I am installing a floating wood floor. The living room is an addition to the house & there is a long 7 - 8' doorway where the subfloorings is about 1/2" difference in height. I was told by a contractor not to use a self-leveling compound, but to use a clay fill and blend it into the lower floor. I can't find anything on the internet about a clay fill. Anyone have any ideas? Any help is appreciated

Thanks,
L