS, XPS, or something else entirely?

The site manager said there should be a waterproofing layer between the insulation and the slab (though many omit this). Would you waterproof here, and if so, how?

Regards,
sciliar

Hello,

I didn’t quite understand that.
Could you draw it out?
Is the waterproofing applied to the outside edge of the foundation slab or across the entire surface? Where should the insulation go?

Best regards,
Jann

Hi,

I'm not really a painter :-)
This is only about the lateral waterproofing. The base slab is finished, and a prefabricated house will be placed on it. The upward waterproofing is handled by the prefab house manufacturer during installation, sealing around the edge of the base slab up to 5cm (2 inches) from the top along the side. The house extends 9cm (3.5 inches) beyond the base slab; a Z-shaped aluminum profile will be installed underneath the house for covering. On site, we need to install the continuous 6cm (2.5 inches) thick perimeter insulation on the side, sealing it at the top with compressible sealing tape against the Z-profile. The question is: does an additional waterproofing layer need to be applied between the lateral perimeter insulation and the base slab, and if so, how (bitumen, waterproof slurry, etc.)? The house manufacturer said it can be done, but it is not necessary.

Ah, okay – understood...
Question 1 – XPS or EPS → XPS
Question 2 – Extending the waterproofing by 5 cm (2 inches) onto the side of the panel is not sufficient. Of course, it depends on how much water pressure there actually is. Therefore, I would recommend installing a waterproofing layer. Regarding what material to use for the waterproofing, the first question is again how much water to expect (soil survey?).
Presumably, it is just ground moisture there, right?

The house manufacturer will probably weld a bitumen membrane onto the panel. Then you need a waterproofing that is compatible with bitumen membranes and that you are able to install.
The best option would be to weld on another bitumen membrane, but if you can’t do that, I would use a thick bitumen coating.

You can always say “it’s not necessary” – but when it comes to waterproofing, I’d rather spend a bit more money now than find out in 10 years that it was not enough.

Ah, an additional note: The slab is only 16 cm (6 inches) thick and does not sit fully underground, only the lower 9 cm (3.5 inches), and that only on two sides (one side is the carport, which will be paved, the other side is on a slight slope). The plaster will be applied over the XPS insulation boards, and then this will form the base from the ground. Alternatively, we are considering attaching a row of slate instead of plaster, but we are unsure how to fix slate onto XPS.

Hmm, okay, instead of XPS you could also use special EPS base boards, but I still recommend XPS with a textured surface; otherwise, the plaster won’t adhere properly. The plaster should also act as a moisture barrier – well-known manufacturers offer products that are usually called something like Flexyl. If you build it up like that with Flexyl on the outside, you can also apply a mineral waterproof slurry onto the board.