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.

19 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.

  2. Ellis Joiner says:

    We had our shower tile redone and the installer is telling me with the floor being concrete it does not need to be sealed .

    • Donato Pompo says:

      All shower pan floors need to be waterproofed if that is what you mean by being sealed. This is a requirement by the international plumbing code and per industry standards.

      If you are asking if the concrete slab has to be sealed with a sealer prior to waterproofing, then it that case the answer is no. It does have to be properly prepared for the intended application.

  3. William Fisher says:

    I am installing a pan with preslope, liner then mortar bed and finally tile. My floor turns out is not level and slopes away from the drain. I need to have a thicker preslope at the curb and really need to feather it out as you get to the drain. What type of cement would you use for the preslope. It will be real thin at the drain. I need to make up about an inch of sub floor slope. Would thin-set work? Thanks for your input. Bill

    • Donato Pompo says:

      Assuming that you have a structurally sound substrate to bond to, there polymer modified mortars known as patching mortars or fortified mortar beds that you can apply from several inches thick down to a feather edge. They normally require exterior grade plywood to go over or a cementitious base material.

      You then need to apply your waterproof liner over that and tie it into the two part drain for clamping, and to transition it up the wall at least 12 inches. You then can float your mortar bed on top of that in a uniform thickness. We also apply a liquid applied waterproof/crack isolation membrane on top of the mortar bed to keep the water out of the mortar so most of the water evacuates into the surface drain. This gives added crack isolation protection as well as a good secondary waterproof membrane.

      The ANSI A118.4 and A118.15 clearly state never use thinset to adjust a subfloor. It is not designed for that.

  4. Kristen Sullivan says:

    Hello! I currently have an issue with my contractor. My bathroom was visibly remodeled poorly. There is a concrete subfloor (which can’t be drilled into because it’s in a building with an HOA). They were supposed to install a curbless shower with only a glass wall to separate the shower area from the rest of the bathroom. They stated they couldn’t install a linear drain. The entire room (other than the ceiling) was to be tiled. They were supposed to waterproof the ENTIRE room – including up the walls. I told them I was happy to pay for them over doing it even though they felt it was overkill.

    The first issue – they didn’t tile the walls of the bathroom (just that of the shower). When they went to complete this error, it became really apparent that they hadn’t leveled the floor. They also installed a shower curb stating it’s per code. – and the shower is two feet smaller in depth than it was supposed to be. The floor of the shower is DRASTICALLY sloped with a center drain and is so sloped it’s awkward to stand in. At the far corner from the shower there is almost a 2 inch gap between the floor tile and the bottom tile (so the grout line from the bottom tile gets larger as it goes away from the shower.

    I previously had a slight lip – so not technically curbless but pretty close. I could have walked in with a broken leg or gotten a wheelchair in there if needed.

    They want to fix the size of the shower, keep the curb as they say the curbless is not allowed per code (IBC) and not replace the wall tile as they will just level the floor so it matches the existing tile line.

    Any ideas where I can find that a curbless shower can be installed without impacting the current subfloor (concrete)…it also seems like I could install a linear drain to resolve some of this issue…but they say no because the drain location can’t be moved (I have since found a video of a linear drain that can retrofit with a center drain but they are all about doing as little work as possible to fix their mistakes).

    They are now claiming that per code they are not allowed to install a curbless shower. Clearly these are allowed – I’ve had them before in a few homes and they exist regularly. Am I incorrect in thinking this can be done? And are you aware of any code that allows it? (I think it’s literally required for ADA situations-I just don’t have a code to show them).

    • Donato Pompo says:

      Sounds like there are a lot of things done improperly per your expectations as well as per industry standards and the building code.

      There are more limitations at installing a curbless shower over a concrete slab, but it can be done depending on the other conditions in the bathroom where there maybe limitations or tradeoffs. Per ADA requirements curbless showers are required for certain circumstances.

      The slope of she shower pan is recommended to be 1/4″ per foot and not more than 1/2″ per foot per IAPMO code.

      Although it isn’t always practical, you should hire an architect and tile consultant to make sure the installers perform the work correctly as often they are not familiar with the standards.

      • Kristen says:

        thanks for confirming what I think I already know. Any clue how I find someone reputable (Steamboat Springs, CO)? It seems like the town has grown so quickly that it’s VERY difficult to find truly experienced, trained people. People seem to get whomever is willing to do the work (hence my issues…).
        THANK YOU for your responses!!

        • Donato Pompo says:

          There isn’t many qualified experts in the tile and stone world who can provide a valid and informative opinion on various types of tile installation deficiencies. Plus often it is not affordable or practical to hire a qualified expert, and it is better to spend the money repairing or replacing the installation than to prove fault.

          Although if you don’t understand what caused the problem you can’t determine the appropriate remediation required to correct the problem so it doesn’t reoccur.

