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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Lesha

Hi,
My husband and I have turned a open carport into a master bedroom and bathroom. Due to health problems we have designed all door ways for wheel chair access. there was a preexisting cement floor that we did not realize was leveled to run the water off the side which now is a complete wall. We want to be able to roll a wheel chair in and out. the shower is 5×8. We want to put ceramic down on the floor and all the way up the wall. But first we have to fix the problem with leveling the floor. can u please help us to figure out wat to do….

Reply

Roger

HI Lesha,

If you’re just concerned about the shower portion of the floor then you need to use deck mud to slope it towards the drain. I can’t really help much unless I know where the drain and shower entrance are relative to slope of the floor.

Reply

Jesse

Hey Rog, I am looking for a little clarification in regards to the pre slope and the use of lath. You make no mention of the use of lath in the construction of a preslope on a concrete floor however on a wood floor the lath is required, over plastic or roofing felt, makes since. My question is if You, the floor elf, were constructing a shower on a concrete floor would you forego the use of lath? Just use a thinset slurry and then deckmud? or is the lath prefered as I am sure it would add strength to the mud and to the overall base of your shower. I ve used lath before in construction and have always felt it difficult to work with if it isn’t firmly flattened and fastened or stapled in place, which would be difficult with a concrete floor. Anyway, Just wondering how you would approach this, as I would feel much more comfortable about my shower base if it had the floor elf stamp of approval!

Many thanks Rog, I think it’s great your willing to give up your time to help others, Lord knows folks need it!!

Reply

Roger

Hi Jesse,

I normally don’t use lath to strengthen the mud floor unless the shower is over 30 square feet or so. Over a slab a thinset slurry is sufficient to hold it in place and it has plenty of strength.

Reply

Keith

Roger,

I’m redoing a bathroom; completely gutting it down to the studs and joist. Can I do the preslope with framing the subfloor with the slope and then the liner or do I need the preslope to be mud?

Thanks,
Keith

Reply

Roger

Hi Keith,

It needs to be mud.

Reply

Simon

Hi Roger,
I am planning to remodel my shower it’s 31 x 40” and I need professional advice.
My wall studs and bottom plate are very ,very , very bad.
I must reinforce the bottom plates and wall studs. Screw or nail a new piece on the top of bottom plate also using PL400 or liquid nail(what product is better?)
Wall studs using sandwich style – apply PL400 or liquid nail on 2 sides of 2×4 new stud ,one which go to the wall another to the damage stud. How should i secure them, should I use nail , screws?
or should I just drill the 3 halls and screw them with the bolts?
I am going to use KD 2×4 #2 lumber.(or PT)
Floor:
I want to order custom shower pan , white one piece no tile.
Do you know where I can order good one?
Also how to prepare the floor for pan?
Walls are going to be ½” hardiebecker, 2” tape ,Laticrete thin set 253 gold, and Hydro ban or Red Guard
(2 cowers) should I do this.
And what product is better and easy to work with?
I want to use frameless doors , in this case I must do the curb right?
To make the curb 3or 2 2×4 lumber tape, hardiebacker and hydroban.
Tile:
Porcelain 12×12.

Thanks,
Simon

Reply

Roger

Hi Simon,

Any method you mentioned to fix your framing will work. pl400 and LN are comparable to me in that application. Either will work fine. I don’t know where to order a solid one-piece shower base, I don’t do pre-formed bases. There are a lot of options available. I prefer hydroban, but either will work and are mostly just as easy as the other. Yes, you must do the curb right, whether you are using frameless or not. :D Yes on the 2×4′s, no tape. Hardi and hydroban are perfect.

Reply

Simon

Thanks Roger,
How about thin set 253 Gold or 254 Platinum for porcelain.
You said no tape, but hardiebacker says to fill the joints with glass fiber
tape and thin set.
Also what the best way to secure the studs.

Thanks,
Simon.

