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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Jenny

My shower floor has a corner which water always stand and does not drain into the center hole.How can I fix it? Thanks

Reply

Hannah

When using a liquid waterproofing membrane, how many square feet will a gallon usually cover?

Reply

Roger

Hi Hannah,

Normally 35-40 square feet with the proper thickness.

Reply

Michael

Thanks for all the great info.

We’ve chosen to use a 30″ x 3″ linear drain in our walk in shower, located against the wall with the controls & shower head. Any thing special I should keep in mind as we build up the pan? Same process / thicknesses, etc? I have a standard drain assembly (at least the bottom section w/ clamp ring) in place now, about to secure to incoming 2″ drain pipe.

Reply

Roger

Hi Michael,

Nothing really, except it will be a flat plane, with a consistent slope to the drain, rather than a shallow bowl-shaped base.

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Bill

i find your site very informative. I am building a shower where I took my tub out. Three sides are walled. I am going to take it down to the studs and start from scratch. It has a concrete floor. Are you saying I have to put bricks all around the floor or just for the front curb? If just for the front curb then what stops the bottom wall plates from swelling as you discribe? If I put bricks all around won’t that leave me with a lip at the bottom of the shower walls when I get finished?

Reply

Roger

Hi Bill,

Just for the front curb. I don’t understand the question about the bottom plates swelling. If your shower is waterproof nothing will swell. Regular seasonal expansion happens, but not enough to affect anything in a properly built shower.

Reply

Daniel

Curb and pre-slope:

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.

I’m confused here: I’m building a shower pan over a wood floor, and will waterproof with Aqua-Defense. I do not see anywhere in your description of build a shower pan, the instructions for doing a single layer of deck mud, and the proper installation of the shower drain??? Also, if I use a single layer of deck mud for my shower pan, can I use a standard three part drain with weep holes? Very confused on this issue…thanks!

Reply

Roger

Hi Daniel,

That’s because this set of articles is for the double-layer liner type of pan. If only doing a single layer do it just like the preslope instructions, only with the final thickness. You should use a topical drain if utilizing AD as your waterproofing. You CAN use a clamping drain, you just need to google ‘drain divot method’. That method is also covered in my manual on liquid topical waterproofing.

Reply

Craig Wagner

ou 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.

What if my floor is concrete and not wood. How do I adhere the plastic or tar paper.

Thanks a lot
Craig

Reply

Roger

Hi Craig,

That is only over wooden substrates, you don’t need that, or lath, over concrete. You would use thinset over your concrete to bond the deck mud to it.

Reply

matt

Roger,
I have seen a methodology where the pvc liner gets “tucked” in the corners in a small gap between the studs.

Your method is to notch the stud and fold the pvc in the corners.

are both acceptable is one preferred?
thank yet again

Reply

Roger

Hi Matt,

Both are completely acceptable.

Reply

Keith

Hi Roger,
Thanks for this excellent site which is the only one that seems to bring everything together with enough detail to actually enable doing the job. I’m confused though on floor thickness, with the two comments below extracted from part 1 and part 4 . Will the final floor thickness not be 2 inches at the drain, being about 3/4 inch for the sloped layer and 1 1/4 for the top layer? or am I missing something along the way?

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.

Reply

Roger

Hi Keith,

No, you aren’t missing anything, I just don’t explain things well sometimes. The part one – 1″ – 1 1/4″ thick, is the minimum. Ideally yes, the finished assembly would be 2″ thick, however, that requires that you are able to have 1/2″ – 3/4″ thick on the preslope at the drain. If the flange is directly against the substrate it will be much thinner than that. The thickness of the top deck at the drain is the imperative portion.

Reply

Glen

I like the look of bare concrete flooring and want to use it as a shower floor. It’s an existing tiled shower, but we don’t like the look of the tile.
What kind of mix should I use, and can I go right over the existing tile?

Reply

Roger

Hi Glen,

I don’t know anything about using concrete as your wear surface. Google ‘waterproof concrete’, that will get you some basic information.

Reply

Bob

I have a shower built in my basement with the drain slope, I would like to tile the shower, its is all cement walls and floor. Can I just tile over the cement? Thank You, Bob

Reply

Roger

Hi Bob,

You can use the concrete as the substrate but you’ll need to cover it with some type of topical waterproof membrane like kerdi or a liquid membrane like hydroban or redgard.

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Randy

I am in the middle of building a custom shower and wanted to ask if it would be a good idea, as an added layer of waterproofing, to redguard the top layer of the mortar bed? I have installed the waterproof membrane on top of the first layer but wanted to know if you would recommend this technique in addition.

Thank you!

Reply

Roger

Hi Randy,

No. It may cause a mold sandwich and your weep system will not be able to function correctly.

