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:

Alan

I have looked through your blogs and your replies to people. I can’t find any reason not to replace the rotted out floor in my mobile home shower and build a mud slope, install backerboard on the walls, apply a liquid membrane, then tile it. What was in there was a small shower with very thin wallboard, like masonite, which is rotted up to about two feet. It had a cracked, leaky plastic shower pan placed on particle board. There’s no trace of any moisture barrier. It was only caulked. I find the installation horribly poor and don’t want to buy a replacement pan and shower surrounds. I want to do the job myself.
I had planned to reinforce the floor joists with sister boards and cross supports to make it strong and level. I want to use 3/4 exterior plywood for the new floor. I’ve downloaded your information pdfs and want to go ahead with the job.
Do you agree that it should be fine to build a shower, using your instructions, for my mobile home? I ask because I haven’t found anyone else doing this.
Thank you,
Alan

Reply

Roger

Hi Alan,

Absolutely no reason at all not to do it. Provided you can shore up the framing to support a proper installation there will be no problem with it at all.

Reply

Kristina

We have a 32×36″ concrete shower in our basement that has been painted with blue concrete pool paint. It is not smooth and looks unfinished and rough. I would like to finish it. I am not sure how to go about it. Someone said just tile over the existing surface but that seems unwise since the paint has already chipped on the floor. The corners are not clean angles. The shower operates fine with water draining into the drain as it should. If we apply backer board, how do we attach it to the walls so that it doesn’t decrease the size of the shower too much and is straight and level?

Reply

Kristina

update. The size is 36×40 and the walls are made of concrete brick and then painted. It looks as if the floor has some sort of liner at the point where the walls and floor meet which I can see the faint outline of through the thick pool paint layer. Would it be easiest to just tear out the shower and start over? I hope not but am starting to wonder.

Reply

Roger

Hi Kristina,

You can not install backer over your concrete walls. You need to scarify the existing finish, then use a waterproofing liquid or fabric over the concrete, then install your tile directly to it.

Reply

Mimi

Hello Mr High Elf of the Floor forest.
I sent a first message but I guess it got erased automatically (because links).
I am building a new shower, but I want to use a linear drain, the type that drops into a drain for topical membrane (not the laticrete kind, because I am not rich :whistle:
The shower is 36″ x 60″ and the drain would be in the center, along the short axis.

I was wondering how to do a preslope and final slope in that situation. The instructions that come with the drain are garbage, with no slope install at all, and I want to do it properly. I made a few drawings that would make all of this clearer but I’m not sure how to send them – they are upladed to imgur (SparklesAndRobots), but I think putting the link here will block my message again as spam. Any other way to send you links?

In any case my idea is to make a gutter where the drain will go, so in the center of the shower along the short axis.
Preslope: a 1/4″/foot slope in the gutter (starting with 3/4″ of mud under the drain). On each side of the gutter (the drain is in the center of the shower) make a ‘strait slope’, with the lowest point along the gutter (and a tad higher then the highest point in the gutter), and the highest point parralel to the gutter at the curb (still following a 1/4″/foot slope)
Then put membrane + top part of drain.
For the final slope, I need to level the gutter so that I an install the drain on a flat surface – so I’d add only 1/4″ of mud to the highest point of the preslope, but 3/4″ in the center, to have my drain (and all of the gutter) at a height of 1 1/2″ total. I’d add an even 3/4″ on the two ‘strait slopes’ to keep the same slope as the preslope. This all works out that the drain, once installed, should be about 1/8″ below the neighbouring tiles.

It’d be so much clearer with the drawings!!! :bonk:

But if you can figure out what I am saying, please let me know if you think that would work out. THANKS A BIGILLIONS!!!

Reply

Roger

Hi Mimi,

I’m confused, you said you want to use a linear drain for topical waterproofing, but you’re describing the method used for a traditional linear drain – which is it? If it is a topical drain (I understand it ties into the regular drain base) the weep holes are not utilized, you only need one slope, not a bottom then a top, and you don’t need a membrane. If the membrane you are speaking of it a topical membrane then the tile is bonded directly to it, you don’t need another mud bed over it. What specific drain do you have? Do you have a link to it? You can place one link, any more than that and the spam nazis blow it up. :D

Reply

Roger

I just found your links. Your plan is fine depth-wise and all that. It is not a topical drain. :D And for some reason (because they don’t know any better) the literature on their drain on the site does not include a pre-slope, so you are already doing better than them. :D

Reply

Mimi

Thanks a bunch about pulling my mail from the spam and checking links (I assume), and sorry about getting garbled about topical vs traditionnal. It’s a lot of info to process!
Your site is wonderful, I don’t know if I would have had the courage to jump into a project like this without proper guidance, and I found pretty much everything I needed (and much more) on this site. It is very generous and selfless of you to share your knowledge like that.
Hugs from Canada!

Reply

Leave a Snarky Remark

***PLEASE READ THIS FIRST!***

If you have already posted a question about your project and you are leaving an additional comment or asking another question - please do so as a reply to my answer to your last question.

Below every comment is the phrase 'Please click here to reply to this comment', just click on that and leave your next question.

If you post an additional question here it will show up as a new topic and thread. I have over 15,000 comments on this site (seriously), I can not go through every one to find the project or question you may be referencing.

HELP ME HELP YOU!

Thanks.

;) :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)