Fixing sloping cracked concrete floor

[HarryBoyHere]

Hi all
Hope to obtain some advice on the following:
In our first floor flat the kitchen floor is quite uneven and has a slope.
The height difference between one end and the other is 2".
The surface is concrete and has some cracks in the middle.
We've investigated by removing some concrete and found it was originally poured over floorboards. It seems the floorboards look OK .. no evidence of them being uneven.
I see two ways to fix this-
1. Pour on self leveller or screed to level up the floor. Will end up with a bit of a step up into the kitchen.
2. Remove the concrete and put down plyboard over the existing floorboards.

The plan is to replace the kitchen units and lay vinyl tiles so the ply will be needed either way.

I am unsure whether it is a good idea to do 1 because of the extra weight that will be added as a result. I have to consider there is a neighbour's kitchen below.
If I do 2 I am not sure what I might discover once all that concrete is removed!

Any thoughts appreciated. I am attaching a photo showing the partial excavation of the concrete.

 

[Steve]

I would strongly recommend getting a builder in to look at that. There may be a reason for the concrete for fire or sound resistance, but its certainly unconventional, and unreinforced concrete on a flexible wooden floor is never going to last long and IMO it needs sorting out. How thick is it? On your picture it looks like theres a gap under it.

 

[HarryBoyHere]

Hi Steve. I did get a builder in to look at it. He was the one who put the hole in the concrete to take a look underneath. He was mystified as to why concrete had been laid over floorboards in the first place. I also had a 2nd builder come to take a look who was similarly unsure why the floor would have been done this way. The flat is of similar design and age to most of the others in the area (about 100 years old) and the builders, who know the flats, don't usually see concrete floors like this. So I doubt it was done for fire or sound insulation because if that was the case, it's likely the other flats would have similar construction.

At the end where the photo was taken (the lower end) the concrete is quite thin, probably just 1cm, and you're right there is a gap there between the concrete and the floorboards below. I think it is thicker the other end - it must be as the kitchen floor is higher at that end. From what I can see it may be reasonably easy to pry up, especially in the areas where it has cracked.