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Pre-Sloping Shower Pan

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  • Pre-Sloping Shower Pan

    Hey experts!

    I've got myself into a bit of a pickle. Shortly after moving into my house in August, I found a loose tile in the tile shower. I pulled it off, thinking I'd just re-attach it and all would be well.

    All wasn't well.

    One thing led to another and now the shower is pretty much a pile of rubble.

    I'm now cutting out some of the framing and pulling out the old pvc shower pan. I'm pretty sure I found the cause of the damage. The pan didn't extend up over the doorway so water leaked down there and then wicked up the drywall, dissolving it and rotting the wood.

    So now I'm building a new one. I've been doing my research and realize that I should pre-slope the floor before putting down the new liner.

    This describes it.

    I really haven't found anything to really detail how I'm supposed to get the slope done though. It's a rectangular shower but the drain isn't in the middle. It's about a foot from the shower head. Do I just spread out the concrete and then just sort of eye-ball a bowl shape? That doesn't sound very accurate and I don't want to end up with a surface that I can't lay tile on due to the shape.

    Any suggestions or tips and tricks?

  • #2
    pre-sloped shower floor.

    Hi. Here's how I do it. 1) establish final overall depth around perimeter with a line or marks (laser sitting on drain location is ideal tool). Subtract tile thickness and about 75% of mortar depth; that's your preslope line. 2) You don't want a 'bowl'. Use series (2?) of different length straight edges, one end on subfloor at drain location, other extending to your lower line (place mortar around perimeter to this line, then fill in between) on wall. Better a low preslope than a high one. Remember, 1/4" min. slope/foot. 3) Lay membrane, install drain. Keep the folded membrane corners from getting fat above the bed or you'll have trouble with the corner tiles. 4) Install bed #2 to line below tile thickness. Again, low is Much better than high. 5) Use a tile mortar that can be laid thick if necessary and set the tiles with a wooden & brass level, checking slope as you go. Good luck.


    • #3
      Thanks bclint!

      I think that's the key to the puzzle I'd been missing. Marking out the various depths first before putting in any concrete.

      When you say I don't want a bowl though... I'm not sure what you mean about the multiple straight edges. Am I basically making a sort of star shape? A bunch of angled triangles coming together at the drain?

      I'm assuming this is why you often see the little mosaic tiles used for shower floors. They must be more forgiving when laying them at the angles where these triangles meet one another.

      Does it make sense to slope the long end of the floor (from drain to far wall) as one flat slope and then treat the area around the drain as a square?


      • #4
        A bunch of triangles seamed together is not a bad way to think of it, but you do want to smooth out the surface concentrically around the drain, like the inside of a funnel. My point about the bowl is not to deviate much from the straight (but sloped) line that exists between the drain and the wall level at any point. A slight raise at the wall, a slight dip approaching the drain. Not bowl; 'flat funnel' perhaps. You should keep your slope at the minimum so you're not having to make much up on the shorter side from drain to shower wall. A mortar you can lay up to 3/8" thick, if your tile is 1/4", say, will enable a smooth transition around and allow 6x6's at least. Use your levels to nudge them into the adhesive (which is your 3rd layer of mortar).


        • #5
          Too much pitch will also make the shower floor uncomfortable to stand on, would it not?
          "It's a table saw, do you know where your fingers are?" Bob D. 2006


          1/20/2017 - The Beginning of a new Error


          • #6
            Yeah, too much slope would definitely be uncomfortable. It seems that 1/4" rise per foot is about standard. I'm assuming that with so little slope, you shouldn't even notice when standing in it. I'm sure it will feel flat, as does pretty much any shower I've ever stood in.

            I get it with the funnel shape. Good stuff.

            What about my idea of using a constant slope (1/4" per foot) for the long side until I come near the drain and then treating the area around the drain as a square?

            I've got a few days off next week so I'm going to dig into this in earnest. Hopefully I'll have it all framed and ready to start mixing concrete.

            Thanks again for the advice, guys!


            • #7
              For reference, here's some pics of what I'm working with. This is as far as I've got so far, and looks phenomenally better than it did a week ago, before I got the Ridgid vac. The first pic shows the bathtub beside it, still filled with pieces I've pulled out of the shower. I haven't figured out what to do with them yet but the best idea seems to be to get an outdoor fireplace.

              The second pic shows the shower. The old liner is still in there and needs to be ripped out. That will be next. Then, instead of replacing the wooden bits that are holding the liner in place, I'm going to use plywood to build a box into which to put the presloped floor and then go from there. The liner will go inside the box rather than having wood going inside the liner. That seems stupid to me and all those wood bits have started to rot at the bottom, just as you'd expect them to. I figure wood goes on the outside, cement board goes on the inside.


