I want to put large format tiles in a 10 x 10' bathroom over ditra. I have a solid flooring substrate but it is sloped, losing 1 3/8" over 8 feet. I am concerned about the weight of this much SLC (and the cost). Can I reduce the thickness needed by adding sheets of ply in the low area and then use SLC over the different thicknesses of plywood?
If my math is right, and I think it is I have calculated that the slope is 1,32 % (slope is calculated in percentages; 1% means that over 1m long height difference is 1cm, sorry for using metric measurements) your slope is 1,32% which is small slope. I wouldn't use plywood or self-leveling layer. Instead you can fix this by applying different thickness of ceramic tile adhesive ("ceramic glue", sorry if translation is poor but I hope you know what I mean.