Dear James: I have recently noticed a damp spot on the ceiling beneath the shower stall. My house is only three years old. What is the cause and how can I fix it? — Nicholas D.
Dear Nicholas: For a house that is only a few years old, a faulty waterproof membrane under the shower is the mostly likely cause of the leak. You probably didn't even know that a membrane is installed underneath under the shower stall during its construction. Poor membrane installation procedures are often the culprit.
It is a common misconception that the hard ceramic tiles create the waterproof barrier and this is what blocks leaks. Although the tiles themselves will hold water, the grout between them is permeable to water. If someone takes a long shower and the tile has standing water on it for a long while, some water will get through.
A ceramic tile shower stall is made by first framing the shower stall area. A tough waterproof plastic membrane is laid on the floor and sealed around the drain opening. The membrane should extend partially up the wall behind the tile backer boards. When water gets through the tile, the membrane should catch it and direct the water into the drain.
A cement bed is placed over the membrane and sloped slightly down to the drain opening. The tile and grout are placed on top of this cement bed and up the wall to finish the shower stall.
If this does not sound too complicated and you are willing to give fixing it a try, start by removing the tile from the wall immediately above the shower floor. Use a wide putty knife with a flexible blade. Even if you find it becomes too complicated to fix yourself, you will have gotten a good start to reduce the number of hours the plumber charges.
Once you get the tile off, check the condition of the backer board under the tile. If it is damp and crumbles easily, the leaky spot in the membrane may be on the side, not underneath the cement bed. In this case, you may be able to repair it. If you cannot find the leak, it is time to call the plumber.
When the plumber removes all the old materials and starts to repair it, mention a few of these items. Cement-type backer board is best to use under tile in a bathroom. Water has very little effect, if any, on it. Even green board, designed for damp conditions, will not hold up nearly as well.
Leave a gap at the corners of the shower walls. This will leave space for the membrane to be bunched up in the corners where it is lapped partially up the walls. If you do not leave a gap for this material, it will push out the backer board near the floor, and this will be apparent. Make sure there are no nail heads protruding from the subflooring or walls.
Rout a channel in the subflooring so the drain flange is recessed and the top is flush. Without the recess, a puddle of water can form around the flange. There are weep holes in the clamping ring drain that must not get clogged with cement or the membrane. Putting small gravel over the holes should keep them open.
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