When we moved here, we tore carpet out of the 'lower level' (which is five feet off the ground at the front ) of our house. It was nasty. And the reason - we came to learn - was that the previous owners kept 17 dogs inside the house. Once the carpet was up we learned that the concrete work was so uneven it made even the most coordinated person sway and stagger like a drunken sailor when walking over it. Technically speaking it was out of flat by maybe as much as an inch. And in random ways. We were determined to put in tile because we both suffer horribly from allergies. Instead of jackhammering we had the whole thing 'floated.' The tile person came in and leveled it with some sort of special mortar before laying tile. In another part of the house with another contractor they did the same thing using Artex, I believe. That allowed them to plane or sand the surface smooth and flat. I didn't pay too much attention to the technical details because I had selected really hard and tough tile that could work with just about any material between it and the concrete.