Reply

Roger

Like I said, any of the methods you mentioned to secure the studs will work. I would likely use pl400 and bolt or screw them together. No tape on the curb. Hardi also says it’s fine to install without a vapor barrier – they are selling to multiple trades, not just tile. They will not cover everything. 253 or 254 will work great. They are both very good.

If you have any further questions can you please post them as a reply rather than a new post? Thanks.

Reply

Tom

I removed the fiberglass stall kit. The bathroom floor has creimic tile. The tile does go under the fiberglass kit. The tile is of very good quality. What do I put on top of this before the mud floor?
Thanks,
Tom

Reply

Roger

Hi Tom,

You can scuff up the surface of the tile and use thinset to bond the mud deck to it. Or you can remove the tile.

Reply

Lisa

I tried this once today, but I don’t think it went through … if it did, my appologies.

Problem – we knew to put unsanded grout on the walls and sanded on the shower floor (we went with a pebble floor); However, we changed our mind on the floor color and I didn’t double check when my husband returned from the store and mixed the grout. I just smeared that stuff inbetween all ofthe spaces and spent hours trying to wipe it all back off. Two days later, it dawned on me that we used unsanded grout!
Question – What can we do? Am I going to have to scrape all the grout out and redo it? Will this compromise the pebbles? Do I have to take ALL of the grout out? OK – that was more than one question. Sorry, but I’m a bit frantic now … we were so close! Thanks, Lisa.

Reply

Roger

Hi Lisa,

Oops. :) The grout needs to be removed down to where you have 2/3 of the sides of the pebbles showing (where there will be grout). However, if the grout has been installed, and is NOT shrinking and pulling away from the sides you may be just fine. The only reason to use sanded grout is to fill larger grout lines. The sand prevents the grout from shrinking. If it’s good after 28 days you’re just fine (that’s the amount of time for a final cure).

Reply

Alex

Okay, so we have created the curb and pre-slope and installed the liner. We are having a little trouble with the balloon trick but I am going later to get a thicker balloon so that it wont burst on the transition from the drain. When al the water drained, I did notice that water was puddled in one portion of the floor. It was not much but is this something I should be concerned about or should I continue the leak test and install the top-mud layer?

Reply

Roger

If it is puddling in a corner or against the wall then you need to pull it back and fix the slope in that area. If it is just a small area somewhere between the wall and drain it’s up to you whether or not you want to fix it. I would, but I’m an anal bastard. :D

Reply

Alex

Thanks Roger.
Since it will only require a small amount to build up that one section, should I make mud and spread some thinset or just use thinset? :bonk:

Reply

Roger

Just using thinset is fine.

Reply

Bill

Hi, We removed a tub and now we have shower size of 36″ x 67″. the drain is 18″ from the front wall, with furthest corner being 4′ 6″. Using your method the front wall appears rather steep while the furthest has the correct slope. Is this an optical illusion or is there another way of calculating the slope? Also how does the deck mud stick to the liner? Is thin set also used?
In addition when the tub was removed the slab under the tub has been chiseled down an 1-1/2″ (the thickness of a 2 x 4). Do I need to level the floor or can I began the preslope steps here on the existing substrate.
If this is too hard for a novice, do you a tutorial on how to put the dam the tub back? Thanks Bill

Reply

Roger

Hi Bill,

It’s not an optical illusion. With an offset drain, if your perimeter is level your slope will not be consistent. You can always have the perimeter NOT be level and just run 1/4″ / foot to every wall, but the bottom row of tile will be more noticeable than the steep slope on the end. Entirely up to you, it’s fine should you choose to do that. You can just build the preslope right over that slab, it’ll just be thicker.

Reply

Jennifer

I am replacing a fiberglass shower with a custom concrete floor. You instructions are great for every step. My one question before I get started is do I attach the lower part of the drain (im using the 3 piece drain system) directly to the concrete subfloor? Or do I leave it up a little. If I leave it up a little how do I screw it into the concrete subfloor?
Thanks,
Jennifer

Reply

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