          Often the focus is on the symptom of the problem rather than what caused the problem because it is easier and less costly. If you don’t fix the problem then the problem doesn’t go away.

          Ceramic Tile And Stone Consultants, Inc. does provide nationwide services and has inspectors located throughout the USA near most major markets. Visit for more information.

  5. steven welborn says:

    Hello. I was hoping to be able to build a curbless shower over a plywood subfloor with linear drain along backwall (58″) and doing a mud bed (over tar paper/lath) sloped up (flat single plane) to shower entrance (32″ or 34″) transitioning into main bathroom area. I plan to recess the shower subfloor by inserting plywood between the joists so subfloor is flush with top of joists. Main bathroom plywood subfloor (two layers) is 1 1/4″ on top of joists. I was planning on doing a traditional mud pan and hoping to keep from having to raise the main bathroom floor anymore than it is for level transition into adjacent room. Do I understand correctly that the minimal thickness of mud pan where it meets the linear drain would need to be 1.25″ thick (then sloping up another 3/4″ to shower entrance) ? Also, sounds like I may be missing a crucial stage here…over a plywood subfloor, do I need to first float a morter sloped bed, then an ADDITIONAL mud bed (even thickness over that) ? If thats the case I may need to scrap the curbless idea and go with a curb, and a slightly higher shower floor, if I want to maintain the main bathroom floor level as it is.

    • Donato Pompo says:

      The TCNA standards do not show a curbless shower installation over a wood subfloor, although it is done. ANSI A108.01 does show a 3/4″ mortar bed installation over metal lath for residential applications. TCNA F145 does show a mortar bed over metal lath application that was with a waterproof membrane can be suitable for water exposure. There are curbless applications in the TCNA Handbook with an area drain in the center of the shower that gives you more flexibility.

      There are kits you can buy that provides brackets for recessing your subfloor between floor joists. In theory, you could install blocking around the perimeter walls and then hop mop over the recessed wood subfloor and blocking. Since you won’t be using a two part drain with weep holes you don’t need to pre-slope the floor as the secondary waterproof membrane should keep water from getting there, but the hot mop provides protection if the secondary membrane gets breached. Then staple or screw down galvanized or stainless steel metal lath. If using screws pre-drill holes and fill with ASTM C920 sealant as you screw down the metal lath. Then float a sloped mortar bed over it so the bonding flange on the trench drain is level with the surface of the mortar bed. Ideally you want to achieve a 1/4″ per foot slope to drain. Then use a liquid applied waterproof membrane like Laticrete Hydro Ban or Custom Red Gard or Mapei Aqua Defense over the mortar bed, over the bonding flange, and up the shower walls. After the membrane has cured for 24 hours or more, flood test the shower pan for at least 24 hours. If the shower pan passes the flood test, then bond your tile directly to the waterproof membrane with a polymer modified thinset mortar recommended by the waterproof membrane manufacturer.

      Install movement joints at all of the transitions of the trench drain and at the transitions of floors to walls, at vertical joints between two adjacent walls, and at the shower pan floor to bathroom floor transition filling them with an ASTM C920 sealant (100% silicone or polyurethane) over closed cell foam backer rod or bond breaker tape.

      The important part is that the wood framed floor is sturdy and will not deflect more than L/360 for ceramic tile or more than L/720 for natural stone. If necessary add additional bracing to the floor joists.

      • steven welborn says:

        Thanks for your response and expertise! Pleased to hear that’s it’s do-able project. Hot mopping and installing movement joints are new to me, but sound key in the process.
        Would leaving clean gaps filled with foam backer rod and correct sealant suffice for movent joints, or are the pre fab metal joints necessary?
        If gaps/rod/sealant are acceptable, do they need to be minimum1/4″ or would 1/8″ work in keeping suit with the rest of the tile grout?
        Using hexagonal mosaic natural stone tile for the floor would create a tricky situation with the movement joints especially where shower floor transitions into bathroom if tiling entire floor with those. I’d either need to cut a straight line across the mosaic for an ideal movement joint, or do a small zig zag less ideal joint.
        Fortunately I’ll be able to reinforce joists and under structure in a way to allow recessing more than I thought, as much as 2 or 2 1/4″ below existing bathroom subfloor if needed, possibly without having to insert planks between joists and placing the full sheet on top of joists.

        • Donato Pompo says:

          The prefabricated movement joint profiles are faux expansion joints. They have metal or hard plastic L angles that are bonded to the underlying substrate. So they actually constrain the tile. You could put a sealant joint between the metal profile and the tile , but it isn’t a true movement joint. Best to fill movement joint with an ASTM C920 sealant over foam backer rod or bond breaker tape. that will perform much better and last a long time.

          The standards recommend a minimum 1/4″ wide movement joint, but if you have more frequent movement joints or if you perform the ASTM calculations often a minimum 1/8″ wide movement joint will suffice as long as the sealant is at least 1/4″ thick.

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