Installing a Mortar Shower Pan for a Ceramic Tile Shower

So what is a mortar shower pan?

A mortar shower pan consists of a thick but flexible membrane liner that is sandwiched between two layers of mortar in the base of the shower stall.

The first layer of mortar, known as the pre-slope layer, consists of a sloping layer of concrete that varies from about 1/4 inch thick at the adjustable height shower drain to about 1 to 1.25 inches at the shower walls, depending upon the distance from the drain to the shower walls.

Embedded in it is steel mesh to add reinforcement to the concrete. The purpose of the pre-slope is to enable water to flow towards the drain on the finished tiled shower floor. It also enables water to flow to the drain if the membrane liner was ever to spring a leak.

The thick shower pan membrane liner is then installed over the pre-slope mortar layer. A hole is cut in it at the shower drain and the sides of the liner are folded into the shower corners.

The liner is held in place with roofing nails near the top of the liner, which should sit approximately 6 inches above the shower floor. A final layer of concrete is then poured over the membrane liner to complete the mortar shower pan installation. Note that pea size stones are placed right around the perimeter of the adjustable height drain prior to pouring the final layer of mortar. This prevents the weep holes associated with the drain from becoming clogged by the mortar.

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The weep holes enable water that may get through the tile and mortar and down to the membrane liner to still drain out the drain assembly. Note that when pouring the final layer of mortar it is important to main the pre-slope pitch towards the drain.

Once the final mortar layer has been poured it is important to adjust the height of the adjustable drain assembly so that the top of it will be flushed with the tiled shower floor surface.

This needs to be done while the concrete is still uncured. Once the mortar shower pan has had a couple of days to fully cure the shower can then be tiled.

One final note. It is important when installing a mortar shower pan that the subfloor must be extremely solid with little to no deflection. If installing a shower mortar pan on a wood subfloor, there should be a layered approach with the subfloor plywood. For example, exterior grade ½ inch plywood should be installed over the base ¾ inch plywood subfloor. Make sure that both layers of plywood are screwed tightly to each other and the floor joists.

This will ensure minimal deflection so that there is no risk of the floor tiles becoming loose and the shower pan failing.