How thick should the Mortar Bed for a Shower Pan Floor in a Shower?


When you are pouring you mortar for on your shower pan how thick do you want it before laying of tile


ANSWER - First of all, the way you construct a shower pan is to first apply a pre-sloped mortar bed to establish a slope to the drain of 1/4" per foot.  You can float over a concrete substrate or nail on metal lath over a wood subfloor.  Then you have to waterproof the pre-sloped mortar bed with either a liquid applied membrane or a sheet membrane. Then you float a dry-packed mortar bed over the pre-sloped membrane to a thickness of at least 1.5" thick.  The mortar bed should have wire reinforcement fabric suspended within the mortar bed if it is a shower pan area larger than 65 square feet.  Otherwise you can leave off the wire reinforcement. Per ANSI A108.1A-2017.  So after installing the tile the slope to drain should be a minimum of 1/4" per foot, but should not exceed 1/2" per foot per the IAMPO plumbing code IAPMO PS 10612015e1.

7 thoughts on “How thick should the Mortar Bed for a Shower Pan Floor in a Shower?

    • Donato Pompo says:

      It is normal to have a shower curb/dam. It is going to be 4″ tall or so from the bathroom floor. Although curbless showers that were originally meant for handicap showers has become more popular and more in demand.

        • Donato Pompo says:

          ADA (Americans with Disabilities Act) requires a curbless shower so that it can be accessed with a wheel chair.

          So depending on whether the shower is constructed on a concrete substrate on-grade or over a subfloor with floor joists, and the configuration of the shower assembly the thickness of the mortar bed can vary. Non-bonded reinforced mortar beds are recommended at a uniform minimum of 1/25″ and bonded mortar beds can vary from a feather edge to multiple inches thick. Regardless of the thickness, it has to be mixed and installed appropriately.

  1. M says:

    How thick should mortar bed be at the drain if the mortar bed is sloping down to drain over flat substrate? can it be smaller than 1.5″ at the drain?

    • Donato Pompo says:

      If you are installing an unbonded wire reinforced mortar bed per TCNA TR40-23, the mortar bed should be a uniform 1″ to 1.75″ thick, but it should be installed over a pre-sloped primary waterproof membrane. That means that the wood or mortar base under the waterproof membrane has to be sloped to the drain at 1/4″ per foot. The weep holes around the drain where the membrane clamps, must be protected with a weep protector that can be a plastic weep hole protector or pea gravel. We always also recommend to install a liquid applied waterproof membrane over the mortar bed to keep water out and to bond the tile to the membrane. You then need to fill all of the transition joints with an ASTM C920 sealant caulking such as a structural silicone or a polyurethane sealant.

      If you have a concrete base you can install a bonded mortar bed to the concrete and then the mortar bed doesn’t have to be a uniform thickness. You can slope the mortar bed from thick to thin, depending on the type of mortar you use. Using a polymer modified mortar allows you to slope from thick to thin. You would then waterproof the mortar bed. You can use a standard two part drain per TCNA B421C-23 or an integrated bonding flange drain per TCNA B422C-23.

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