How to Create a Shower Floor – Part 4

by Roger

Well, you’ve made it to the final step. If you have arrived at this portion of the instructions without first reading the rest, start with How to Create a Shower Floor. Go ahead, I’ll be right here when you get back. I’ll just sit back and drink this beer Pepsi while I wait.

Okay, now that we’ve ensured that your shower liner is indeed waterproof and won’t leak into your dining room and carve the Grand Canyon into your basement we’re ready for the final portion. The top mud bed is the surface onto which your shower floor tile is actually installed.

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. Since you have a pre-slope beneath your liner (umm, you DO have a pre-slope beneath your liner, right?) you already have the correct slope for drainage. By making a consistent mudbed for your top slope it will follow the slope for the same amount. Know what I mean?

Here, take a look at this badly created diagram and that may help explain it – and don’t give me any crap about my lack of photoshop skills! You can click on the diagram for the full-size version.

diagram of a shower floor

The top mud bed is what we have left for your shower provided you’ve followed in order. See how the top mud bed is properly sloped toward the drain even though it is a consistent thickness? That’s what I mean.

A couple of notes before we start making a mess. You can install your moisture barrier and backerboard on the walls at this point if you want to. DO NOT put any screws through the liner, stop them above the top of the liner. The top mud bed will hold the bottom in place if you choose to do it like this. Your moisture barrier must go over the top of your pan liner as in the diagram. This ensures that any moisture will run down into the shower rather than into your framing behind your wall.

In my wonderful diagram I have the wall substrate or backerboard installed after the top mud bed is fabricated, you can also do it in this manner. Installing it before, though, assists in getting a level perimeter around the base of your shower since you can draw lines on the wall. It’s up to you.

Determining the thickness of your top mud bed relies mostly upon the amount of vertical movement you have in your drain. You need to make sure that you can unscrew the center portion (this moves the top of the drain up) enough to be level or a hair below the top of your mudbed with tile. The easiest way to determine this is to start at 1 1/4″ – that’s just the thickness I prefer to have if possible.

Location of Weep holes in shower drain

Location of Weep holes in shower drain

Weep holes in drain covered with pea gravel

You need to place pea gravel, spacers, or something similar around the drain where the weep holes are located. This prevents deck mud from clogging up your weep holes and nullifying all of your hard work. If plugged up the shower cannot properly drain beneath your floor tile and your house will fall down and your dog will burst into flames. Okay, maybe your house won’t collapse, but it won’t be a good thing. Make sure you place something there that prevents clogging of your weep holes.

Place a piece of your floor tile on the base of the drain – on the upper part of the flange – and unscrew the barrel of the drain until you reach 1 1/4 inch. As long as the barrel is still firmly screwed into the flange at this height you have enough to create a 1 1/4″ top mud bed. If the drain falls out before you reach 1 1/4″ (it won’t) – go with 1″.

Measuring drain for top mud slope

Marking line for top mud bed slope

Now the fun part – we’re gonna make your lines so you can see what your doing, where you need to be, and make your slope correct and consistent. Get your 2 x 4 (which is actually 3 1/2″ x 1 1/2″ – economy I guess) and set it on top of your drain (Figure 1). Measure from the liner to the top of the 2 x 4. In this photo it is (or close enough to) 4 3/4″.

You then need to make that mark at the same height all the way around the perimeter of your shower walls (figure 2). If you have installed your backerboard you can just make that mark on the wall at a height of 4 3/4″. I use a laser because I’m a big Star Wars fan and that’s how I roll. Get one, they’re great for building showers and annoying small animals. That’s a versatile tool right there!

This may look a bit confusing at first, the 2 x 4 and all, but it will make sense shortly. Or not . . .

Now we need to prepare some more deck mud. Get out your shovel and mixing box. If you need the recipe again it’s here: How to Make Deck Mud. Start with the perimeter of the shower and dump your mud in there. I always start along the back wall of the shower.

Creating a level perimeter a shower floor

Creating a level perimeter a shower floor

Creating a level perimeter a shower floor

Get a good amount of deck mud packed along the walls higher than where you want it to be. Once you have a good amount packed against the wall grab your 2 x 4 and place it flat against the wall. Get your hammer and beat the deck mud down with the 2 x 4 until the top of the 2 x 4 is level with the line you’ve made on the wall or your laser line (figures 3, 4, and 5).

Simply continue to do this around the entire outside perimeter of your shower keeping all the edges level with your line. By utilizing the 2 x 4 with the laser or the drawn line you can be certain that the floor is level all the way around (Figure 6).

Some people have asked me why I have a hole in one of my 2 x 4’s. It’s a very detailed explanation – ready, pay attention – so I can hang it on a nail when I’m not using it. :D That’s all, stop overthinking everything, it’s a hole in a 2 x 4. You don’t need a hole in your 2 x 4 unless you have a storage problem.

Ensuring a Level Perimeter
Figure 6

In the next post we’ll finish up your floor, fill in the center and get ready for tile!

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Hi Roger. Great info and detail and i love your humor. In figure 6 there is no picture of pea gravel. I assume you will add it before finishing the mud to the drain? I noticed that you are using two different drains/examples in your pics as one is black and one white but you only show the pea gravel in first figure.



Hi Tina,

Yes, there is pea gravel around both of them in the finished product. I often have pictures of different projects in one post, I rarely take time to document every step as I’m doing it – I’d never get done. :D So I tend to combine photos in order to have examples of everything I’m trying to explain.



Thank you. You not only know what you’re talking about and have experience and informative illustrations to back that up( which is a Rarity, knowledge that is) but I enjoy your humor immensely. Thank you again.



HI I recently installed a pre pitch for a shower over a concrete surface and have noticed hollow sounds when tapped on it.Is this due to lack of bonding of the mud to concrete and should I be concerned with this or once the liner and top mud bed go over it it will be ok.I used blended mason mix.
Thanks Griff



Hi Griff,

Unbonded mud beds will sound hollow. But I don’t know if it’ll be a problem or not – I have no idea what ingredients are in blended mason mix.



Just a tip that I found. Your local pet store should carry aquarium rocks. These were perfect; nice and small. It came in a small bag so I dont have a bunch of extra rocks laying around.



Hi Roger,

Enjoy and appreciate your site. Before unscrewing the barrel, do really need to place a piece of tile on the flange? Seems like your photo clearly shows what you mean by a 1-1/4″ thick top mud bed…and it doesn’t include a piece of tile.




Hi Nick,

You don’t need to, just ensure you either get the correct height or you leave the barrel loose enough that it can be unscrewed to the proper height after the mud cures.


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