The following five-part series gives a basic overview of building a shower floor for tile. If you would like a complete step-by-step of the entire process with all the little idiosyncrasies and details  I now have manuals describing the complete process for you from bare wall studs all the way up to a completely waterproof shower substrate for your tile.

If you are tiling your walls and floor you can find that one here: Waterproof shower floor and wall manual.

If you have a tub or pre-formed shower base and are only tiling the walls you can find that one here: Waterproof shower walls manual.

Curb and Pre-slope

Image of a shower diagram

Properly built shower

There are a couple of options to create a shower floor for tile using deck mud. The first is a single-layer shower floor which can then be coated with RedGard or a similar product or covered with kerdi to waterproof it. The other is a normal shower floor with a liner which will have two layers – a preslope, the liner, then the top slope which is then tiled. This series of posts will describe the latter.

Before we start I should note that unless you are using the kerdi waterproofing method or utilizing a liquid membrane as your floor liner you should not have the backerboard installed in the bottom part of the shower. Your waterproof membrane for a shower floor will be installed behind your backerboard. The curb and pre-slope need to be completed before installing the lower wall substrate.

Creating the curb for a wooden floor

The first thing you must do is create the outside curb of your shower. You need to create the “box” which will become the inside of your shower floor. Depending upon whether your shower will be created on a wood or  concrete floor will dictate what material you use for your curb.

If you have a wooden floor you want to use regular dimensional lumber. The 2 x 4’s they carry at Home Depot – those. That is the easiest and most readily available material. Ideally you want to use kiln-dried lumber. That is lumber that is, well, dried in a kiln. By removing moisture in this manner the moisture content of KD lumber is normally between six and eight percent compared to regular dimensional lumber at close to 15%.  Why does that matter? Well moisture and wood don’t mix. As it dries wood has a tendency to warp and twist. The less moisture initially in the wood the better.  KD lumber is best and regular air-dried dimensional lumber is also acceptable. NEVER use pressure treated lumber – ever.

I usually use  three or more stacked 2 x 4’s to create my curb depending on the size of the shower. Simply screw the first one to the floor (with correct non-corrosive screws), stack the next one on top and screw it down, and so on until the desired height is reached. That easy.

Creating the curb for a concrete floor

Image of a brick curb

Using Bricks for a shower cub

For a concrete floor you want to use bricks. Yeah, bricks. Just stack ’em. I use gray concrete bricks (no holes) and stack them two or three high for my curbs. You can use just regular thinset to adhere them to the floor and to each other. Just stack them in the shape you want.

You do not want to use wood for your curb on concrete. Wood will actually absorb moisture from your concrete and start to swell.

Creating the pre-slope

This is one of the steps most often skipped by a lot of people – amateurs as well as professionals. It is imperative! You need it – it’s that simple. Without a pre-slope your waterproof liner will lay flat on the floor. This does not give water anywhere to go. It will sit there, stagnate, mold, . . . you get the idea. With a proper pre-slope any water will drain to the weep holes in the drain and go where it needs to – away.

Lathe for wooden floor

Lathe installation for wood floor

You need to first make sure your shower floor will stay where you put it. On wood you can use regular metal lathe.

You need to place what is called a ‘cleavage’ membrane beneath your lathe. This is just a sheet of plastic or tar paper stapled to your wood floor first with the lathe placed over it. The membrane does not make anything waterproof! If someone tells you that hit ’em in the head with a bat. It is necessary to prevent the wooden floor from sucking the moisture out of the pre-slope prematurely causing it to cure too fast (or not fully) and significantly weakening it.

When your membrane is down staple the lathe over the top of that. Just cut it to the shape of your shower floor and lay it flat on the floor and staple or nail it down. This gives your mud bed something to grab onto. In the above photo I have used plastic as my membrane and only have a partial piece of lathe in – make sure you cover the entire area below your pre-slope.

Image of a properly prepared pre-slope

A properly prepared pre-slope

For a concrete floor you need to mix up some regular thinset except you need to mix it “loose”. That just means you need to add a bit more water than the instructions call for to make it thinner. Cover your shower floor area with this before you start installing your deck mud. The deck mud itself does not “stick” to anything, you need to supply something that will adhere it to your substrate.

Oh crap – Math???

To make the installation easier you’ll want to mark your height lines on your wall studs. To figure out how high it needs to be off the floor you need to figure out your slope. This involves a bit of math – don’t panic! It’s easy. Figure out which corner is farthest from the center of your drain. Your slope needs to go up in height 1/4″ for every foot. If your furthest corner is three feet from your drain center your slope needs to rise 3/4″. Easy enough so far, right?

