Replacement options for < 1.5 inch pour?
Details: Bathroom remodel (new tub, tile wall/floor, toilet, vanity). Old tile floor came up with finger pressure, found that the gypsum concrete underneath was unstable, coming off in large loose pieces, and mildewed. Removed all gypsum concrete in the small bathroom. OSB is in great shape. Supplemental goal to install underfloor radiant heating.
Best Answer
We generally don't recommend self leveling alternatives on a substrate other than concrete, vibrations over time can affect their stability. Best option is shims and plywood.
That being said, you're asking for a self leveling option. Your best bet would self leveling concrete, you'll need to pay attention to the substrate requirements, it says it accepts certain wood based substrates, however compare their requirements to your situation.
like: http://www.lowes.com/pd/MAPEI-Gray-and-Silver-Indoor-Floor-Patch-and-Leveler/1180155
Also, most of these 'concretes' are safe for electrical radiant flooring installations.