I recently purchased a ninety year old townhouse that was converted into a 3
unit building shortly after World War II. The 3rd floor bathroom originally
had a tile floor (approx. 1" hexagonal tiles) which has sagged probably due
to settlement. I recently discovered the tile after removing vinyl flooring
which had been glued on top of the tiles.

I would very much like to install ceramic tile, probably 12" square tiles,
however removal of the old tiles and a 2 1/2 concrete subfloor is too
costly.

Figuring that most of the settlement that was going to occur probably has
done so already, I was wondering if there is any way to fill the valley
created by the sagging with a material that will level the floor
enough to install new tile over the existing tile. My guess is that the
floor's lowest point is 3/8" to 1/2" lower than its highest point.

Any suggestions would be greatly appreciated.

John