How to Build a Shower Pan
How to Build a Shower: Shower Pan Installation
This is the second article of the How To Build A Shower series:
- How To Build a Shower Article 1 – Shower framing and plumbing
- How To Build a Shower Article 2 – Shower pan installation
- How To Build a Shower Article 3 – Shower tile installation
In the first article, we covered the initial steps of building a shower — shower framing and shower plumbing.
In this second article, we will walk through the process of building a traditional shower pan using concrete mortar (a.k.a. deck mud).
What is a Mortar Shower Pan?
A mortar shower pan (or mud shower pan) is a hand-built shower base constructed from concrete. Once finished, the shower pan forms the drain containing floor of the shower. Shower pans are typically sloped to a central drain and finished with a tile surface. The purpose of a finished shower pan is to create a stable shower floor that quickly empties waste shower water through its drain.
While most shower water drains in this fashion through the primary drain, some does not. The finished surface of many showers is not perfectly waterproof. Some water will penetrate the surface of the shower and pass into the core of the shower pan. Grouted tile surfaces are water resistant, but will, especially over time, allow some water to pass through. This leads us to the secondary job of the shower pan.
The secondary job of a shower pan is to re-direct any water that has penetrated the surface of the shower floor back into the drain. A properly built shower pan redirects water back to the drain by way of an embedded waterproof membrane that is sloped toward and sealed to the drain. This system forces penetrated water back to and into the drain, through special weep holes built into the side of shower drains.
Shower pans built without a shower liner, or similar system of waterproofing, can allow water to pass readily through the shower pan into the floor and wall structures. The concrete used to build shower pans is readily permeable to water and will easily allow water to pass through it into surrounding building structures without the installation of a shower liner.
Why Go Old School with a Shower Pan?
There are many ready-made shower pan systems available to use when building a shower. Even so, it is hard to beat a traditional hand-made mortar shower pan.
Pre-made shower pans offer speed and ease of installation, but often lack the rigidity, strength and flexibility of a hand-poured concrete pan. Packaged systems (Kerdi, others) get expensive and complicated without offering compelling advantages over hand made shower pans.
How Do You Build a Mortar Shower Pan? Its All About the Layers…
A hand built shower pan is built in layers around a shower drain assembly.
Shower Pan Layers in Steps:
- Frame shower walls, curb and add wall blocking to create shower base “box”
- Install shower drain assembly (if not already installed)
- Cover shower base with builders felt (tar paper)
- Pour first mortar base layer (sloped from walls and curb to drain base)
- Install waterproof shower liner over first mortar layer sealed and clamped to drain
- Pour top mortar over shower liner (sloped from walls and curb to drain)
- Tile finish the top mortar layer
Building a mortar shower pan is a relatively simple task of assembling these layers. It will take a bit of time and some work, but the reward will be a long lasting, durable shower base.
Before you begin building your new shower, you should have a stable sub-floor and the appropriate shower drain in place. Once construction of the shower base is complete, you will need to finish the shower pan surface with tile or a suitable surface.
More information regarding the prep and finish work of the shower pan can be found in the other shower construction articles;
- How To Build a Shower Article 1 – Shower framing and plumbing
- How To Build a Shower Article 3 – Shower tile installation
If you are ready to build your own shower pan, read on. Prior to starting on the build, you should have a properly framed and plumbed shower rough-in (covered in the first article of this series). If all of this is in place, get your tools and materials ready to build a shower pan…
How to Build a Shower Pan – Overview
- Level: Intermediate
- Time: Days
- Shower Pan cost: $100
- Total Shower cost: $300 – $1000 +
How to Build a Shower Pan – Project Big Picture
- Block-in shower pan “box”
- Install layer of tar paper
- Install metal mesh reinforcement
- Pour and slope concrete base layer
- Install shower liner
- Assemble shower drain
- Pour and slope concrete top layer
- Finish surface with tile
Materials – Shower Pan and Drain Assembly
Tools and Supplies – Shower Pan and Drain Assembly
|Item||What I used||Cost|
|Galvanized Staples||$8 / box|
|Shower liner adhesive||$15|
How to Build a Mortar Shower Pan – Step by Step
- Confirm rigidity of the subfloor and proper drain base installation.
Prior to building a mortar shower pan, you should have an stable, flat, sufficiently-strong subfloor with an appropriate 2″ drain installed (see Build a Shower Series – Part 1: Shower Framing and Plumbing).
- Frame the shower curb.
If you are planning on a shower curb, you have several options. You can build a form to pour mortar into or use materials to form the core of the curb and apply mortar on top of this core.
I used the core and mortar around method using several stacked 2x4s to create the curb core.
