How to Install a Hot Mop Shower Pan: Expert Step-by-Step Guide
- Isaac Ostrom
- Dec 28, 2025
- 11 min read
I’ve wanted to film a hot mop shower pan for a long time, because people ask about them nonstop. Homeowners hear the term “hot mop” and don’t really know what it is. Tile installers argue about it. Inspectors have opinions. And then there’s the reality: in a lot of places, hot mops are still the go-to method for building a shower pan that lasts.
So I finally made it happen. I brought in Bob from Bob Stanley Shower Pans, and here’s the cool part: these guys are the original hot mop company. If you’ve heard of a hot mop shower pan, it’s because crews like this have been doing it since the late 1960s. That’s not marketing fluff, that’s decades of pans that either leaked or didn’t leak, and the method survived because it works. You can hear us talking about that right at the start of the video.
In this post, I’m going to walk you through what we filmed, in plain English, with the details that actually matter. I’ll point out the stuff that makes a hot mop pan succeed, and the stuff that makes it fail. And I’ll call out a couple misconceptions that I see constantly, especially around pre-slope and weep holes.
If you’re a homeowner, this will help you understand what you’re paying for and what to look for. If you’re a tile contractor, this will help you talk intelligently about hot mop pans, even if you don’t personally install them.
Key Takeaways for Homeowners & Pros [TLDR Version]
Here’s the quick version before we get into the weeds.
First, a hot mop shower pan is a waterproof membrane made from hot tar (asphalt) and layers of roofing felt. It’s built right on site.
Second, the pre-slope matters. If you don’t create slope under the pan, water sits and stagnates. Bob stresses this in the video, and I’m right there with him. You can see the pre-slope board and the conversation about it around 00:04:44.
Third, drain prep is not optional. The drain has ports and weep paths that need to function. Bob explains how they used to drill those ports, and why grinding them open is easier and more effective around 00:03:37.
Fourth, weep holes are misunderstood. The hot mop process can fill weep holes with tar, and the job during hot mop is to mark and protect them, not to “clear” them on the spot. Bob says it plainly around 00:14:53.
Fifth, the “box layer” concept matters. They build up extra reinforcement layers at the floor and corners, then continue layering to hit the minimum thickness. Minimum three layers is standard, and they call it out around 00:13:39 and again at the end around 00:24:22.
Sixth, weather changes everything. Cooler weather makes tar thicker and easier to build up, so they can get the same thickness with fewer passes up the wall. Bob explains that difference around 00:16:57.
Tools Required (What’s Actually on the Truck)
If you’re a homeowner, you’re probably not doing this yourself. But it helps to know what a legit crew shows up with.
Hot mop crew tools and materials:Hot tar kettle (or tar rig), roofing felt (Bob mentions 15-pound felt), mops and spreading tools, torch for touch-ups, utility knives, roofing nails (used for some drain-port work), paper plugs for the drain, tape for protecting the flange and paper, and slope materials (tapered edge or cant strip, often called slope board).
Tile side tools you still need after the hot mop:Mortar bed tools, mixing gear, level and straightedges, drain protection, and whatever waterproofing and detailing you’re doing on the walls depending on your system. The hot mop pan is the pan, it’s not the entire shower build.
Now let’s talk about what’s happening, step by step.
What Is a Hot Mop Shower Pan, Really?
A hot mop shower pan is basically a site-built waterproof liner made from alternating layers of hot tar and roofing felt. The crew heats tar until it’s workable, then mops it on and embeds felt into it, then repeats until they hit the thickness and coverage they want.
This is old-school, and I mean that as a compliment. Old-school methods that are still around usually have one thing going for them: they work when they’re done right.
And Bob’s company is the kind of outfit that’s done it enough times that they have a rhythm. Watching a good hot mop crew is like watching a good mud man. It’s not flashy, but you can tell they know what matters and what doesn’t.
Step One: Understanding the Drain (Because the Drain Is the Whole Game)
If you don’t understand how the drain works, you’ll never fully understand why pre-slope and weep protection matters.
In the video, we’re looking at the drain parts and Bob shows how water travels through the channels under the drain assembly. You can see that discussion around 00:02:14. The basic idea is that water that gets into the mortar bed needs a path to the weep system. If those paths are blocked, you’re building a shower that holds water in the floor.
Then Bob talks about the ports. Early on, they used to drill them out. Now they grind them open, and he literally says it’s just as easy and more effective. That’s around 00:03:37, and it matters because those openings are part of making sure drainage happens the way it’s supposed to.
If you’re a homeowner reading this, here’s the takeaway: you can have the best tile in the world, but if the shower pan drainage design is compromised, the shower is going to smell, stain, or fail over time.
Step Two: The Pre-Slope (This Is Where Most Problems Start)
Let’s just get this out of the way. A flat shower pan is not a shower pan. It’s a bird bath.