Your finished floor (after your liner and top mud bed are installed) needs to be 1″ to 1 1/4″ thick at the drain. So, if we make the pre-slope  3/4″ thick at the drain it needs to be a total of 1 1/2 inch thick at all your walls. So mark a line 1 1/2″ from the floor all the way around the wall studs. This will be the height of your pre-slope at the walls. I try to make my pre-slope the correct thickness at the drain so it will be 1 1/2″ at the walls. This way you do not need to draw lines, just level your perimeter with the top of the 2 x 4 studs along the bottom of the wall. Depending on the size of the shower it doesn’t always work, but it saves time if you can work it out that way.

If your shower is not a square, and they rarely are, you still need to have the same thickness at the walls all the way around the perimeter. This means that you will have a steeper slope on the walls closer to the drain. This is normal. If you don’t do it this way you will have uneven tile cuts at the bottom of your wall. By doing it this way you will ensure a level line and, in turn, a level floor around your perimeter.

The height of your pre-slope at the drain can vary. It  needs to be level with the top of the bottom flange of your drain. Regular drains have two flanges which bolt to each other. The pre-slope needs to be at least level or a touch higher than the bottom flange. Your liner then goes between the top and bottom flange to utilize the weep holes in the drain. This allows any water atop the liner to drain. The pre-slope supports the liner so it needs to be level or above every point of the lower flange. Does that make sense?

This is why planning is so important. Your drain needs to be high (or low) enough and your curb needs to be higher than your shower floor – naturally. So figure all this out before you build anything.

Playing with mud

Now we need to mix up a batch of deck mud. Check out that link, I’ll wait . . .

Okay, once your mud is mixed up you want to start packing it in there. If you are going over concrete and have your thinset slurry down, cover the entire bottom of the shower floor first to ensure the entire base will stick. If you have a large shower only spread as much thinset as you can reach over at a time. Start at the walls and pack your mud down really well – beat the hell out of it. Seriously, beat it like the last DMV employee you spoke with. You want to eliminate any voids and create as dense a bed as possible. Don’t worry, it won’t hit back.

Pack it down around the perimeter to just above your line. When you get that done get yourself a 2 x 4 about 18 – 24 inches long. Lay that on top of your mud bed against your wall and tap the 2 x 4 down with your hammer until it is even with your line. This ensures a level, even line all the way around your perimeter. Perfect! Now don’t touch the edges.

Image of properly prepared deck mud

Properly prepared deck mud

Continue to pack mud into your shower base all the way from the perimeter down to the drain. You should have a straight line from the perimeter to the drain without any dips or humps. This will allow water to drain correctly without pooling anywhere. While this particular layer of your shower floor does not have to be exact, you do need to make certain it is fairly flat in regards to the line from the perimeter to the drain.

Image of a consistent pre-slope

Ensure a consistent slope

That’s it. When you get it all packed in there it should have a shape similar to a very, very shallow bowl. Now leave it alone. Really, leave it alone. The next day it will be ready to install your liner and all that fun stuff. Don’t play with it until then.

In my next post I will show you how to install your waterproof liner. Until then leave your pre-slope alone. It’s fine. Quit trying to perfect it. We’ll do that tomorrow. Get away from it. Really. Stop staring at it . . .

Read this next if I haven’t already bored you to death: How to create a shower floor Part 2

{ 713 comments… add one }

Leave a Comment

  • Isaac K

    Hello,
    I’m hoping you can help me out here. I installed my shower pan about a week ago. Today I went to hang the backer board and noticed that I’m getting movement around the edges of the shower pan and I can see the liner move some as well. The shower pan and pre slope are all on a concrete floor so I know there’s no movement there. And the prestige didn’t have any movement in it either. Do you have any idea as to what would be causing this and how I should continue?

    Reply
    • Roger

      Hi Isaac,

      What do you mean by ‘movement’? Is there open space behind the liner (liner not fully pressed against the footer)?

      Reply
      • Isaac K

        When I would put pressure on the outside edges of the pan it would move and I could see the liner flexing. So I’m assuming thats what it was. I had the liner pulled to tight and there was a gap around all of the edges at the footer. I went ahead and tore it out yesterday and reinstalled it making sure that the new liner is squared into the footers.

        Reply
  • Bill Hewitt

    Great advice! Just put down the preslope and it worked perfectly. Thanks!

    Reply
  • Rebecca

    Oh no, why is it a bad idea to use pressure treated 2x4s for the curb on a concrete slab? We just did that (we thought pressure treated would be water resistant against the slab) last night and covered the 2x4s with hardibacker and we were hoping to pour the slope tonight. What would happen if we don’t tear it out and put in bricks?

