I'm trying to put a sub- and finish floor into a 1920s basement. There is some kind of cement-based topcoat over the original pour. It's strong enough to take a 200 lb point load but not much more. However, it looks like it was troweled with a butter knife. Very uneven, hills and valleys and cliffs, probably a 3" height difference altogether.

Self-leveling compound - would need a LOT

Scribing sleepers - it'd take 20 years

I thought about inserting t-nuts into the subfloor panels and having adjustable feet, with a through-hole so they're accessible from the top, but I'd need 28 per panel (16" OC) and need to grind off their protruding heads when I was done.

And that's all I have for ideas. Anyone run into this and have a neat engineering solution?

thanks,

jim