The hot mop liner is not magic. It doesn’t make water disappear. It’s there to contain water and direct it toward the drain system. But if what’s under the liner is flat, water sits. That water can stagnate, it can discolor grout, it can contribute to odors, and it can stress the system.
Bob shows what they use for most standard showers: a roofing product called tapered edge or cant strip. They call it slope board. They cut it in, and they double it up so it creates a pre-slope to the drain. That whole explanation starts around 00:03:37 and rolls into the pre-slope emphasis around 00:04:44.
He also mentions that this slope board covers a huge percentage of standard stalls, but if you’ve got a bigger shower, you may need a different approach because the board can’t accommodate every footprint. That’s the part most people miss. They think “pre-slope” is a universal one-size-fits-all thing. It’s not. The shower size, drain location, and required pitch all matter.
And then Bob talks about what the board is made of, which surprised a lot of people: recycled paper fibers and perlite. It has that cellulose fiber texture. That’s around 00:04:44 to 00:06:26.
My opinion as a tile contractor: I don’t care if your pre-slope is made from slope board, deck mud, or unicorn dust. I care that it’s correct and consistent and actually pitches to the drain.
Step Three: Hot Tar and Felt Layers (The Part Everyone Thinks Is the Whole Thing)
Once the pre-slope is in, now the hot mop crew gets to do what they do.
The concept is simple: tar, felt, tar, felt, tar, felt. Every layer needs to be saturated and bonded. You don’t want dry spots, you don’t want air pockets, you don’t want a loose flap. Bob explains that they’re building everything so it’s fully saturated and continuous. You can see that layering process getting underway around 00:06:26.
This is also where I want homeowners to understand something about “cheap” shower bids.
If a crew is rushing, skipping layers, not going high enough on the walls, or not reinforcing corners properly, you might not see the problem immediately. But you’re basically gambling your remodel against time.
A shower pan failure isn’t a fun repair. It’s a tear-out. It’s dust. It’s money. It’s usually “why does my shower smell weird?” for a year before anyone admits there’s a bigger issue.
The Drain Plug Detail (And Why It’s Smarter Than It Looks)
One of my favorite little details in the video is the paper plug.
During the layering process, Bob leaves a plug in the drain area. The point is to prevent tar from getting where it shouldn’t and to protect the weep system during the work. You can see that idea pop up around 00:06:26 and later when they talk about leaving the plug in certain drains around 00:13:39.
This is the kind of detail that separates “a guy who can slap tar down” from “a crew that builds pans for a living.”
Step Four: The Box Layer (Corners, Floor, and Why Reinforcement Matters)
Hot mop pans fail in predictable places. Corners. Transitions. That floor-to-wall change of plane. Anywhere movement, stress, or poor workmanship stacks up.
That’s why Bob describes what they call the box layer. Around 00:13:39 he explains it as a back box and foot box concept, with two layers in key areas, then more on top of that. This is where you’re building durability into the pan.
Then he says something that matters for both homeowners and contractors: their showers will always have a minimum of three layers. Minimum. That’s not “if we feel like it.” That’s their baseline.
At the end of the video, he calls out the finished pan: three layers, 15-pound roofing felt, tar in between, nice pre-slope, weep protection, positive flow of water. That’s around 00:24:22.
If you’re a homeowner, that’s the language you should be listening for. When a contractor can explain layers, corners, pre-slope, and weep strategy without sounding like they’re guessing, you’re in a better spot.
Step Five: The Weep Hole Misconception (This Is Huge)
I want to slow down here because this trips up even experienced people.
Bob says it straight up: the tar does fill up your weep holes. And their job is to mark the weep hole, not clear the weep hole. He calls it a common misconception. That’s around 00:14:53.
What does that mean in real life?
It means the hot mop crew isn’t finishing the entire shower. They’re building the pan liner system, and then the tile installer still has work to do to make sure the drainage details are correct in the final assembly.
You don’t want random guys jamming screwdrivers into weep areas while tar is hot, “trying to clear it.” You want the system understood as a system, and you want the right person doing the right part at the right time.
Bob even mentions talking to the tile guy to make sure those weep holes are clear and free after the fact. That is exactly how it should be.
If you’re building showers for a living and you’re not coordinating this, you’re taking on risk you don’t need.
Step Six: Protecting the Drain Flange (Because Damage Here Is a Dumb Way to Lose)
Another detail I loved is the drain flange protection.
After they grind the ports and open things up, they tape the flange up. Bob explains why: you don’t want the paper exposed, and you don’t want someone coming by later and ripping something that causes a leak path. That’s around 00:16:15.
This is boring stuff. This is also the stuff that prevents callbacks.
Weather Matters More Than People Think
Bob gives a great explanation about temperature and how it affects the process.
