A.Tilesetter Tom Meehan, owner of Cape Cod Tile Works in Harwich, Mass., responds: Use grout. Since the shower floor, if installed properly, has a mud base (Portland cement and sand) at least 2 inches thick, there should be almost no potential for deflection. Caulk is used mostly at the joint between vertical and horizontal surfaces, where movement is more likely. One reason to limit the use of caulk is that many caulks will mildew and discolor in wet areas.

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