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

{ 691 Snarky remarks… add one }

Leave a Comment

  • Travis

    Roger, excellent resource you have here. I used info on your site before to rip out a fiberglass shower and install a tiled shower with the proper layers. It came out great, thanks. Now I am GC’ing and building my own new house and I want things done correct, so I do a lot of work myself and have a couple questions if you might could help. This may be hard for me to explain, but I’m going to try. This is a concrete slab foundation. Shower area is about 6’x6′ walk in and was poured with 2×6 forms set inside other forms to recess it down about 5.5″. They didn’t smooth/finish the floor like the rest of the slab so it is very rough with ridges, imperfections, etc and lines in it. So, 1st question is, I want to raise the floor by about 4″. I should mention the plumber also used those plastic dirt filled square boxes around the pipe. So when I pull it up, there is about a 1′ x 1′ box another 10″ or so deep with drain pipe in center. Can I just glue the drain 1 1/2″ or so up higher than slab level and use pre-slope to raise the height of the slab? So pre-slope deck mud would be 1 1/2″ thick at drain and 3″ at wall. Then place liner, then post slope, then tile. I know this might only end up around 1 1/2″ curb, but it should be ok for the size of this shower. Hope this all makes sense. Also, since it not a smooth finish, do I need to pour a skim coat of concrete and smooth, then thinset or just use thinset or can I just pre-slope mud right on top of this very rough concrete? Thanks in advance for your help.

    Reply
  • Mark

    Hi, I am building a traditional pan with linear drain across front wall. It will be approx. 5’x5′ using 12″x24″ tiles. When I lay my top layer sloped should I use a level height all around or leave the side sloped and just trim the bottom layer of wall tile to fit the slope. If I keep side wall level with the top of slope will I have trouble with my large floor tiles?
    Thanks

    Reply
  • Tim

    Roger,

    I am building a 4×6 shower on subfloor. I am planning on using Redgard so I will have just a single mortar bed. The drain is about 12- 18 inches from one end. my concern is that the 1 1/2 inch slope will be too steep on the short side. should I be? should I do something different?

    thanks!

    Tim

    Reply
  • Tim

    Roger,

    I have a 4×6 shower. the drain is only about 18″ from one side. I am planning on using Redgard so there will only be one mortar bed. my concern is that the 1 1/2 ” slope will be way too steep on the short side. should i be?

    Thanks!

    Reply
  • Sean

    We have a basement shower on concrete floor with ceramic tile attached to it. Problem is water does not drain right. How can I address the slope issue without tearing old out as its brand new? Or do we buy a squeegee and life with it?
    Thanks.

    Reply
  • John

    Hello Roger, doing a liquid topical shower/pan on concrete slab with the divot method. In your book did I see where it looks like the backer is brought down to the slab and the pre-slope was done inside the backer boards or does one have to do pre-slope first then bring backer down to pre-slope leaving small gap at bottom for change of plane and silicon?
    Thanks for all the info.

    Reply
    • John

      This is same John as above. I just wanted to clarify it would not be a pre-slope but a single layer slope. I would put Hardi backer up on the walls and the slope would be set inside the backer boards(backer being the forms for the single layer slope)

      Reply
  • Valerie

    I was wondering what size of bricks you used for the curb. Did you bond them to the concrete floor in any way? Is this a special type/size of brick you need to buy?

    Reply
    • Roger

      Hi Valerie,

      I use 4×8 concrete bricks with no holes. Yes, I thinset them to the floor.

      Reply
  • steve

    Roger,
    I have a question, I rebuild me shower floor and the slope is not enough, now I am planning to remove the tiles and add more slope.
    Question:
    can I use thinset OVER thinset to make a level high if so how much thickness can thinset easy accommodate ? or can I use concrete over existing thinset?

    Thanks

    Reply
    • Roger

      Hi Steve,

      You can use deck mud over the existing. You need to spread thinset over what you have and place the deck mud over that. Thinset is only for bonding – not building up.

      Reply
  • Dmitri

    Hi Roger, I am building a shower pan on a concrete slab and made the curb as you recommended using concrete blocks. I did the preslope and now I am ready to put the liner. my question is do I run the liner over the concrete curb to the outside of the shower? if so, how do I secure the liner to the concrete blocks? also, if the liner goes over the concrete curb, do I put a lathe over that and mud it as well?? thank you in advance for your help

    Reply
    • Roger

      Hi Dmitri,

      Yes, the liner goes over the curb. It’s the lath that holds it in place, then mud over that.

      Reply
  • Omar

    Roger,

    I put up a vapor sheild (6 mil clear plastic sheeting) behind the Durock for a shower I am doing. When I went to buy Redgard I found out I should not do both. Should I a) tear down the Durock and vapor sheild and start over, b) use the Redgard as is, or c) leave it alone and not use Redgard? Thanks. Omar

    Reply
    • Roger

      Hi Omar,

      I would leave it alone and not use the redgard. Tile directly to the backer.

