This is the second article in our Building a Shower series and in it we will walk through the process of building a custom shower pan using the traditional technique of a sloped mortar base with a sandwiched vinyl shower liner.
Before you begin building the shower pan, you should have framed shower walls and subfloor with drain plumbing and supply plumbing in place – both of which are covered in our first article How to Build a Shower: Framing and Plumbing.
Shower Pan for Tile: What it is and how to Build One
A shower pan is the sloped base of a walk-in shower that forms the shower floor. The shower pan usually is built around a specialized floor drain which is sealed to the waterproof layer of the shower pan.
Traditional shower pans where built using dry-pack mortar (concrete) with an embedded waterproof membrane or layer that is sealed to a specialized shower drain that allows water to drain into the main drain opening as well as side weep holes.
The finished shower pan forms the slight-sloped floor of the shower and is often finished with a tile surface. A shower pan is traditionally constructed in two layers with an embedded water-proof membrane or layer in the middle.
This middle layer serves the special purpose of redirecting any shower wastewater that has passed through the surface of the shower floor back into the drain.
The Shower Pan Serves Two Primary Functions
- To quickly direct shower wastewater into the shower drain by way of a sloped-to-the-drain surface.
- To redirect any water that has passed through the shower floor and contained by the water-proof shower liner, back into the side weep holes of the shower drain.
While the sloped surface of a typical shower pan handles a majority of shower wastewater, proper functioning of the water-proof middle barrier or shower liner (#2 above), is crucial for a properly functioning, dry, mold-free, leak-proof shower build. Mortar is water resistant but readily water permeable. Because of this, some water will find it’s way through the shower floor and if this passed water is not stopped, will result in a leaky shower.
So Why Build a Traditional Mortar Shower Pan?
Although there are many ready-made shower pan systems available, it’s hard to beat a traditional hand-made mortar shower pan. Hand-built mortar shower pans are inexpensive, long-lasting and, if done right, reliable and leak-free for decades.
While off-the-shelf pre-made shower pans offer speed and ease of installation, they often lack the rigidity, strength and flexibility of a hand-poured mortar pan. Packaged systems (Kerdi, others) get expensive and complicated without offering compelling advantages over hand made shower pans. But, hand-made mortar shower pans do require a bit of patience and work.
How Do You Build a Mortar Shower Pan? Its All About the Layers…
A hand made shower pan is built in layers around a shower drain assembly.
Shower Pan Layers in Steps:
- Frame the shower walls, install subfloor and shower curb
- Add wall blocking to create shower pan “box”
- Install the shower drain assembly through shower subfloor
- Cover shower subfloor with asphalt saturated felt (tar paper)
- Place the first mortar base layer, sloped from walls and curb to drain base
- Install the shower liner and seal and clamp to the shower drain
- Install tile backer board on shower walls gapped above shower liner
- Place the top mortar layer over the shower liner, sloped from walls and curb to drain
- Finish the top mortar layer – typically with tile
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, leak-free, durable shower base.
Start With A Strong, Stable Base
A new shower built with a mortar shower pan, concrete backer board and tile is heavy. Before you begin, ensure that you have adequate sub-flooring, framing and appropriate shower drain plumbing in place. 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…
OVERVIEW | Build a shower Pan
SUPPLIES LIST | Build a shower Pan
- Asphalt Felt 15# TARCO STD15 36x144#15 Much cheaper to purchase locally because of shipping costs.
- PVC Shower Liner Cement HH-66 PVC Vinyl Cement Glue Do not use PVC pipe cement!
- Shower Bed Guide Goof Proof Shower STE-201 and EXT-202 kits Pre-Pitch guide for first mortar layer and Quick-Pitch guide for top mortar layer
- Shower Bed and Curb Guides Goof Proof SSK-401 kit pre-pitch, quick-pitch and Kirb-perfect kits
TOOLS LIST | Build a shower Pan
STEPS | Build a shower Pan
- Prepare subfloor and drain plumbing.
Prior to placing mortar for your shower pan build, your subfloor should be flat and suitably strong. I used 3/4″ plywood over reinforce floor joists. You will need to install the lower portion of the shower drain assembly installed (see How to Build a Shower: Framing and Plumbing for shower drain install details)
- Frame the shower curb.
