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

Previous post:

Next post:


Hi, Roger.

First off, let me say that I read through your waterproofing manual, and I really found it helpful and very well written. I work in the marketing and training field, and I was impressed with how well you could take a relatively dry subject and make it interesting and even entertaining. It was a quick and informative read.

I apologize if my questions are already answered on your site, but with three little kids at home and another on the way, I have very little time to peruse the site for clarifications. :bonk: So thanks in advance for your patience.

So I have three questions: one is related to waterproofing, one is related to information I’ve received from contractors, and one is related to shower seats.

1) Topical Waterproofing Transitions: In your waterproofing manual, you suggested the paint-on options as possibilities for the topical waterproofing application on the walls (and the shower floor, I believe). I really like this idea as to me it seems the most foolproof. My question is how you would handle the transition from the walls to the shower floor. You made a mention in passing that some of these topical applications require a fabric-like transition, but I didn’t really see anything more in that vein. Perhaps this is covered in your detailed manual, but I’m not quite ready to make the purchase as we are still considering using a contractor to build our shower. Which takes me to question 2….

2) Contractor Tales: I’ve gotten three quotes from contractors to finish my basement bathroom. One of the contractors works with the general contractor I used to help finish my basement, and the other two were recommended by a tile shop. I have received quotes to complete the job from $900 to $2300 to $3000. So here’s are my questions. I talked with my contractor about the process his guy (the $2300 quote) would use to build the curb and install the shower pan, and he described the process as follows:
– The PLUMBER usually builds the shower pan and curb. The curb is built with treated 2×4’s, 2×6’s, etc. stacked on the flat to whatever spec the homeowner desires. The plumber then lines the concrete floor with the rubber membrane which goes up the studs about a foot and is secured there. Then mud is applied to build the slope / shower floor. Then tile goes directly on top of the mud. This made me uneasy having read through your waterproofing manual and just having looked at your instructions of building a shower curb using bricks if on concrete. I’m not clear on whether the cost for the pan / curb was included in the $2300 or not — waiting for an answer on that.
– For walls, the cement backerboard can be run down to the shower floor and then tile can be installed directly to that using typical tiling methods. He said in his personal shower, he had it built using wire mesh and cement and then the tile installed directly on top of that — no membrane. This also made me uneasy.
– For the general bathroom floor, my contractor’s tile guy said that he would need to use floor leveling compound to make the basement floor level before tiling the rest of the bathroom. The other contractors said that wouldn’t be necessary. There’s not a huge pitch to my basement floor, but there is some. And there is some unevenness to the floor because of the floor break we had to do to install rough plumbing. I’m not sure the leveling step is necessary, and I was thinking we could just install the tile directly over the concrete, using the thinset to even out any unevenness from the floor break. — But then I saw something on your site about needed to have an underlayment even on a concrete floor, so now I wonder if leveling compound would be the right choice.
– I guess I always thought it was safe to assume that contractors (especially the one I know personally) know what they’re doing since they do this stuff all of the time, but now I’m swinging back the pendulum to “Should I just do it myself?” I am very meticulous and detailed, but I don’t know if I have the time to get this done before baby #4 comes and insanity ensues. :dance:

3) In looking through your post on shower benches, I didn’t see any description of how to build a triangular corner shower bench over a concrete floor. I saw the description of a regular rectangular bench, but I’m wondering what material you’d suggest if we want to do a small corner bench. I assume cinder blocks would not be ideal in that case. Maybe just a small square-ish bench would be easier than a triangular one.

Anyway, that’s my novel. Sorry it’s so long, but hopefully it helps give you some context of the things I’m thinking through. I really appreciate any input you can give. Thanks!



Hi Stephen,

1. The transition and use of fabric reinforcement depends on the particular membrane you are using – some require it, some do not. It is covered in the manual.

2. There are two red flags with his shower floor method – pressure treated wood should NEVER be used beneath a shower curb, it will dry out and warp / twist, and there is absolutely no mention of a preslope (and that the plumber does it, but that’s code in certain areas – they rarely do it correctly). No waterproofing method on the walls (backerboard is not waterproof). If he has mud walls there is (supposed to be) roofing felt or tar paper behind it – that is both a cleavage membrane and a waterproofing element in mud walls. I always use an underlayment to separate the tile from the underlying structure – concrete included. I normally use ditra, it has many more advantages than just slc. Your floor, however, does not necessarily need to be LEVEL, just FLAT. Some variation can be compensated for as the tile is set.

I wish all contractors knew what they were doing. I try to keep an open mind and just convince myself that most were simply not trained correctly.

3. You can build a triangular corner bench out of cinder blocks (standing upright) and filling in the gaps from the edge of the block to the wall with wall mud (deck mud with lime in it to make it sticky).

After the 2nd kid there is no new insanity, it’s just the same insanity repeated. :D


Leave a Comment

;) :wtf: :wink: :whistle: :twisted: :suspect: :shades: :roll: :rockon: :oops: :lol: :lol2: :lol1: :idea: :guedo: :evilb: :evil: :eek: :dance: :cry: :corn: :cool: :censored: :bonk: :arrow: :D :?: :-| :-o :-P :-D :-? :) :( :!: 8)