I’m sure you already know that the hardest part of building a custom shower is laying the concrete floor. It’s also know as the shower pan or shower base. You may have heard talk of a pre-slope or seen people wrestling with big sheets of black plastic/vinyl/rubber on TV. You probably think it’s impossible to get just the right angle so the water flows into the drain. Or maybe you’re deathly afraid you won’t do it right and water will leak everywhere. Hell, lots of professionals are intimidated by concrete shower pans. My neighborhood plumber did his own shower pan and told me you couldn’t pay him to install one for someone else. Wow, I must be crazy for trying it myself!
Nope. It really wasn’t that bad. And I am not an expert, a contractor, or even a handy (wo)man. I have never remodeled a full bathroom before. I have never built a shower pan. I am just like you! Well, maybe a little gutsier 😉 With this method there is no pre-slope, black liner, or liquid waterproofing to roll on.
There are several different methods to build a shower pan, but I decided to go with a mortar bed and Schluter Kerdi waterproofing membrane. But you already knew that from the last post where I build the shower curb. There are 3 more components to my shower pan: the drain, the concrete (mud) base, and the waterproofing membrane (Kerdi). We’ll talk about the first 2 today. I recommend watching this video, which explains the entire process, as an overview before getting into specifics.
This is my video showing the whole mudding process.
Schluter Systems has a ton of other videos for various installation situations, which is good because chances are your situation is not exactly the same as mine. I think this is a huge reason home owners don’t try things themselves — you might find a great tutorial but it doesn’t apply to you exactly. You can use this tool on the Schluter website to make a customized video series for your specific situation. Cool!
- Concrete subfloor with a big hole around the drain pipe – so apparently I needed this video on Concrete Box Out Drain Preparation (who knew?!)
- No access to the plumbing from below (it’s a concrete slab), so I watched this video
- I watched this video long before I tiled, so I would know what to expect
Always check local building codes and get all permits and inspections necessary for your project.
Installing a Schluter Kerdi-Drain
I. Concrete Drain Box Out
A drain box out just means that I needed to make the hole in my floor smaller, leaving only enough room for the drain assembly. This will give me a solid surface to lay my deck mud.
1. Cut the riser pipe to the correct height first. (The riser pipe is the black pipe sticking out of the ground, that I will attach the drain to.) Test fit the Kerdi-drain assembly to verify the correct height. It is definitely easier to cut the drain pipe before you build the box out, trust me I learned this the hard way when I had to trim it again later.
2. Use 4″ pipe coupler to act as a protective barrier between the mortar and space around the riser pipe. If the coupler is the correct height, lay it in place and check that it’s level. If it is too short, begin to fill hole with mortar or concrete to bring the hole (and the coupler) up to the right height. My hole was very deep and needed to be filled, so when I finished tiling the bathroom floor I added the leftover thinset to the hole. This is what the pipe coupler looks like.
3. Fill the hole with thinset mortar, deck mud, concrete, whatever you have on hand. I used more left over mortar from my floor tile installation. It’s not pretty, but it’s effective
4. If you’re not installing the drain right away (because you like to work on 15 projects at once) then protect the opening by filling it with something like plastic shopping bags or rags.
II. Attach the Kerdi-Drain
1. Verify the fit. Mine needed tweaking, so I shaved off a small portion of the coupler to make it the drain sit perfectly level. You can see where I trimmed it in the labeled picture above.
2. Remove all dirt from the riser pipe and drain.
3. Check the manufacturer’s directions for your adhesive and apply it accordingly. My riser pipe is made of ABS, so I purchased an ABS Kerdi-Drain, and had to use ABS cement. You DO NOT use primer with ABS cement. The hardest part for me was opening the damn can. It was sealed shut (maybe used and returned?) and in a panic to get it open before my deck mud dried, I opened the Oatey can with a can opener. That meant I had to throw the rest out, but you do what you’ve got to do.