If building a shower curb, you have two main options:
- Use lumber (stacked 2x4s or 2x6s) or blocks as a curb core.
- Use forms to pour a concrete curb.
I used option #1, using 3 stacked 2x4s to form a curb. To do the same, stack and fasten several (I used 3) 2x4s sequentially to the subfloor. 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.
Then fasten metal mesh to the lumber curb to help hold mortar to it, which will be applied with the first mortar layer. You may also skip attaching mesh and a first layer of mortar to the curb lumber and simply wrap the shower liner directly over the 2 x 4s, skipping the bottom mortar layer on the curb and just applying a top, final, mortar layer on top of the shower liner.
- Form the shower pan box frame with blocking between the studs.
Create the shower pan “box” form by installing blocking between wall framing members. Use framing pieces or sheathing material as blocking. I used scraps of the leftover 3/4″ subfloor plywood. The blocking should be at least as high as the shower curb.
- Prepare shower pan for the first mortar layer.
Prepare the bottom of the should pan box for the first mortar layer by installing a layer of asphalt felt over the subfloor plywood. This felt layer 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. Install the asphalt felt to cover the entire bottom surface of the shower pan, cutting an opening for the drain. Secure with several staples.
Over the asphalt felt, install a layer of mortar reinforcement mesh. Use galvanized hardware cloth (metal mesh) or a plastic or synthetic reinforcement mesh. If using a metal mesh, bend to create slight waves in the material to improve embedding of the mesh within the mortar layer. If using metal mesh, use care to avoid sharp edges above the mortar layer that could damage the to-be-installed shower liner which will lay above the first reinforced mortar layer.
If using a slope guide system like the Goof Proof Pre-Pitch (STD-201) guide, you would typically not use a reinforcement mesh.
- Mix and place the first mortar layer.
Traditional floor mix mortar (floor mud, deck mud or dry-pack mortar), which is used to build mortar shower pans, is a 4 – 5 to 1 mixture of sand and Portland cement plus water. When making floor mix mortar, add just enough water to hydrate the mix. Excess water will weaken the mortar. Limit the amount of water by adding just enough water to create a thick, clay-like mixture that just holds its shape when packed. Once packed, you should not be able to squeeze water out of the mix.
A latex concrete admixture can be added to the mortar mix to improve compressive strength, flexibility, durability and adhesion of the mortar mix. Follow the directions of the specific product you plan to use. Generally, latex admixtures are substituted for some of the water in the mix. For my mortar mix, I used a 50:50 mix of water and latex admixture to hydrate the mortar.
To make the mortar, begin by dry-mixing the mortar mix (even if from a premixed bagged product) thoroughly with a hoe to ensure proper sand and cement contact. Next, add water (or a water plus latex admixture blend) using only enough water to create a mix that will hold its shape when squeezed in your hand, but not release excess water. Drier mortar mixes create strong, stable concrete with less shrinkage and higher compression strength.
With the mortar mixed, place the first mortar layer. Slope the mortar bed with a 1/4″ – 3/8″ slope from the walls to the drain location. Prepare for the slope by marking the walls of your shower with a mortar level that will provide the desired slope to the drain. Calculate the amount of height needed at a wall by multiplying the distance to the wall from the drain in feet by 1/4″. For example, if the is 3 feet from the drain, the wall mortar level should start 3/4″ of an inch above the drain edge level. To draw wall mortar height guides around the shower, measure any point, add the amount of needed rise and use a level to continue that line around the perimeter of the shower.
You can also use a commercial slope guide (like the Goof Proof kits) to help easily create a uniform pitch mortar bed.
With your shower walls marked and/or a slope guide set up, place your mixed mortar into the shower pan and begin forming your base (“pre-slope”) mortar layer. Add mortar to the pan 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. If using a pitch guide, like the Goof Proof products, the tops of the plastic struts will form the top layer of the mortar bed and serve as screen guides while forming the mortar bed.
Next, add mortar to form the base mortar layer of the curb. If using 2 x 4s as I did, add mortar to the outside surface of the lumber with its’ attached wire mesh and smooth. If using forms, commercial or your own, fill them with mortar and tool smooth.
