I'm trying to figure out how concerned to be. Most of the basement has slate tile, but I tore out a kitchen, and discovered this crack running from the nearest wall, to the sink drain, and on across the floor in the direction of the sewage pump, and near a support post. I pulled a tile up closer to the post and the crack seems to be turning away from it, so I don't think it's related to the post. Do I need to pull up the rest of the tile to fix it? Should I avoid tiling over it? Whoever built the kitchen had filled the crack with some sort of rubber cement. There doesn't seem to be any evidence of water from it.