4. Twist and lower the drain assembly over the riser pipe and make sure it’s level.
*If you’re really curious what steps 3 and 4 look like, or you don’t really believe that I do this stuff myself, then you can check out this terrible quality video, taken by my 7-year-old, just don’t come complaining to me when you feel nauseous.*
5. Support the bonding flange (wide, white part of the drain assembly) by filling in the area underneath with loose mortar. You can use the same deck mud you’re going to use for the shower pan, just add more water. I jumped right into the mortar bed next…
Building a Mortar Shower Bed
I. How to Make Deck Mud
Deck mud (also know as dry pack mortar, floor mud, or screed) has 3 ingredients; sand, portland cement (not masonry cement), and water. People use various proportions of the 3 ingredients to get the perfect deck mud and you can check out the John Bridge website for more info. He recommends using a 5:1 ratio of sand to portland cement. I ended up using a 4:1 ratio, but I did buy a 5th bag of sand just in case, I just didn’t use it. First mix the dry ingredients, then slowly add water and mix until the mortar is dampened completely. I mixed mine in a wheel barrow because I was too cheap to spend $13 on a concrete mixing tub. The wheel barrow worked just fine, but I did make only half a batch at a time. I also used a shovel, but a garden hoe would have been better. FYI – I left the wheel barrow outside and carried the mud into the bathroom one bucket at a time.
Deck mud should be damp enough to hold itself together, but doesn’t have any excess water. The lack of water is what makes deck mud easier to work with, building the shower pan is like building a sandcastle, and the set time is longer. The lower water content also keeps the mortar from shrinking as it cures, and shrinkage is not what we want for our shower pan. Here’s a 2-minute video of me mixing deck mud.
II. How to Calculate Proper Slope
Like we already discussed, the main thing people worry about when building a concrete shower pan is getting the slope right. Obviously you need water to flow toward the drain, not away from it, so the rule of thumb is to have at least 1/8 inch of rise for every foot of run. Huh? Just figure out which corner is furthest from the drain and measure the distance. This tells you your “feet” measurement (the run). Now calculate the rise by multiplying the by 1/8″.
Ex: If it is 3 feet from the center of the drain to the furthest corner, then your minimum rise is 3/8″, but you’d be safer if you went even higher.
Now that you’ve determined rise, you must add it to the height of the shower drain to get the final height.
Ex. Your drain sits 1″ off the ground. Use your level to mark the height of the drain on the wall. Don’t just measure up 1″ along the wall because your floor may not be level, which means your 1″ mark won’t be the same height as the drain. Now that you have the drain height marked, add the rise and make a second mark. It is this second mark that determines the final height of the shower bed.
III. Let’s Build this Shower Pan Already
1. Mark the perimeter height of the mortar bed. Schluter doesn’t say to do this, but I made a line on all 3 walls, and the inside of the curb, indicating the final height. (This is the Schluter video)
2. Mix the deck mud. (see above)
3. Start along the perimeter and build a mortar screed (a wall of deck mud). Tamp and level it using the handy line you drew in step 1. Here is the beginning of my perimeter screed.
4. Pour the deck mud (dry packed mortar) into the shower and spread it with a trowel. (The stuff in the bucket above is the loose mortar I mixed up to use under the bonding flange, not dry pack mortar.) Tamp it down and slope it from the perimeter toward the drain. You already took all your measurements, so just play with the deck mud until it’s smooth and nicely sloped. If the perimeter is always the highest point and the drain always the lowest you don’t have to worry about the rest.
Here it is almost finished, then completely finished.
5. Wipe any mud off the drain. And everywhere else for that matter.
6. Allow the concrete to cure overnight. The moment of truth — checking that the perimeter is level and everything is sloping toward the drain. Woohoo! We’re all good!
It took me 1 hr 17 min to get from step 3 to step 5, but I did a lot of fiddling around with it. I thought it was over 3 hours until I was able to recover the video I took of the whole process. For months I thought it was lost forever, my computer was showing it was a corrupted file. Well… thank goodness, I was able to get it back and now you can enjoy that 77 minutes for yourself, sped up to 16-32x speed of course!
Did you know you can pin videos to Pinterest too?! Go for it! Or use this.
Next step is to add the Kerdi waterproofing membrane!
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