I've researched this extensively without a clear conclusion, so time to reach out to the people who have probably experienced it.
I have a plywood subfloor that has several uneven parts. My plan is to (1) level the worst spots with self-leveling cement; (2) add another half inch layer of flooring plywood glued and nailed to the joists. Then I will felt the remaining uneven spots as necessary, and staple hardwood flooring.
The self-leveling products do not lend themselves well to plywood I know, and it certainly doesn't seem recommended to add hardwood directly over SLC. But I'm hoping that my "sandwich" approach will work. I have previously dealt with such problems by shimming and using varying layers of felt. But this hasn't always worked very well
- it's very difficult to deal with differences of more than a 16th or so. In this instance I am looking at some differences as great as
1/2". I should add that the uneveness was caused by a previous structural issue that has been fixed but that left a residual gap or two.Any thoughts gratefully accepted.
Cub.