Reply

Derek

Hey Roger, very very much enjoy your site. I am a renovator that has inadvertently become a tile shower guy quite often and a question is burning me. We like to use Hardiebacker for shower walls due to it’s stiffness. We also like to give customers the best product possible. Do we need to put kerdi over the hardiebacker to be doing it right, or is the hardiebacker enough (I assume we would still maybe kerdi the seams and corners)? Putting kerdi over hardiebacker sucks because the board dries out the mortar so quickly.
Also, I was told from our tile supplier to use Profix Multi-flex, a polymer-added mortar, to embed kerdi or ditra, and use R20 Flex, unmodified, over top to set tiles. Is this correct?
Thank you so, so much in advance.

Reply

Roger

Hi Derek,

You need to waterproof the hardi in some manner. Hardi is not waterproof – at all. It will soak in water. You either need a membrane over the surface of it, like kerdi, or a membrane behind it between the hardi and wall framing, like 4-6 mil plastic or roofing felt.

Unmodified thinset is used for everything in a kerdi shower over hardi.

Reply

Olga

Hi! Is it possible to use hardie backer board on the shower floor instead of first layer of mortar and waterproof membrane? Meaning plywood, then hardie board, then a layer of mortar to create a slope, then red guard, and then tile. The guy at Home Depot recommended it saying its a new way of doing it, and we are just not sure. Please help! Thank you!

Reply

Roger

Hi Olga,

It sounds like he’s trying to sell you a lot of stuff you don’t need. :D You can simply create a single layer of deck mud and waterproof it with redgard (provided you have the correct drain or use the ‘divot’ method) then tile. You don’t need the backer under it. And that method has been around for about 25 years, there’s nothing at all ‘new’ about it. :D

Reply

Bobby

Why do you not like to use the kerdi system for the shower base, is it not a sound product?

Reply

Roger

Hi Bobby,

It is a VERY sound product. I’ve seen people drive forklifts over it after is was tiled (true story). The only reason I don’t use them is they don’t come in the sized for the showers I normally build. That’s it.

Reply

Donna

We have the entire shower area done with backerboard along with the curb Would it be okay to seal the backerboard with redguard then put down the pitched mud floor then seal up that floor?

Reply

Roger

Hi Donna,

Maybe, but why. It’s not needed and COULD cause issues. Overbuilding is not always the best option. :D

Reply

byron

while I am laying the tile, my unmodified thin set thickens and becomes difficult to work with. Is there a trick or can you remix unmodified thin set while laying tile.

Reply

Roger

Hi Byron,

You can make less, not mix so fast (that makes it set up quicker), allow it to slake (google it) while mixing, and yes, you can remix as many times as you want as long as you don’t add more water or powder to it.

Reply

Jeff

For a wood floor, can/should you use bricks for the curb or not? I’ve read so many different opinions on that. Some say that you should never use 2×4’s as they will rot if it leaks, etc. This is my first time tackling a shower floor, so please forgive my noob-ness. Thanks in advance!

Reply

Roger

Hi Jeff,

On wood use wood. The only reason to use bricks is because wood directly on concrete will pull moisture into the wood from the concrete and cause it to warp, swell, etc. If it leaks the material on your curb will be the least of your worries, the framing around the shower is the main concern. Just build it so it won’t leak. :D

Reply

Taylor

I’m attempting to build a tiled shower. I had to demo some concrete around my drain approx 4″ x 4″ in order to cut the pipe and get the three piece drain to an appropriate height. What I was wondering is if I can fill the hole in the concrete slab and pour the preslope at the same time? Or if I need to fill the hole let it dry and then preslope. I was thinking the first way would keep the concrete from moving.

Reply

Roger

Hi Taylor,

You can do it all at the same time.

Reply

Ginnette

We installed our preslope before we read your webite page and used only the Quickcrete sand and topping mix without the extra 30 lbs of sand per 60 lbs of the topping mix…are we going to have to redo the pre slope?? once it dried 24 hrs we attempting to vacuum of the small crumbles on top and some of the mud came up in a couple of areas, not deep, but there are viewable small pockets randomly spread out. Now that we have your website saved on our favorites, we will not get advice anywhere else and intend on adding the sand to the final layer of mud after we install the liner, but will that be possible if we did the pre slope without the added sand??

Reply

Roger

Hi Ginnette,

It should be fine on the preslope if it’s already done.

Reply

Luke

When installing the preslope on concrete, I presume the mud is installed while the thinset is still wet?…correct?

Reply

Roger

Hi Luke,

Correct.

Reply

Karrie

We are building a shower from scratch. Walls are open studs and the floor is joists, then subfloor, then backerboard. Should we build our curb & preslope before we hang the backerboards on the wall? I have looked everywhere & cannot find the answer to this. I apologize in advance if you have answered this somewhere. Thank you so much for this website!! It has help me tremendously! *Sidenote… we are using the Redgard method for waterproofing.

Reply

Roger

Hi Karrie,

You can do it either way. I normally do all the wall then build the curb butted up to them.

Reply

John

I am making my curb with brick pavers what product works best for adhering these to the concrete slab. Can you give a few names of products you like.

Reply

Roger

Hi John,

Thinset. Whatever thinset you’re using to install the tile will bond those bricks to the slab just fine.

Reply

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