On cooler days, tar stays thick and manageable. He likes that because it lets him build thickness without doing a million passes. He specifically mentions that in hot weather, like a 110-degree day in Sacramento, the material gets too fluid and you need multiple thinner layers to build up thickness. In cooler weather, he can get away with going up the walls twice versus six times for the same thickness. That’s around 00:16:57.
This is why I always tell people: jobsite conditions matter. The internet loves to pretend every install happens in a perfect laboratory. Real installs don’t.
If you’re a homeowner scheduling a remodel, you’re not going to plan your whole project around tar viscosity. But you should understand that crews who do this all the time are paying attention to temperature, material behavior, and build thickness in a way that a “once in a while” crew might not.
What a Finished Hot Mop Pan Should Look Like
At the end, we’ve got a finished pan. The big points Bob calls out are the same things I’d put on a checklist.
Pre-slope is present and correct.
Multiple layers are present, with a stated minimum of three.Fifteen-pound felt with tar in between.
Corners and changes of plane are reinforced.Weep protection is accounted for.
Positive flow of water is the goal. Anything that gets into the system should have a path to the drain and weeps. That’s around 00:24:22.
If you’re a homeowner, here’s a simple way to think about it.
You’re not buying tar.You’re buying a system that manages water correctly.
Where Hot Mop Fits in 2026 Showers (My Take)
I’m not here to argue hot mop versus modern sheet membranes like it’s a sports team.
I use modern systems all the time, and I like them. I also respect hot mop when it’s done by specialists who do it every day.
Hot mop has proven longevity, especially in regions where crews have the skill and local building culture supports it. It’s also a method that has been stress-tested in the real world for decades.
The downside is you need the right crew, and you need coordination with the tile installer so the whole shower build, especially the drain and weep strategy, is handled correctly.
If you’re a homeowner and you’re deciding between systems, my advice is simple.
Pick the system your installer is actually good at.Then make sure the details that matter are handled: slope, corners, transitions, drain, and weeps.
The “brand” of waterproofing matters less than the workmanship.
If you want help sorting that out for your specific remodel, this is exactly the kind of stuff people post in the Tile Coach Forum. You’ll get real answers from pros who have seen the failures and know what to look for.
FAQ Section
Q. What is a hot mop shower pan?
A hot mop shower pan is a site-built waterproof liner made from hot tar and layers of roofing felt. The crew mops hot tar onto the pre-sloped base, embeds felt, and repeats layers to create a thick waterproof membrane.
Q. Why is a pre-slope required under a hot mop pan?
Because water needs to move toward the drain. Without pre-slope, water can sit in the pan area and create long-term issues. In the video, Bob stresses the importance of pre-slope and shows the slope board they use for most standard showers around 00:04:44.
Q. What is “slope board” or “cant strip” in a hot mop shower?
It’s a tapered roofing product used to create the pre-slope toward the drain. Bob calls it tapered edge or cant strip and explains they double it up and cut it to fit most shower stalls.
Q. How many layers are in a proper hot mop shower pan?
Bob’s crew builds pans with a minimum of three layers, and the finished pan in the video is called out as three layers of 15-pound roofing felt with tar layers in between around 00:24:22.
Q. What is the “box layer” in hot mopping?
It’s the reinforced layering strategy at the floor and corners. Bob explains the box layer concept around 00:13:39, describing multiple layers in key areas before additional layers go on top.
Q. Do hot mop pans clog the weep holes?
Tar can fill weep holes during the hot mop process. Bob explains that their job is to mark and protect the weep holes, not clear them during mopping, and then coordinate with the tile installer to ensure the weep paths function. That misconception is addressed around 00:14:53.
Q. Does weather affect hot mopping?
Yes. Cooler weather can make tar thicker and easier to build up, reducing the number of passes needed to achieve thickness. Bob talks about the difference between a cool day and a 110-degree day in Sacramento around 00:16:57.
Q. Is a hot mop shower pan still a good method today?
It can be, especially when installed by experienced crews and coordinated properly with the tile installer for the full shower system. It’s been used successfully for decades, and Bob’s company has been doing it since the late 1960s.
Final Thoughts
I love filming stuff like this because it shows the reality behind the words people throw around.
Hot mop isn’t mysterious. It’s not magic. It’s craftsmanship and repetition, done by crews who understand water management and build thickness where it matters.
If you’re a homeowner, the best thing you can do is ask smarter questions. Ask about pre-slope. Ask how they protect weeps. Ask how many layers they do. Ask how high they go up the walls. If your contractor can’t answer that without stumbling, that’s your sign.
If you’re a contractor, don’t treat the pan like a separate planet. Coordinate with the hot mop crew. Make sure the drain and weep plan is clear. Protect the work. And don’t let simple details like a damaged flange or missed slope turn into a callback that ruins your profit.
If you want more nuts-and-bolts breakdowns like this, get into the Tile Coach Forum. I’m always trying to bridge the gap between what the industry actually does and what homeowners think is happening behind the scenes.
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