      Reply
  • Mike

    Putting in basement shower on concrete. Drain line is flush with floor and cannot be cut any lower. Want to put in kerdi drain with red guard. The deck mud will be close to 3.25″ at the drain and close to 4″ at perimeter. Is that to deep? I think kerdi recommends .75 to 1.75″ depth at drain. Thanks in advance. Your manual has helped a lot.

    Reply
    • Roger

      Hi Mike,

      Nope, that’s not too thick. That’ll work fine.

      Reply
  • Steve

    Roger,
    I want to re-tile my 3.5′ x 4.5′ shower. Walls and floor were previously tiled; that’s all been taken out, including the floor mud bed down to the existing concrete base. The top of the lower flange is flush with the concrete base. The existing liner (roofing felt) was laid over the concrete and clamped between the upper and lower drain flange. Don’t know how much that helped, since the concrete base is level. Any ideas (other than busting the concrete to raise the lower flange) on installing the new liner? There was only 1 layer of mud with tile over the felt (2-1/4″ from concrete base to top of drain).

    Thanks, Steve

    Reply
    • Roger

      Hi Steve,

      You can still create the preslope down to nearly nothing at the drain if you need to. While not technically correct, it’ll be fine on the preslope provided you have a minimum of 1 1/4″ of mud at the drain for the top slope.

      Reply
  • George

    If I decide to use RedGard as a water proofing and cement board for the walls, do I still need to use a shower pan, or even create a pre-slope?
    Too many options…
    Thanks

    Reply
    • Roger

      Hi George,

      If you use redgard you only need a single slope with the redgard on it, then tile is installed directly to it.

      Reply
      • Steve

        Thanks Roger, will work it as noted.
        And thanks for all the info you provide on your site.

        Reply
  • Chris

    Uggh,
    I bought your manuals (Im excited about that) but, Ive got a bit of a problem!
    I am building a shower pan that must be accessible by a wheelchair. I cannot do a “curb” and, I am wondering how I design the pre-slope, top slope and all that good stuff. The shower pan will be approximately 60″ x 60″ and I will need to transition from the new tile surface to the existing subfloor (with a lino surface on top) Is this application covered in your ebooks I bought? I have everything-lathe, mud, membrane, drain, etc.

    Reply
    • bob

      you cut down your floor joists so when you build up your mud deck it is level with the floor….it is not for the timid…i did it last year but was just above a crawl space and could add more joists for support. here is a video giving you an idea of the project….but he does some sketchy things…no pre-slope, cutting through laminated joists……….
      https://www.youtube.com/watch?v=yEMzHWK-1t4

      Reply
    • Roger

      Hi Chris,

      I do not cover curbless showers in my book. While they can be done with a traditional method, either by lowering the shower floor substrate enough to create the slope, or creating a ‘speed bump’ of sorts, where the floor rises up to the shower threshold, then back down to create the slope, a topical method is much easier to create curbless showers.

      Reply
  • Chris

    Loved the how to!
    A couple of questions though:
    The Lathe you refer to, what is that? Plastic, metal?
    In regard to a curb, I am building a shower for a handicapped relative that will need to roll into the shower. I cannot have a curb, I can deal with the 1 1/2″ rise for drainage and, I will need to find a transition for a wheelchair to go from lino to the tile surface-help?
    Thank you!

    Reply
    • Roger

      Hi Chris,

      The lath is expanded metal. Google ‘schluter transitions’ for your transition from lino to tile.

      Reply
  • Bob

    Roger,
    HELP! I bought your book on doing a kerdi installation. I did the dry mortar base with the kerdi drain and decided to try your suggested method of removing the drain the following day to bond it with the thinset. But I can’t get the drain out now! I think I got the mortar consistency right – clumps when squeezed with no water running out.

    I’ve fiddled with it quite a bit and it doesn’t seem to budge. I don’t want to pry on it too much as I’m worried I might damage the drain or the pan.

    Any suggestions?

    Reply
    • Roger

      Hi Bob,

      Just leave it. Once you install the kerdi over it it’ll be locked in. It obviously isn’t moving. :D

      Reply
  • Joseph

    Hi,

    Roger,
    I am in a process of building a shower on a concrete floor. The size of the shower is 3’x5′ . I need to build a 5′ curb size of (60″x4″x6″) I thought to build a curb (60″x4″x4.5″) using cement as follow:

    creating a frame size (60″x4″x4.5″) and then pour cement (quickrete cement mix ready to use) instead of concrete bricks. What do you think ?

    Appreciate your quick reply

    Thanks Joseph

    Reply
    • Roger

      Hi Joseph,

      That will work just fine.

