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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.
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.
If you have a 1.5” pour why not use fine aggregate cement? If your radiant heat is water tube based tack your tubes to the subfloor and pour. If it is electrical, make sure to follow the MFG recommendations. Some tapes can be bedded in the cement and this helps even out the heat. One tape I used had to be covered and the covering almost doubled the install cost. As long as your cement is not way two wet it will be fine. In my opinion a stronger floor that last the longest.
I prefer the high performance cement for these applications.
https://m.lowes.com/pd/High-Performance-Cement-by-Quikrete-Cement-Mix/50146060
