How to Create a Shower Floor – Part 3

by Roger

Well now we’re ready to waterproof your curb. If you have reached this post before reading the previous two, start with How to build a shower floor from the beginning.  Now that you’re ready to get the curb cut and waterproofed lets get it done.

And yes, I know my pictures suck – I’m a tile guy for cryin’ out loud, not a professional photographer. Until you try to balance a liner, a razor knife, a margin trowel, and a camera while trying to take a photo don’t give me any crap about it. Oh, and you can click on any of the images for a full-size version – partake in the full glory of how much my photography sucks.

We need to start by finding the inside lower corner of your shower pan and making certain that the liner is pressed firmly against it. Then follow it up the corner of the curb and wall to the top inside corner of your curb. This is the spot at which you will start the cut in your liner.

Cutting a liner for a curb when shower walls will be backerboard

Cutting a liner for a curb when shower walls will be backerboard Click to Enlarge

Deciding in which direction to make your cut depends upon how you plan to waterproof the walls. If you are simply using a cementious backerboard on your walls with a moisture barrier behind it you want to cut from that point straight up. Or, more precisely, cut your liner so that when it is placed flat against the studs the cut will go straight up from that point.

If, however, you are using a topical waterproofing membrane (that’s just fancy-ass, pinkie in the air talk for waterproofing that goes right behind the tile) I cut it a bit differently. Start from the inside top corner of the curb and cut straight out to the outside corner of the curb.

Cutting a liner for curb when using a topical membrane

Cutting a liner for curb when using a topical membrane

The reason for this is simple – to me anyway – if you are using a cement backerboard or any type of substrate where moisture will get behind your wall, you want to have as much of a liner at the ends of the curbs as possible to run up the wall. With a topical membrane such as Schluter Kerdi or a liquid such as Redgard you don’t have to worry about that. By the time any water behind the tile gets to the bottom of your waterproofing it should be well below your curb – provided you’ve installed it correctly.

On the inside corner of the curb you should install a ‘dam corner’. These are pre-formed outside corners which are glued to the liner to cover the spot where you’ve made the cut. I do not have a picture of these because I don’t use them, I’m a hypocritical bastard like that. But you should. (Use the dam corners, not be a hypocritical bastard.)

When you do glue your dam corners in you need to make sure you use the correct type of glue. Just like drain pipes – pvc glue for pvc liners and cpe glue for cpe liners. The glue WILL NOT work the other way around. Really, don’t try it, it’s an expensive lesson. Take my word for it.

The liner gets wrapped over the top of the curb

The liner gets wrapped over the top of the curb

Now that you have the ends of the curb cut we need to move on to preparing the curb for tile. Take your 2 x 4 that you used to level your pre-slope perimeter (you did that, right?) and place it in the inside corner of your liner against the curb and the floor. This ensures that the liner lies completely against the floor and the curb without air pockets or empty space beneath it. Then nail the OUTSIDE of your liner to the curb – only the outside, never the inside.

Please note: these photos were taken after my final mud bed was in place. I installed the curb last on this particular project. You can do it before or after your final mud bed is fabricated. Dealer’s choice.

Nailed only on the outside of the curb

Nailed only on the outside of the curb

To hold the liner in place over the top of the curb you need some metal lathe. Provided your curb consists of three 2 x 4’s your lathe needs to be cut into strips sized to fit over your curb from the floor on the outside to the inside bottom corner of your shower. Bend the lathe into a ‘U’ shape (length-wise) and place it over the top of your liner over your curb. Something else I do not have a photo of. Just because I’ve never taken one, not because I do it differently.

You only need to nail the liner on the outside if you have a wooden curb. If your shower is on a concrete subfloor you used bricks for your curb – right? Pay attention, if you fail the quiz later you owe me a beer Pepsi.

I have one more photo for this post and this is it. Isn’t that spectacular? It’s just to show you how I do the ends of the curb when using Kerdi on the walls. “But why don’t you use Kerdi on the floor too?” Glad you asked. It’s a very technical answer and requires you pay attention to every part of it or you may get lost in all the details. Ready? Because some people don’t wanna pay over 100 dollars for a shower drain. Whaddya gonna do?

Shower pan liner on the end of the curb.

Shower pan liner on the end of the curb.

