We have a slate tile floor and need to replace part of it. The previous owner of the home did not seal an exterior door, so the sub-floor under the tile around the door is rotted and the tile is cracking. The grout lines are staggered and not straight, so we'll have to cut some of the tiles to make a straight line. What is the best tool to use to cut a (reasonably) straight line in the tile? Thanks for your help!