ᐅ How to close an opening for a wall box?

Hello everyone,

A hole was made through the cavity wall for our downdraft extractor fan.

Questions:

What is the best way to seal the hole, both from the outside and the inside?

These options come to mind:

- Foam? If so, is there a special type?
- Styrofoam?
- Mortar?
- Plaster?

I also read somewhere that a compression tape should be used for the wall box, but that might be a bit tight.

The screed has already been installed.

I can only contribute to a limited extent. I’m installing the wall box this weekend.
It will be filled with construction foam, and the plasterer will handle the rest.

However, I have a quick question. Did you place the rectangular duct directly on the raw floor slab, or did you put anything underneath it/insulate it?

face26 schrieb:

Just a quick question. Did you lay the flat duct directly on the raw floor slab, or did you place/insulate something underneath it?

The duct was installed on the waterproofing membrane, with a thin layer of foam in between to help the base vent fit better.

tumaa schrieb:

The duct was placed on the waterproofing membrane, with a thin layer of foam in between, so the base vent should fit better.

Thanks, but I didn’t fully understand or maybe we’re talking past each other.

I wasn’t referring to the wall box but to the installation of the duct all the way to the point of use. In one photo, it looks like you laid it directly on the floor without anything underneath. My kitchen installer mentioned insulation, and the architect said you can place something underneath. When I asked what exactly, opinions ranged from thin polystyrene to some type of fleece. I’ve also often heard that it’s not necessary.
Now I’m a bit unsure about what to do.