To build a curb using a 2 x 4 core, stack and fasten several (I used 3) 2x4s sequentially to the subflooring. First screw the bottom 2 x 4 to the subfloor, and then screw the second 2 x 4 to the fastened first 2 x 4 and repeat to desired curb height.
To build a curb using forms for a concrete pour, assemble forms using boards or similar and fill the forms with concrete.
- Cover shower pan plywood with a layer of asphalt felt (tar paper) or similar.
To begin the shower pan construction, add a layer of roofing felt (tar paper) to the bottom of the shower pan.
The felt will serve as a moisture barrier for the first layer of mud helping the mortar to retain moisture while curing. It will also help to isolate the subfloor from the shower pan.
To install the asphalt felt, cover the flat surface of the subfloor, cutting around the drain base. Add a few galvanized staples to secure the felt to the plywood.
- Add blocking to create shower pan box.
Next, add wood blocking between the wall framing to create a “box” for the shower pan.
For the blocking material, use pieces of 2x6s, plywood or similar material — I used pieces of the 3/4″ plywood I used to build my subfloor. The blocking should be at least as high as the shower curb.
- Mount galvanized wire mesh to base of shower pan and over curb.
Add galvanized mesh or stucco wire to the bottom of the shower pan, The mesh will reinforce base floor mud layer of mortar and help hold the mortar to the shower curb.
Bend the mesh slightly to create “waves” in mesh to help embed the mesh in the center of the floor mud. Carry the mesh around the curb framing and secure with galvanized staples.
- Prepare floor mix.
Traditional floor mix mortar (floor mud or deck mud) is a 5 to 1 mixture of sand and Portland cement. To make strong, stable mud, add just enough water to create a thick clay-like mixture that just holds its shape when packed.
A latex concrete admixture can be added for some or all of the water component of the mortar mix to add flexibility and strength – in many cases, however, latex is overkill for typical shower pan mortar.
That said, I did substitute about half of the water requirement for my mix with latex admixture (I like overkill).
To make quality mud, first dry mix the ingredients (even if from a premixed bagged product) thoroughly with a hoe to ensure proper sand / cement contact.
Once mixed, add water (or a water/latex blend). Use only enough water to create a mix that will hold its shape when squeezed in your hand, but not release excess water.
Dry mixes create strong, stable concrete with less shrinkage and higher compression strength.
- Build the shower pan first layer with floor mix mortar.
Using the prepared floor mix mortar, build the first layer of the shower pan. Slope this base layer from the walls of the shower toward the shower drain at a drop of 1/4 to 3/8″ per foot.
To help you create the proper slope, first determine and mark the shower walls with the proper starting height for the mortar. This starting height is the mortar height at the wall that will provide the proper slope toward the drain.
The amount of added height needed at the wall can be calculated by the adding to total calculated added height needed for the desired slope. Most shower pans require a minimum of 1/4 to 3/8″ of drop per foot.
To figure the necessary height at the shower wall to obtain this slope, measure the distance from the wall to the drain edge and multiply by the desired slope (1/4″ to 3/8″ per foot).
Distance from the drain to the wall: 2 feet
Desired slope: 1/4″ per foot
Result: 2 feet x 1/4″ per foot = 1/2″ extra height at the wall.
In this example, the mortar level at the shower wall will be 1/2″ higher than the height of the mortar surface a the drain edge.
Because the distance from the shower walls to the drain varies for nearly every shower pan (the exception being a round shower pan with a centered drain), the amount of slope throughout the pan will vary as well.
To set the minimum proper slope for the entire pan, calculate and mark the wall height for the wall location that is the furthest from the drain. The point is typically the corner that is the furthest from the drain.
Once you determine and mark this starting wall height, use a level to continue this line around the entire shower. This line will be starting height of the mortar bed at the walls of the shower to provide the proper minimum slope for the entire pan and provide a level boarder for the entire pan.
Now with the wall mortar level marked on the shower walls, dump mortar mix into the shower box and build the first layer of the shower pan.
Add mud starting at the rear of the shower pan. Use a straight edge or similar to screed the mud from the wall mark to the edge of the drain base and continue adding mud until the entire pan is formed.
Next, use mud to build the first mortar layer of the shower curb. Add mortar to all sides of the curb, using the curb mounted stucco wire to help hold the mortar to the lumber curb core.
Add a thick enough layer of mortar to cover the stucco wire wrapped studs. You may find the use of several short straight boards (2x4s or similar) or long magnesium floats helpful when forming the mortar curb. Slope the top surface of the curb slightly toward the shower pan to provide a drainage path toward the shower pan.
