How to Install a Shower Pan Liner: Expert Step-by-Step Guide
- Isaac Ostrom
- 4 days ago
- 7 min read
What’s up everybody, Isaac here — your Tile Coach. Today we’re going old school. I’m showing you exactly how I install a traditional shower pan liner the way we used to do it before foam pans and liquid membranes became the norm.
Now, I’ll be honest — this method takes more time, more patience, and a solid understanding of how water actually moves under tile. But when you do it right, this thing will last decades.
I’ll walk you through my entire process: from building the curb and prepping the subfloor, to mixing the pre-slope, cutting and folding the liner, sealing the corners, and getting everything locked in tight around the drain.
So grab your coffee, a notepad, and maybe a trowel — because we’re diving deep into the craft.
Key Takeaways for Homeowners & Pros [TLDR Version]
The pan liner is your waterproofing layer — not the mortar bed or tile.
Always install a pre-slope under the liner so water flows toward the drain weep holes.
Keep weep holes clean — blocked holes cause water to back up and rot the subfloor.
Never puncture the liner within 2" above the curb height.
Use “hospital folds” at corners — never cut where the curb meets the wall.
Seal the drain flange with MS polymer or X-15 liner adhesive.
Use pre-formed dam corners for code-approved waterproofing at the curb ends.
If you’re a DIYer — consider modern alternatives like foam shower pans or liquid-applied membranes for easier installs.
Tools & Materials You’ll Need
OSB or plywood subfloor
2x4 lumber for curb framing
Tar paper or roofing felt (optional moisture barrier under mortar)
Fast-setting mortar mix (Rapid Set or similar) for pre-slope
Type S mortar mix (optional if not rushing the job)
PVC or CPE pan liner (4-, 5-, or 6-foot width rolls)
X-15 liner adhesive or MS polymer sealant
Pre-formed dam corners for curb junctions
Two-part drain assembly (with weep holes)
Staple gun with galvanized staples
Utility knife & scissors
Trowel and margin trowel
Level or straightedge
Step 1: Preparing the Subfloor and Curb
Before you touch the liner, get your foundation solid.
In this project, I’ve got an OSB subfloor and a 2x4 curb built right into the shower base. The builder left the dent shield (a moisture barrier) on the walls — we’ll float those later in a future video.
First, I roll out a layer of tar paper over the OSB. This isn’t for waterproofing — it’s just a slip sheet to keep the mortar from bonding to the subfloor and to prevent the plywood from sucking moisture out of the mix too fast. Bonus: when someone tears this shower out in 100 years, it’ll come up easier.
Step 2: Creating the Pre-Slope
This is one of the most overlooked steps in shower building, but it’s absolutely critical.
The pre-slope ensures that any water getting under your tile (and into the mortar bed) actually flows to the drain instead of pooling and creating a swamp underneath your tile.
I mix up Rapid Set mortar mix — it’s fast, sets in about 15 minutes, and lets me keep moving the same day. You can absolutely use Type S mortar instead if you want more working time; just plan to let it cure overnight.
Using the bottom 2x4 of the curb as a reference, I set my slope at about halfway up that board — roughly ¾ inch higher than the drain at the perimeter. That gives me a nice even fall from all sides.
Spread the mud evenly, using a straightedge to screed from the walls toward the drain. Don’t worry about perfection here — this isn’t your tile bed. You’re just giving the liner a consistent slope to rest on.
Pro tip: Keep blue tape over the drain bolt holes so you don’t pack mud into them. (Ask me how I learned that one…)
Step 3: Installing the Drain and Sealant
Once your pre-slope sets up enough to walk on (about 15–20 minutes with Rapid Set), it’s time to prep the drain.
I thread the drain bolts back into the flange before applying sealant. This helps “tent” the liner slightly and prevents it from sliding around when you center it later.
For sealant, I’m using MS polymer — it’s cheap, sticky, and bonds PVC to metal or ABS perfectly.
Apply two full rings of sealant: one on the inside of the flange and one on the outside. This double bead ensures water can’t back up underneath the liner if the drain ever clogs.
Step 4: Measuring, Cutting & Positioning the Pan Liner
Time to roll out the liner. Most home centers carry 4- and 5-foot-wide rolls — I used 5-foot material here because my shower is 48" x 60". Always go wider than you think; you want the liner to run 6 inches up the walls on all sides.
Center the liner over the drain, making sure you’ve got enough to fold up each wall and completely wrap the curb.
Now form what I call “hospital folds” — tuck the liner on itself at the corners so you get clean 90° turns without cutting. You should never slice through the liner at the wall-to-curb transitions.