    Reply
    • Rebecca

      If the pressure treated wood was already old and pretty dry, would it probably be okay?

      Reply
      • Roger

        Unfortunately no.

        Reply
    • Roger

      Hi Rebecca,

      Pressure treated wood is created to remain in wet or humid areas (like concrete) without warping because it has chemicals infused into it to balance out the moisture infusion (if that makes sense). If you use it for a shower curb the chemicals in the wood dissipate, since one side of it is getting constant moisture (the side against the concrete) and the other three are not. When that happens it can warp and twist. When the substrate beneath your tile warps and twists it cracks grout and tile. You really should replace it.

      Reply
      • Rebecca

        Thank you for your help!

        Reply
  • Christopher James

    Should my bottom flange be level with sub floor before I do the preslope?

    Reply
    • Roger

      Hi Christopher,

      Ideally it should be about 1/2″ above it to compensate for the preslope thickness.

      Reply
  • Cole

    Hi Roger,

    I have my bottom flange glued to my drain pipe and it comes out at the right height. There is a little back and forth play and I was wondering if I should use adhesive to hold it in place or just pack the preslope around it to hold it in place? I guess that begs the question should I fill the gap in the subfloor and lower drain with something so mud does not fall through?

    Reply
    • Roger

      Hi Cole,

      Is your flange floating in midair? :D Yes, pack mud around it when you do the preslope, and yes, pack something in the open cavity (spray foam works well).

      Reply
  • Bill

    when i poured my first slope pour, i waited a week for it to dry. now i find it to be crumbling in several places. will going over it with thin set solve the problem? or do i need to rip it all out and start over? :bonk:

    Reply
    • Roger

      Hi Bill,

      Stop rubbing it! :D You can go over it with thinset if you want to, that will take care of it.

      Reply
  • Dave

    Hello there. Just curious after laying the preslope does the liner and top bed need to be installed within a certain amount of time or can it wait a week when I have more time

    Reply
    • Roger

      Hi Dave,

      You can wait as long as you need to.

      Reply
  • Richard

    Thank you for your informative site. I’m building a curb on concrete as you have pictured here and note that you apply thinset with bricks on top. Should the bricks then be covered with Redguard and then tiled, or is mortar also needed on the bricks? My pan is already properly sloped in the slab and I will apply only Redguard to that.

    Thanks.

    Reply
    • Roger

      Hi Richard,

      You can go over it with redgard and tile, or you can mortar it in. Either way works fine.

      Reply
  • Ruth

    The mud bed was installed over a shower pan with kerdi on the walls. Can ceramic tile be installed directly on the mud bed?

    Reply
    • Roger

      Hi Ruth,

      I don’t know what you mean by ‘shower pan’, if you mean a rubber liner then yes, your tile can be bonded directly to that mud bed.

      Reply
  • Rick

    Hello, I’m installing a 36″ linear drain in a concrete slab by grinding out the slope toward a wall. Question is can I apply thin set and mud directly on the slab to smooth out my slope. Does the mud have to be a specific thickness before applying topical water proof

    Thanks Much!

    Reply
    • Roger

      Hi Rick,

      Yes, you can. Deck mud has to be a minimum thickness of 3/4″.

      Reply
  • Bryan Hayes

    Pic 2 from an angle…

    Thanks

    Reply
    • Roger

      As long as you use thinset between the layers it will be monolithic. :)

      Reply
      • Bryan

        So do I apply the thinset and then wait for it to dry before laying the additional mortar bed on top? Or do I lay it before the thinset dries?

        Reply
        • Roger

          No, you set the new mud in wet thinset so that when it cures it bonds the two together.

          Reply
  • Bryan Hayes

    Here are some pics to supplement my last question. My first choice would be to add another layer on top of this one, but I had read somewhere that you want your mortar bed to be “monolithic” and poured and cured at the same time. How important is that? Pic 2 on its way…

    Bryan

    Reply
  • Bryan Hayes

    Hi Roger,
    Thanks so much for sharing your wisdom here! I laid the pre-slope slab yesterday and put the liner on top to test it today and found the slope is not quite steep enough to direct all the water to the drain. There are no major dips or high spots though. Would you recommend my pouring another steeper layer of mud on top of that one or chiseling out the first and starting over from scratch?
    Thanks,
    Bryan

    Reply
    • Roger

      Hi Bryan,

      You can just put a steeper slope on that one as long as you put thinset beneath it to bond it to the original.

      Reply
  • John

    I have hardie backer (applied w/thinset and screws) on the shower floor which started as 3/4 inch plywood. Should I lay roof paper, then do the preslope or can I just apply the preslope material on top of the hardibacker without wire mesh?