Couple of things I’d like to point out about that last photo before you go bustin’ my chops too hard. First, the excess liner is not yet cut out. I cut it straight down the edge of the drywall there and everything gets tucked straight back into the wall. Secondly, yes, I put a nail through the liner. A foot above the curb. You can light it on fire that high if you choose to do so. (I wouldn’t recommend that, though. And no, I don’t want to talk type about it.)

Now we have to water test your pan to make sure it does not leak. Note: most cities and counties REQUIRE this to be done – don’t skip it. The test simply ensures that all your hard work is indeed correct and your pan does not leak. That’s it.

You need to plug the drain (or you’ll be there all night trying to get enough water into it) which you can do with either a $75 specialty plug, or a water balloon. You pick. You need to make absolutely sure that (and I’m assuming you chose the balloon option) the balloon is pushed far enough down into the drain to block the weep holes as well.  If they are not it will let you know that your weep holes work correctly. Unfortunately it does nothing to reassure you about the liner. If you look carefully into the drain you should be able to see the holes for the weep holes, get below them with your plug.

Then just fill ‘er up. All the way up to just a hair below the top of the curb. (take the 2 x 4 out of it first if it’s still in there) and leave it set for 24 hours. After the 24 hours have elapsed and you are reasonably recovered from your recently induced hangover, check to make sure the level of the water has not gone down. If it hasn’t you are ready to go.

Now if we could just get that elf guy off his ass to write the next post you will learn how to fabricate your final mud bed and tile that sucker. Hang tight, we’ll go get him. Check back real soon, y’all. And as always, if you have any questions at all please feel free to use the comment section below.

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Stephanie Maps

Custom Building Products aka redgard tech support 800-272-8786 says “nothing” will bond/seal between redgard and polypropylene liner.

They recommend either furring the concrete wall, installing backerboard putting the polypropylene liner behind the backboard doing away with the need for redgard entirely.


Painting Redgard on to the concrete wall, on the outer surface of the backboards and onto the surface of the preslope. Requiring much more redgard but doing away with the need for the polypropylene liner entirely.

I don’t want to lose the inches in the shower to fur it and i am not eager to use/trust ONLY redgard as a pan liner.




Redgard works just fine as a pan liner. When done correctly it works just as well as any other. Really. :D



Are the dam corners made of different materials? In other words if I have a CPE liner do I need CPE corners?



Hi Freiheit,

Yes, you need to get the same material your liner is made of.


Stephanie Maps

Thank you SO much for this site Roger. Tis’ truly awesome!

i know how to handle a wood stud wall.. i know how to handle concrete wall but what should i do since i have BOTH?

I’ve got a brick curb on a concrete floor with wood studs with the fancy notch cut out on on two shower walls and a solid concrete wall on the third shower wall. I’m ready to create a pre-slope but have realized i don’t really know exactly how i’m going to handle the waterproofing/sealing where polypropylene shower floor liner meets the Redi-gard on the concrete wall.

Meaning – if the polypropylene liners lays on top of the pre-slope and 6 inches up the studs in those notches that works great if ALL my walls are wood studs. But since one of my walls are concrete i was going to Redi-gard that entire wall.

So i am thinking after pre-slope. FIRST Redi-gard the entire concrete wall from the top of the shower all the way down until i am maybe 4 inches above the pre-slope. THEN lay down the polypropylene liner in floor and 6 inches up the walls. The liner will lay inside the notches of the studs but on top of the last 2 inches of Redi-gard on the concrete wall. How do i – should i seal the polypropylene liner to the Redi-gard there?

Or am i COMPLETELY off base with my entire approach? Am i going to create a bulge in the tile near the bottom of the concrete wall if i attempt this?

Maybe i should do away with the polypropylene liner entirely and JUST do 3 coats of the Redi-gard on the entire concrete wall, 6inches up the wood studs and the entire final mud shower floor (before tile).

i dunno. i’m largely clues-less but thanks to your site am slowly getting there.
What would the floor elf do?

thank you muchly,



Hi Stephanie,

I assume you mean redgard, not redi-guard. You have two options:

1. You can frame out a small wall in front of the concrete wall and build as a regular traditonally lined floor with the liner behind the backer.

2. You can use a topical membrane (redgard does work) as the waterproofing on your floor and walls.

You can not make a transition from a traditionally waterproofed shower floor to a topically waterproofed concrete wall.


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