Allow the shower pan and curb mortar to cure at least overnight.
- Install the shower liner.
Next, install the shower liner over the base, sloped, mortar layer of the shower pan and the curb. The shower liner is waterproof and will provide a permanent, waterproof barrier for the shower pan that is sealed to the shower drain. It is very important that the shower liner is installed on a properly sloped mortar bed. Un-sloped shower liners will hold water and cause all sorts of moisture-related problems including mold growth. Do not install a shower liner on a flat subfloor or flat base mortar layer!
Installing the shower liner by first measuring and cutting it to the proper size.
Unfold and spread out the shower liner over the shower pan and around the shower curb. Allow the an additional 8 to 12″ of liner at the shower walls to allow you to carry the liner up the walls well above the level of the shower curb. Before cutting the lineer, be sure to thoroughly flatten the liner 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.
The liner should be one continuous piece, covering the entire pan, up the walls and over the curb. The liner is the waterproof barrier for the shower pan – 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 not 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.
Finally, 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).
- Seal the shower liner to the shower drain.
Shower drains are specialized drains with a clamp mechanism used to seal to shower liners. Shower drains also have weep holes in their sides, just above the liner clamp to allow weep water to re-enter the shower drain. This way, any water stopped by the shower liner will flow downhill along the shower liner and back into the shower drain.
To connect and seal the shower liner to the shower drain clamp, first cut out the portion of the drain liner that lies directly under the shower liner. In addition, make very small slits over the drain base bolts to allow the bolts to pass through the shower liner. Next, run a bead of silicone caulk or specialized shower liner sealant under the cut edge of the shower liner at the cutout for the shower drain. Now install the top drain clamp over the shower liner and tighten the mounting bolts to seal.
Once the shower drain clamp is in place, install the remaining drain riser piece into the drain throat. Most shower drains have thread on both the drain riser and drain throat to allow height adjustment of the drain level. Adjust this level to match your planned mortar thickness and tile thickness of the top shower pan mortar bed.
With the shower drain sealed to the shower liner, you should have a waterproof shower pan which can be flood tested once the sealant used under the liner clamp has cured.
- Install the shower wall tile backer board and place the top mortar bed.
Prior to placing the top mortar layer of the shower pan, install the tile backer board so that it will be embedded into the shower pan top mortar layer. Embedding the tile backer board into the top mortar layer provide structural stability of the shower walls and allows for proper water runoff from the shower walls onto the shower floor.
Install tile backer boards slightly gaped (1/2′ or so) above the shower liner surface. This gap will help prevent mechanical damage to the shower liner from any movement of the tile backer board over time. It will also help prevent capillary-action movement of water up and into the wall assembly. For the same reasons, gap the tile backer board above the shower curb as well.
When securing the lower portion of the backer board, use great care to avoid placing screws or nails through the bottom portion of the backer board that could penetrate the shower liner behind the backer board. When installing the backer board, you only need to install the lower course if you like and can install the upper portions after finishing with the shower pan.
With the lower portion of the tile backer board installed, mix and place the top mortar bed of the shower pan.
This top and final mortar layer of the shower is poured directly on top of the shower liner and will serve as the installation base for the floor tile.
Plan for 2″ – 3″ of mortar for this layer. Slope this top layer the same 1/4″ to 3/8″ per foot as the bottom mortar layer. This top layer of mortar should have sufficient thickness for mechanical integrity and in general, should be at least 1 1/2 – 2″ thick at the drain. Since you have already sloped the base mortar layer which you are placing this mortar layer on top of, this layer can be a uniform thickness, depending on the existing slope of the first 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. 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.
To ensure proper slope of this top mortar bed, mark the walls as you did for the first mortar layer using a level to determine the proper mortar levels at the walls of the shower.
Once the drain height is set and walls are 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 straight piece of 2×4 lumber, level, magnesium float or straight edge.
Once the mud is in place and at the proper slope and thickness, smooth and finish the surface with a steel finishing trowel.
Next, place the top layer of mud over the shower curb, similar to the shower 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 curb top surface of the a steel trowel.
You are now ready to finish the shower pan with tile. Before tiling, allow the completed shower pan and curb to cure for a day or two. See how to tile your shower here.