My house is 1 story, but I have a basement so all the floors on the main level are "upstairs" and have a wooden subfloor. I ripped out the vanity in a bathroom I'm working on and starting taking out the tile. I had a bit of trouble because the vanity had to be lifted almost 2" to come out which I thought was odd. It looks like there is some type of poured in "concrete" like material above the wooden subfloor and the tile. Any idea what this is? Can I just pour in more where the vanity was to level it out?
This floor has been floated, a very common and traditional method for preparing surfaces for tile. To "float" is to apply a cement and sand mix similar to concrete but without rocks, gravel or coarse sand. A 2" thick float is not uncommon at all.
It is often applied using a "dry pack" method wherein only enough water is mixed to ensure proper set but wet enough to pack, shape, feather, and blend.
Do not use pre-mixed bagged concrete mix. If you do not want to mix your own, use pre-bagged mortar mix and "dry pack" the area. I guess you could then use a thin layer of floor leveling compound to flatten, smooth, and blend the damaged areas and seams.
thats drypack. its an older way to prep a floor to allow for tile installation. it was used to allow for the floor to breathe, so any moisture that got past the tile mortar didn't get trapped between the tile and the base (as it would if you just used concrete). nobody does it anymore because the last two decades have seen the use of polymeric modifiers to almost all grouts and mortars. it use to be standard practice for good to high quality tile work. just fill the hole with sakrete or some other such concrete pre-mix in a bag (3/8 stone or bigger, 32mpa or higher - almost all bagged concrete meets this requirement)