What's the deal with door thresholds. I have conflicting advice and need help... I had my kitchen tiled and stopped the tiller because he tiled onto the metal threshold to the exit door. (I forgot to mention I would be changing out my kitchen door.) The tiler has the edge of the tile in line with the door frame but he had to tile onto the metal threshold to do it. NOW heres my ? Things expand.... should the tiler have removed the old metal threshold to tile under it and/or leave a space to caulk to allow for expansion?