Once it’s in place, I add a few temporary staples right at the top edge — just enough to hold it. Never staple below 2 inches above the finished curb height. That’s code and for good reason — any puncture below that line risks a leak.
Step 5: Cutting the Drain Holes
With the liner centered and stapled, feel for the drain bolts underneath.
Use your utility knife to make tiny X-shaped cuts right over each bolt. The goal is to stretch the liner over the bolts snugly, not leave giant holes.
Once all the bolts poke through, gently cut out the drain opening itself. You should see the sealant squeeze up around the edge — that’s how you know you’ve got a watertight bond between the liner and the flange.
Reinstall your top flange and tighten the bolts back down.
Step 6: Folding and Sealing the Corners
Now we tackle the most misunderstood part — the dam corners.
This is where a lot of installs fail because people either skip these corners or they cut them wrong.
If you just fold the liner up and leave the top of the curb unprotected, water can sneak right behind your tile and rot the framing.
I use pre-formed PVC dam corners and X-15 liner adhesive to bond them.
Here’s how I do it:
Cut a small relief notch in the liner to wrap neatly over the curb without stretching.
Apply X-15 adhesive to both surfaces — the liner and the pre-formed corner.
Let it tack up for about a minute, then press them together tight.
Smooth it out so there are no wrinkles or air bubbles.
Fold the liner neatly over and staple only at the very top, well above the curb.
Repeat this on both sides of the curb.
You’ll end up with clean, code-approved waterproof corners that’ll outlast the shower itself.
Step 7: Final Adjustments and Checks
Take a few minutes to inspect everything:
The liner should rise at least 6 inches up each wall.
The corners should be folded — not cut — except where the dam corner overlaps.
There should be no fasteners below 2 inches above the curb.
The drain bolts should be tight and sealed.
Weep holes clear and unobstructed.
Once you’ve verified all that, you’re good to go. This is now a proper old-school pan liner install — tight, sloped, sealed, and ready for your final mortar bed.
Common Mistakes to Avoid
Skipping the pre-slope. That’s how you get moldy, stagnant water under your tile.
Nailing through the liner on the curb. Instant failure. Don’t do it.
Blocking the weep holes. Always double-check that those stay clear.
Cutting the liner at corners. Always fold, never slice.
Using the wrong adhesive. Regular PVC glue won’t bond pan liners — use X-15 or MS polymer sealant.
Rushing the mortar cure. If you use Type S, give it overnight to harden before installing the liner.
For DIYers: Easier Alternatives
If this all sounds like a lot — that’s because it is. Traditional pan liners take practice to master.
If you’re new to tile work or just want something simpler, consider:
Pre-sloped foam pans (like Schluter or GoBoard systems)
Liquid-applied waterproofing membranes (like RedGard or HydroBan)
Both are more forgiving and easier for beginners, especially if you’re not floating your own mortar beds.
Frequently Asked Questions (FAQ)
Q: Why is the pre-slope necessary?
A: Without it, water just sits under the liner. The pre-slope ensures it drains through the weep holes instead of pooling and growing mold.
Q: Can I screw or nail the liner to the curb?
A: No way. That defeats the whole purpose. Only staple or fasten above 2 inches higher than the curb.
Q: What kind of sealant should I use at the drain flange?
A: Use a polymer-based sealant like Rapid Set MS Polymer or the approved X-15 liner adhesive.
Q: How do I keep the weep holes from clogging?
A: Cover them during mortar work and make sure the top of the drain assembly stays clean when you pack the final mud bed.
Q: What if my liner isn’t wide enough for the shower?
A: You can seam two pieces together using X-15 liner adhesive. Overlap by several inches and roll the seam flat.
Q: How long should I wait before doing the final mud bed?
A: If you used Rapid Set for the pre-slope, you can move on the same day. If you used Type S, let it cure overnight.
Final Thoughts
There you have it — an old-school pan liner install done right.
It’s not the easiest waterproofing method out there, but it’s tried, true, and bulletproof when done correctly.
I’ve been setting tile for over 20 years, and this method still has its place. But I’ll also say — if you’re new to the trade, don’t be afraid to try modern systems too. The key is understanding the why behind each step, not just following instructions blindly.
And if you’re diving deeper into DIY or pro-level tile work, join the Tile Coach Forum or subscribe to my channel — we’re always sharing tips, tricks, and real-world lessons from the job site.
Thanks for joining me on this one — I love being your Tile Coach. Until next time, keep your corners tight, your weep holes clear, and your waterproofing bulletproof.
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