Once all the mortar is applied and sloped to the shower pan and curb, finish the mortar surface smooth with a steel trowel and allow to dry overnight.
- Install shower liner over the cured mortar first layer of the shower pan.
With the first layer of mortar built and cured, next install the shower line on top of the mortar base layer and preliminary curb layer.
The shower liner creates a waterproof barrier that contains and redirects any passed water into the shower drain. It is essential to slope this initial base toward the shower drain to allow proper drainage of water on top of the shower liner into the drain. Shower lined installed directly on the subfloor or on a flat mortar base will hold stagnant water with will eventually lead to leaks, mold and failure of the shower pan.
A properly installed and sloped shower liner will allow water that has penetrated the shower floor to quickly move to the drain and empty into the drain through small weep holes in the side of the drain.
To begin installing the shower liner, lay a continuous sheet of the liner over the cured shower base wrapping it over the top of the shower curb. Smooth the liner flat to determine the proper size of the liner. Be sure to thoroughly flatten the line along the surface and corners of the pan and shower curb. Liners installed without sufficient slack can stretch and fail.
Prior to laying the shower liner on the shower pan, clean the cured mortar surface of the pan to remove any potential abrasive debris that could damage the shower liner.
In addition to cleaning the shower pan base, some will add a layer of roofing felt (tar paper) over the mortar shower base to help protect the liner from abrasion of the mortar base.
To determine the proper size of the shower liner prior to cutting it, lay the liner in the shower pan smoothing it into the corners and over the curb as described above. Plan to carry the liner up the walls of the shower 8 – 12″ or higher and at least slightly higher than the shower curb.
The liner should be one continuous piece, covering the entire pan, up the walls and over the curb. The line will serve as your waterproof barrier. Think of it as a pool liner that will need to hold the entire volume of water contained with the pan up to the shower curb. Do don’t leave it too short when running it up the shower walls and don’t cut or penetrate the liner within this “pool” area.
Once you are satisfied with the position and lay of the liner, use a marker to mark the desired cuts on the liner. Do not cut the shower line at the corners or as it passes over the curb. Instead, fold the liner at corners (similar to wrapping a gift) and tuck them into the wall cavity at corners.
If you must cut the liner at the curb or for complex corners, use commercially available patch kits with the proper liner adhesive to cover the cuts.
To accommodate the thickness of the shower liner against the lower walls of the shower, some will shave some material from the face of the lower portion of the shower studs. This step can help ensure the to be installed backer board will lay flat over the area were the shower liner passes up the shower walls.
With the liner marked, remove the liner from the shower and cut the liner using a scissors or similar. Then, place the liner back into the shower to confirm the proper size and fit. Next, smooth the liner over the shower pan and into the corners. Fold the corners and tuck the fold toward the wall cavity or against corner studs if present. Secure the top of the liner and top of the folds with roofing nails or exterior grade screws only the the very top edges of the wall portion of the liner. You may also use liner adhesive or silicone caulk applied to the field of the shower pan for added stability.
It is essential that you do not penetrate the liner below the level of the shower curb as accumulated water can pass through fastener penetrations leading to leaks.
Then, secure the liner to the to the shower curb using liner adhesive or silicone caulk applied to the shower side and top of the mortar curb. Do not use nails, staples or other penetrating fasteners on the shower side or top of the curb if possible. The top of the shower curb should provide a continuous, waterproof path back to the shower pan and shower drain. Holes made by fasteners along this path will compromise this barrier.
To finish the shower liner over the curb, trim the liner at the front top edge (as I did – see above photo) or fold it over the top edge to the front face of the curb if you may benefit from waterproofing the front face of the curb (if you do not plan to install a shower door or glass for instance).
- Install the Drain Clamp **Important step**
Once the shower liner is installed, cut the liner and clamp to the shower drain.
With the shower liner installed, the shower drain base will be under the shower liner. Smooth the liner over the drain base to determine its location. Once located, cut small holes for the four shower drain bolts.
To locate the bolt heads, push down on the liner with your fingers. Once located, make a very small slit just above the bolts heads just big enough to allow the bolt heads to push through the liner.
Next, cut the drain hole in the liner. Locate the drain hole by pushing down on the liner. Feel the edges of the opening and using a sharp knife, carefully cut out the liner to match the inside of drain hole.
Once the bolt heads and drain holes are cut, seal the underside of the liner to the drain base using silicone sealant or liner adhesive. Do not use sealant on the topside of the liner as it may block water drainage from the liner into the drain.
Finish the drain installation by installing the top drain assembly.
