How to Create a Shower Floor – Part 1

by Roger

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

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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?



Hi JoAnne,

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




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…




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.



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?



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.



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.



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.



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



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!



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.



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?



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



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!



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.


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