Mortar Shower Pan Installation Stack Up

Lack of Pre-Slope Mortar Layer is Often the Problem with a Failed Mortar Shower Pan

Frequently I get people who contact me explaining their shower has a leak, and that the mortar shower pan was to blame.

Often they tell me horror stories on how the mortar shower pan was installed.

One of the most common problems I hear is that the mortar shower pan installer did not put a pre-slope in. This is a huge mistake in the event the shower pan membrane liner does spring a leak or becomes compromised in some way.

The pre-slope mortar layer is the last defense in a failed shower pan for ensuring that water drains to the shower drain. Without it, water will end up sitting underneath the tiled shower floor and slowly degrade both the shower pan and the subflooring below it. And if there is a finished room underneath the shower, then water damage to the lower level is inevitable.

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Use the Mortar Shower Pan Stack Up Shown Below When Installing a Shower Pan

By following the mortar shower pan stack up in this drawing you can be assured of a leak free shower pan. I have never experienced a failed shower pan from installing one this way.

Note that it is important to place pea stone around the adjustable shower drain prior to pouring the mortar into the shower pan area. The pea stones prevent the small holes in the adjustable drain assembly from becoming clogged with the mortar when it is poured.

This mortar shower pan installation stack up works for both a shower pan being installed on a wood subfloor or concrete slab. Note that on a wood subfloor, the subfloor should consist of the original ¾ inch tongue and grooved sheathing followed by at least ¼ inch thick plywood on top, and preferably ½ inch thick. This will help to ensure negligible deflection in the subfloor.