      Reply
  • Tom

    I live in Florida and both of my shower floors were built into an opening in the concrete slab. Another words, under the shower floor is dirt, not a concrete floor. I remember seeing this while the house was under construction. Have you heard of this before? How does one renovate a shower when the floor is constructed in this manner?

    Reply
    • Dave L

      Tom,
      The same shotty plumber/GC who built your house must have built mine. When I tore out the pre-fabricated fiberglass shower pan it too was basically sitting in the dirt. They didn’t bother to pour concrete back around the drain pipe and flange. What you need to do is pour the concrete back flush with the existing slab. BUT, set the new drain flange somewhere between 3/4″ and 1-1/4″ above the concrete. This will allow for the pre-slope deck mud. After you pour the slab back, go back to the top of this page and read about “creating a pre-slope”. Good luck

      Reply
    • Roger

      Hi Tom,

      Yes, I have heard of it, but only in Florida and Texas. Remove everything, begin with a solid concrete or deck mud base and build up from there.

      Reply
  • Dave L

    Elf,
    My pre-slope is going over a concrete slab. I was reading that you recommend a layer of this etc between the slab and thick set for bonding purposes. Q: Should the thin set be wet or cured prior to placing the thick set preslope? Also, have you tried a concrete bonding agent? I see that Sika, WR Meadows, and even Quickcrete makes one

    Reply
    • Roger

      Hi Dave,

      It should be wet and a bonding agent is not required (thinset is your bonding agent).

      Reply
  • Bryan

    Hi Roger,
    I started down the road to a remodeled shower stall with your manual “Liquid topical waterproofing for walls around a tub or pre-formed base”. Now am switching to a tiled floor. I am at the point of a bare slab floor, studs and no drain installed yet. What shower construction and water proofing method would you suggest and which manual(s) should I get now? Not necessarily looking for the most convenient method but the most reliable and long lasting. Thanks

    Reply
    • Roger

      Hi Brian,

      I prefer topical methods, and redgard is more foolproof than kerdi, So the liquid topical waterproofing for your shower would be the one I would go with.

      Reply
      • Brian

        Great, just to make sure, this is the manual to download: “How to Build a Shower with Liquid Topical Waterproofing on Floors and Walls”? Will it also explain how to build the shower floor from a slab base? Thanks

        Reply
        • Roger

          Yes it does.

          Reply
  • Mike

    Hi Roger,

    I inquired on Aug 2nd about a 2×4 curb and a slab drain on cement floor. I did replace both per your suggestion. Now the shower is coming along great per your instructions. Thanks so much, I’ll be recommending your book and site to others.

    Mike

    Reply
  • Peter K

    Hi Roger – Great site. I will buy your Traditional Waterproofing book now but I figure I will ask one quick question.

    In reference to making sure the floor doesn’t move you say… “On wood you can use regular metal lathe.”

    Well, I just put down a new OSB sub-floor and now I am putting down Quik-Trak for my hydronic radiant floor heating system. Once that is down, I will put a 1/4″ backerboard on the entire floor (shower stall and bathroom floor).

    Now, the 1/4″ backerboard has a grooves cut into the side facing up. They laid out in a 1″ square pattern – My question is this: Do I need to put a metal lathe on the backerboard before putting the mud down or will the grid pattern of grooves provide sufficient resistance to any movement of the floor, once the mud has set?

    Thanks for you help.

    /peter

    Reply
    • Roger

      Hi Peter,

      You do not need to put metal lath over that. The grooves will be fine.

      Reply
  • Matt

    Roger – I tried to follow your site to the best of my ability. I did make a few mistakes, but over all the shower works great.

    Here is how I built mine. https://mmmhr.wordpress.com/

    Thank you Matt

    Reply
  • Steve

    Roger,
    So if I peel the vct off the mosaics after 24hr. Cure could I still mortar them onto the floor? The reason I ask is they stay perfectly flat and I would be probably perfect in height to ensure a flat installation. I just don’t know if the cured mortar would stick to the floor setting mortar or if it would be weak

    Reply
    • Roger

      Hi Steve,

      Cured mortar will bond just fine to fresh mortar. Beyond that I’m not really sure what you’re attempting to do. I initially thought you were using the vct to heighten the mosaics, but now I’m not sure?

      Reply
  • Mike

    Hi Roger,

    Thanks for all the good insight. I’m remodeling a shower that was started but never finished and has some peculiar features. It was set up for a 2 pan liner, but an Oatey two part adjustable slab drain was installed into the cement subfloor instead of a clamping drain. Also the curb was originally made out of 2x4s. Is it essential that I switch these out? Is there any way to use the current drain with the two mortar beds sandwiched around an Oatey liner? Thanks.

    Reply
    • Roger

      Hi Mike,

      Unfortunately both of those need to be changed. There is no way to use that drain with the liner, and you CAN NOT have wood on concrete like that.

      Reply