    Reply
    • Roger

      Hi John,

      It would actually be better to install thinset over the hardi, then your deck mud. That will give you a bonded mud bed.

      Reply
  • Hank

    Is the drain flange attached to the plywood subfloor or the top of the pre slope?

    Reply
    • Roger

      Hi Hank,

      The bottom flange is attached to the subfloor.

      Reply
  • Jaime

    Hey Roger,

    So, I made the single slope to the linear drain, working hard to get the mud top to bottom slope smooth. I thought it all went well until it dried but then I noticed I had a small crown in the middle of the slope running top to drain.
    It has about 1/4″ gentle trough running top to drain, half way to each side wall, on each side of the crown but still slopes to the drain well. You can notice it when standing on it, but it is very mild.
    I have already put Kerdi membrane and it is watertight.
    QUESTION: Now the director of the household has decided to change the floor tile selection from small mosaic to large format floor tiles: 12″ x 24″.
    1. Should I smooth thinnest and let it dry flat into the troughs before setting tile? Or…
    2. Should I put another Kerdi over the floor and make it flat by allowing the thinnest underneath to fill the inconsistent areas, or…
    3. Should I use a “thick” thinnest mortar under the tile, with tile flattening clips, allowing the mortar to fill the differences on the Kerdi that is there now?
    I appreciate both your Tile Tip and Kerdi books! Full of advice and tips giving me confidence to tackle this job!
    Thanks! :-D
    Jaime

    Reply
    • Roger

      Hey Jaime,

      I would do number 1. Float it out with thinset (provided it isn’t over 1/4″) then set your tile. My second choice would be number 3, with the lippage clips.

      Reply
  • Curt

    Roger,
    Let me start by saying that reading your articles has been very helpful on my project.
    I am installing a shower in my second floor attic space. It is 36″ x 60″ with a center drain. My question is should the outside perimeter of the shower be level on all 4 sides or should my floor slope be a constant 1/4″ per LF in all directions which would make a dip in all 4 walls as the corners would be higher than the center of the walls by keeping the rise to run consistent.
    Any recommendations or comments would be welcomed.

    Reply
    • Roger

      Hi Curt,

      The perimeter should be consistently level.

      Reply
  • Richard

    I’ve put in my preslope but I just noticed that there is a small area which forms a little cup. How can I fill that so the liner won’t sag into it? Thanks.

    Reply
    • Roger

      Hi Richard,

      Either mix up a little more deck mud or fill it with thinset.

      Reply
  • JoAnne

    Hi Roger, I have a contractor who is a master plumber who is installing 2 new bathrooms and noticed he did not use a shower pan liner and already tiled. I did see backerboard on the floors and on the walls. Is this ok not to have a liner?
    Thanks,
    JoAnne

    Reply
    • Roger

      Hi JoAnne,

      Absolutely not, unless he has a topical membrane over the shower floor, something like kerdi or hydroban. Your floor NEEDS a liner.

      Reply
  • Jaime

    Roger,

    So I threw the Coors can out, got myself a bona-fide drain plug.

    Just got your Kerdi shower book – it’s great!

    Now in planning the shower floor here is the set up:
    -Wooden floor (second story shower)
    -Linear Kerdi-Drain at one end.
    -Planned single slope floor to the drain.

    1. Can I put 1/4″ Hardi-Board down and screw it to the floor to be my cleavage plane, then apply thinnest under the deck mud?

    2. Does it make any sense to cut out Hardie Board slope guides to have set on the sides and part of the final bed – the sides of the mud, guiding my slope formation with the ol’ 2×4 (mine has a hole in it too, just like yours, but maybe not as big… oh… sorry…) These would be ‘rails’ that would also be part of the floor.

    3. Did you say no Green Sheetrock under Kerdi membrane? Really? I just bought a bunch – figured it was better than plain sheetrock. How come?

    4. For the odd size penetrations (insert lame joke) such as body sprays, should I use the silicone sealant ring to seal the tile to Kerdi? The pre-made Kerdi seals are too big or too small…

    Thanks!
    :wink:

    Reply
    • Roger

      Hi Jaime,

      1. Yes, but you’ll need to put thinset under the hardi as well.

      2. You can if you want, it won’t hurt anything.

      3. Yes. They’ve found that the green stuff actually FEEDS mold (rather than preventing it) more than regular drywall.

      4. Yes, I really wish they’d make more sizes. The silicone will work fine.

      Reply
  • wayne

    I am confused about what you are saying about the depth of my shower base. I am enclosing two quotes.
    How to Create a Shower Floor – Part 1
    Your finished floor (after your liner and top mud bed are installed) needs to be 1″ to 1 1/4″ thick at the drain.
    How to Create a Shower Floor – Part 4
    What we will now be doing is fabricating your top mud bed directly over the top of your waterproof liner. The top bed will be 1 1/4″ to 1 1/2″ thick – consistent throughout from the drain to the wall
    How can the finished floor be 1″ to 1 1/4″ thick if the top bed is 1 1/4″ to 1 1/2″ thick? Did you mean to say the preslope should be 1″ to 1 1/4″ making the finished floor 2 1/4″ to 3″ thick at the drain?