              • #8
                Forget what I said about a level mud line around the bed. Your drain is too close to the wall. Work back from the drain adding your 1/4"/ft as you go. You could get steeper between the wet wall and the drain, say 1/2", it's so close. I wouldn't aim for a flat square around the drain; standing water s*cks. Keep the flat funnel in mind as you trowel. So now you have a rising line on the back wall and the sill side. Run a level line above that high enough to have a reasonable smallest piece of tile. Set your floor, grout your floor, protect (that's just my preference); then set the second row of tiles on the wall (the whole ones) and up from there for as many as you care to do.
                After that section has set, sitting on a tacked-on straightedge; remove the straightedge and fill the 'baseboard' with pieces. Keep the tile and the backerboard 1/8"+ off the floor so you can silicone the seam. Use kneepads and stretch before starting...


                • #9
                  If you tack a strip around the perimeter for your pre-slope and use the different length floats (very handy for someone like me who only does a bed like this once in a while) your bed smooths into place. Run your mesh close to the drain location. Remember your low point at the drain is the box (0), + the thickness of anything on the plywood + the liner + the tile & adhesive. I then set the top of the finish drain flange 1/8" below that point. After the liner is down a wider piece of straightedge tacked above the liner so the bottom edge is the guide will serve as a form for the mud around the perimeter. You take it from there.


                  • #10
                    Thanks again, bclint! I understand your first post but am not too clear on the second.

                    I have no idea what floats are. I'll do some research on that though. I think the mesh you're talking about is the steel mesh stuff that you put into concrete but I hadn't planned on using any. There wasn't any in originally and I figure it will just rust within the concrete like some of tha nails that were exposed to water did. Is that not the case?

                    Also... you can't really tell from the pic, but the part with the gray tiles there is above the level of the shower, and is where the top of the dam was. I think that was the main cause of the damage. The liner didn't come up over the dam, and the top of the dam is level with the flooring there. It's a raised platform into which the bathtub is set. The water just seeped down between the dam and the drywall, outside the liner.

                    I think if I make the dam 1 2x4 higher than that step, that will allow me to put the liner over it but that means it will be 5 2x4's high. Is there some limit to this sort of thing? Will elderly people not be able to step out of the shower in the future?

                    This thing makes me a little madder each time I work on it. I've just finished stripping out the liner and found that the drain is permanently attached. From what I've read, there's no need to do this since the concrete will hold it firmly in place. That would be ok if I could still use it, but 2 of the 3 bolts holding the top piece on just broke off when I went to turn them.

                    Finally, whoever last renovated this shower just put new tile over the old tile and then filled in the drain with grout to bring it up to the level of the new tile. I can't believe any water at all was still going down this thing! It was nearly filled right in with grout! I've chipped all of it off that I could see and sucked out the bits with the shop vac. Hopefully there's none now down the drain that's going to cause me a problem.
                    Last edited by Wild Weasel; 01-02-2007, 01:28 PM.


                    • #11
                      Wild Weasel'

                      A piece of advice: take or leave it. Look at the qualifications of the people you take advice from.

                      I will give you one piece of advice myself, take or leave it: Don't use a bathtub you intend to keep as a debris pit.
                      the dog


                      • #12
                        Thanks. I put a bath mat down in the tub before I started to protect the bottom and have been pretty careful when placing pieces into it, but yesterday I did start taking the bigger pieces out as a start to clearing it up. Now that most of the demolition is finished, I have no need to leave pieces in the bathroom anymore.

                        Things are starting to move along. The next scary part will be cutting off the old drain and hoping I can still reach the pipe to attach the new one.


                        • #13
                          Hi. If you're concerned about the hgt. of the step (ok in my opinion) add a small step on the inside! I always use galv. mesh; helps prevent stress fractures. Force the mortar into the tacked on mesh. The job you do with liner and above will keep any rust down, yes? Floats are nothing more than lengths of straight material used to spread and finish the mortar. You should be reading more how-to's. They're out there. Drain is attached? To a lead bend? PVC? Either one can be cut out. Or do you mean just the flange?


                          • #14
                            Yeah, I need to remove just the flange since 2 of the 3 bolts holding the top piece on just broke off when I turned them. Otherwise it would have been much easier since the new drain I bought is exactly the same as the one that's there! Apparently they haven't changed a bit in the past 21 years or so since this house was built.

                            What I'm wondering though, is whether I can cut out part of the shower floor and move the drain over toward the middle of the shower. Is there some specific bends or a specific amount of vertical drop that's necessary for it all to work properly? As I can see, it drops staight down at least 6" or so from the drain and then I don't know what it does. I assume there's a trap there and then it probably doesn't matter. If instead of coming straight up 6" though, it ran on a 45 degree angle toward the middle of the shower or something, would that cause me problems?

                            plumbdog: You'll be proud of me. The bathtub is now completely empty of debris, and will stay that way. Thanks bro!


                            • #15
                              Re: Pre-Sloping Shower Pan

                              Wild W. I have been away for a bit and just now see your last post. How's it going?