Q: Whenever anyone takes a shower in our bathroom, I notice water leaking onto the basement ceiling below. The leak doesn't start right away, but a few minutes into the shower. We had the ceramic tiles on the shower floor regrouted and then replaced the first couple of rows of the wall tiles, but that only helped for a few months. The shower pan is fiberglass, and one plumber told me it's part of the problem. Does that sound right?

— Ravi, Maryland

A: Richard says: Fiberglass isn't the best substrata for ceramic tile; adhesive doesn't stick to it very well and it can flex if installed incorrectly, causing the tiles or the grout (or both) to crack. Even so, the pan shouldn't leak unless it's cracked or there's a problem with the way it's connected to the drain. To find out, remove the strainer, stop up the drainpipe, and fill the pan with water. (It might help at this point to cut a hole in your basement ceiling to see if water is coming out.) If it leaks, you'll need to rip the pan out and start fresh, preferably with a new shower floor made of precast terrazzo or top-of-the-line acrylic, or of tile set in a thick bed of mortar applied on-site over a waterproof pan.

If the pan isn't leaking, and you're sure water isn't getting around the shower door or curtain, perhaps the drain itself is the culprit. Remove the plug and pour water directly down the drain through a funnel while someone stationed in the basement with a flashlight looks for drips. No dice? The valve or the supply lines leading to the showerhead could be dripping into the wall cavity. Turn on the shower and catch all the water in a 5-gallon bucket. If a leak appears, you'll have to go through the other side of the wall to make the necessary repairs.

If all these tests fail, water may be getting behind the escutcheon plate, the metal piece that surrounds the valve handle. A plumbing supply store may have a gasket to fit it. If not, caulk the escutcheon's perimeter with a mildew-resistant, acrylic-latex sealant. Finally, it's also possible water is penetrating grout cracks between the wall tiles, which means you should regrout where necessary or retile the entire stall.
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