I was thinking of using a scratchcoat to level out the floor over the OSB and then apply the ditra over top? Would this approach work? I thought about using the Mapei Novaplan2 SLC compound, but I'm reluctant after hearing stories about this product.
Scratch coat is not for leveling. What have you heard about that product? There is a story with every DIY SLC project. Those type of products can all be tricky if you don't follow directions to a T. There are many other brands too.
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.