    Reply
    • Roger

      Hi Wayne,

      Provided the finished floor – both beds – is a minimum of 1″ thick then it doesn’t matter. The reason I put the first part is because I changed it after everyone was having issues with the drain being installed flush with the subfloor – so I changed that and failed to change the thickness in part 4. You’re paying attention, though. :D Thanks for pointing it out, I’ll get it fixed.

      Reply
  • Roy

    When using the Schluter pre-formed shower base, is it necessary to put the water proof membrane under the base? The Schluter video shows the thinset mortar applied directly to the plywood. Thanks.

    Reply
  • Robyn

    I am expanding the size and changing the layout of our 1959 hall bath from 7×9 to 9×9. Under the existing 1″ square white mosaic tile in the original portion there is one inch of concrete buildup. I may need to remove the tile but am wondering that instead of removing all that great concrete and just putting it back, if I can just membrane the new portion and buildup up the floor to match the old one, forming the required contour around the floor drain before i lay new mosaic tile. The shower will be an open floor shower with a curtain so there will be no shower enclosure or floor pan. The floor drain will be the old tub drain, centered into the new area. It will be about two feet from the new wall, and two feet from the old tile. The other walls will be 4.5 feet away. Thank you for your advice.

    Reply
  • doug

    just to let you know that this diy’r is learning alot from you and your effort is much appreciated.

    Reply
  • Darien

    Roger, I have learned a lot from your elf! I have some questions for you regarding a walk in shower we are attempting to do in our basement on a concrete floor. We are going to use a liquid topical membrane. Do I need to just install the preslope then use the topical membrane then tile or do I need the preslope then topical membrane then final slope with deck mud then tile. I guess what I am asking is if I need the final slope? One of our shower walls is block foundation wall. Will I need to attach cement board to the block wall or can I just use topical membrane on it and tile it? Will I need a kerdi style drain or can I use a regular drain? Any help and info would be greatly appreciated! I see you are from Fort Collins. I am in McCook Nebraska. Maybe I could just have you come and install the shower correctly for me! Ha! Ha!

    Reply
    • Roger

      Hi Darien,

      You do not need the top slope, you do need a topical drain. You should attach backer to that block wall (the wall is gonna move – A LOT). If you haven’t yet checked out the library the manuals in there can answer all your questions and give you step by step instructions.

      Reply
      • Darien

        Roger. Thank you for your response! I do not understand what you mean by a topical drain(what brand?). I have a drain we had already bought for the shower with the weep holes in it. It is an Oatey brand to be used with a liner. My drain pipe is 2 inch pvc pipe in my basement floor. It used to have a Durastall prefab shower there. It looks like I may need to jackhammer my concrete floor to cut the drain pipe low enough to make the drain work. Exactly what drain do I use if only doing the first slope? Do I do the first slope then the liner then attach tile to the liner?

        Reply
        • Roger

          A topical drain is one such as the schluter kerdi drain. You stated that you are using a liquid topical membrane – if you are then YOU DO NOT use the liner in the floor, the liquid is your waterproofing.

          Now I’m not exactly sure what you’ve got going on there. :D

          Reply
      • Darien

        So I can use the schluter style drain. How does the flange of this style drain tie into my liquid membrane? Do I need some type of material to attach to the flange or do I just install the drain do my slope with deck mud then seal it up with red guard liquid topical membrane? Do you install the backer board on the shower walls first to the existing floor then do your deck mud or do the deck mud then backer board to the walls leaving a gap? Would this gap need sealed? Sorry for all the questions. I only want to do this once and I want it to be correct the first time! I owe you some beer! Oops, I mean some milk! At least my dog hasn’t exploded yet!

        Reply
        • Roger

          Hi Darian,

          The drain is simply installed into the mud deck flush with the top of the deck, then redgard is painted over the entire floor up to the center of the drain (over the mesh) creating a uniform waterproofing layer. I install the boards first, to within 1/4″ of the floor, then pack the deck right up against it.

          Reply