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I have a big hole in my kitchen floor (inserting a beam and post to take down a load bearing wall), and I'm now left with having to fill this hole (after dumping around 300 mm of concrete on the post footing).

Hole in concrete floor

It's a floating concrete floor and the hole is right between two of the concrete beams (500 mm apart). On each beam there is a small (20 mm) lip. The floor is beam and block (except instead of blocks it's just polystyrene insulation blocks) with the concrete poured on top.

I've heard two suggestions on how to fix the hole:

1) Cut the edges of the hole clean, then cut and put a 40/50 mm thick concrete slab (council slab) on the lip, DPM, celotex insulation 100/80mm, another DPS sheet, and then 40-50 mm of concrete (with mesh) on top.

2) There is about 400 mm of air between the ground and the bottom of the floor. dump hardcore in the hole until it's level with the floor, then basically just add a bunch of concrete and the 100 mm insulation.

concrete floor hole from the side

I'm putting laminate flooring (so I'm doing a DMP paint, and then adding plastic DMP sheeting) and would like to not have to wait forever for a very thick layer of concrete to dry out (which could take months), as we are eager to start working on making the room habitable.

I'm a bit worried that the 20 mm lip supporting the concrete slab (Option 1) will cause a very high load along the middle of the slab, which might cause it to snap like a KitKat. Maybe adding the hardcore (Option 2) would be a good idea to support the slab? or having a steel plate cut?

Any suggestions or comments will be appreciated.

  • Is it necessary that the hole cover be concrete? ad structure to support a slab of wood? – Alaska Man Feb 17 '18 at 17:48
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This is how I ended up solving it, maybe this will help someone in a similar situation out.

After talking to the building regulations guys, I ended up fixing this hole using alternative 1 above (more or less).

A 40mm concrete slab was cut and placed in the hole, standing/jumping on it seemed very solid.

Hole filled with concrete slab

Added 80mm insulation on top of the slab and in the gaps on the sides so the concrete doesn't just run down into the hole.

Ten put down a damp proof membrane sheet before pouring 40-50mm concrete on top (no mesh needed). Building regulation guy suggested 60-70mm thick concrete on top as that would not crack as easy, but 40-50mm was fine

Concrete filled hole

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