Concrete floor levels and prep for parquet

[malcolm]

I bought 52m2 of parquet for a lockdown project - it's 20mm oak. The floor once had 35mm pitch pine parquet but that was mostly removed in the '70s and the floor was levelled with a very weak cement mix that is easy to remove. The original floor beneath is 1920s cement on earth less than 2 inches thick. I think the floor falls 2 inches from one end to the other and I'm keen to level it before adding the parquet. If I chip away the weak concrete to get back to the original floor I'll still need to raise the floor by around 15mm to get back to level.

I'm happy with an impermeable floor and can make the parquet and walls work with that. It would be nice to insulate a bit as it's the main room in the house and it does get heated. But the house was built before foundations were invented - one end is 1600 and the other built on an 1800 outbuilding. so I don't have much depth to work with.

I'm struggling to come up with a good solution.

 

[a twig]

Do you have to level it? A 2” fall might not be the end of the world across a large enough room?

 

[a twig]

15mm is well within the range of most modern self levelling compounds if you don’t have any objection to using them?

There are also insulating ones like this

https://proofshield.co.uk/product/prooftherm-insulating-screed/