Install the top of the drain (the drain collar clamp) by sliding the collar over the bolts, twisting clockwise to lock the collar on to the bolts and finally tightening the bolts. The tightened assembly will compress and seal the liner to the drain.
Use care when tightening clamp bolts. Move bolt to bolt tightening each bolt a little at a time.
With the drain clamp assembled, insert the drain riser (drain throat) and adjust the riser height to correspond to desired top mortar layer thickness. Most drain risers are threaded to allow height changes by rotating the riser.
Remember to consider tile thickness when adjusting drain riser height. The finished tile surface should match the drain grate height in the finish shower floor.
Prior to pouring the top mortar layer, pile gravel, tile spacers or similar over the weep holes of the drain collar to help keep the weep holes open and functional after the mortar is poured.
At this point, your shower liner and drain assembly should form a waterproof basin.
To test the liner and drain assembly, plug the inside of the shower drain and flood the shower pan. The pan should hold the fill level of water over an extended period of time (overnight, for example).
- Install lower course of tile backer board.
To create the proper layering of the shower walls over the shower liner, install the lower course of your tile backer board at this point. In this way, the tile backer board of the shower will create a water path down the wall into the shower pan above the liner. Install the lower portion of the tile backer board now also adds stability to the shower walls as they will be embedded in the top mortar layer of the shower pan.
When installing the backer board to incorporate the bottom edge in the shower pan, you only need to install the lower pieces of the backer board as this time. Once the shower pan is finished, you can then install the remaining backer board.
Install the backer board over the shower liner with the bottom edge of the backer board gaped 1/2 – 1″ above the shower liner covered shower pan base. Scrap pieces of plywood or smooth backer board work well as spacers to position the backer board prior to securing. Avoid using rough, cement board as a spacer on top of the liner that could damage the shower liner.
Spacing the lower edge of the backer board will help prevent mechanical damage to the liner by the bottom edge of the backer board and help prevent movement of water up the shower wall. Gap the backer board above the shower curb as well.
With the backer board in place and properly gaped above the liner and curb, fasten the backer board using the appropriate backer board screws only at a level well above the shower liner and curb. Fasteners placed in the lower portion of the backer board will penetrate the underlying shower liner and lead to leaks. Remember that the lower portion of the backer will be incorporated into the top mortar layer of the shower pan and be quite secure.
- Add the top layer of floor mix mortar.
With the backer board in place and secure, the pan is ready for the top layer of mortar. This top and final mortar layer of the shower is poured directly on top of the shower liner. The top layer will serve as the weight bearing structural layer and form the sloped surface which tile will be installed on.
Plan to build this top layer 2 – 3″ thick with a 1/4″ to 3/8″ per foot slope to the drain. When creating the slope for this top layer it is often not necessary to add much additional slope as you will be building on top of the previously sloped base mortar layer.
While planning the thickness of the top mortar layer, adjust the height of the drain throat to allow for the desired mortar thickness with consideration for the final thickness of the tile and thin set to be installed. The final height of the tiled shower pan should just match the top edge of the shower drain and account for the desired thickness of your planned tile.
Prior to pouring this layer, protect the weep holes of the drain assembly by covering with pea gravel, marble chips or tile spacers to prevent blockage of the weep holes by the floor mix.
This top layer of mortar should have sufficient thickness for mechanical integrity and sloped as mentioned above. In general, the mortar should be at least 1 1/2 – 2″ thick at the drain. Plan for and set this thickness at the drain by adjusting the drain collar to the correct height. If you remove the top drain grate, the level of mortar at the drain will be just below or close to flush with the drain collar (dark gray round thread piece in photo above)
Once the drain height is set, use a straight edge to mark the proper mortar height at the shower walls (which now will be your installed tile backer board). This mark should again correspond to a 1/4 – 3/8″ slope toward the drain with a mortar thickness of at lease 2″.
With the drain set and walls marked, dump damp floor mix onto the shower liner and screed smooth using wooden or magnesium float. Again, work from the back of the shower to the front. Dump the mud directly on the shower liner and screed with a level piece of 2×4, magnesium float or similar.
Once the mud is in place and at the proper slope and thickness, smooth and finish the surface with a steel trowel or similar.
Next, add the top layer of mud to the shower curb, similar to the pan, directly on top of the shower liner. You can reinforce the curb mud layer by embedding an “L” shaped piece of wire mesh into this second mud layer. Use care not to penetrate or damage the shower liner with the wire mesh or tools while building this top layer of the curb.
Finally, finish the top surface of the curb with a steel trowel or similar tool. Allow the completed shower pan to cure for a day or two prior to tiling.
- NEXT: Tile your shower. See “Build a Shower – Part 3:Tiling a Shower”