How to Lower a Concrete Floor for Shower Pan Installation
- Isaac Ostrom
- 5 days ago
- 10 min read
If you’ve ever tried to build a proper shower pan on a concrete slab without dropping the floor first, you already know how that story ends. You’re either fighting height the whole way, or you’re trying to cheat the slope, or you’re praying the drain magically lands where you need it. And none of those are a real plan.
When I’m doing a slab shower, I want control. I want the drain where it belongs. I want enough depth for a real mud bed. And I want the pitch to be right so the shower actually drains, doesn’t pond water, and doesn’t turn into a science experiment six months later.
So in this post, I’m going to walk you through exactly how I lower a concrete floor for a shower pan install. Marking, plunge cutting, chiseling, setting the drain, and floating the floor with the right slope. This is the kind of work that looks intimidating until you’ve done it once. Then you realize it’s just steps, the right tools, and not rushing the messy parts.
Key Takeaways for Homeowners & Pros [TLDR Version]
Lowering the slab gives you room for a proper mud bed and the correct slope to the drain.
I plunge cut the perimeter with a grinder first, then break out the middle with a rotary hammer.
Leave yourself a small “lip” at the edge to use as a reference when you’re checking depth and slope.
Plan your slope at 1/4 inch per foot minimum to the drain.
Dry-fit the drain and trap first. Don’t glue yourself into a corner.
Use a rubber coupler where it makes sense so you can fine-tune position.
Before mud, burn in a wet thinset slurry so the mud bonds to the slab.
Pack mud under the drain so it doesn’t move while you float.
Float the floor like you mean it: consistent pitch, clean transitions, no birdbaths.
Tools Required
Here’s what I consider the “don’t-show-up-without-it” list:
Angle grinder with a diamond blade (for plunge cutting the perimeter)
Rotary hammer with a chisel bit (for breaking out the slab)
Shop vac (you’re going to make dust and rubble, no way around it)
Dust mask or respirator (silica dust is no joke)
Fan or ventilation setup (helps keep the air moving)
Tape measure and marker
Level (2 foot and/or 4 foot)
Straightedge (long level, screed, or aluminum straightedge)
Rubber coupler (for connecting drain assembly to waste line when needed)
Thinset mortar (for slurry bond coat)
Deck mud / dry pack (for floating the pan)
Bucket, mixing paddle, margin trowel
Wood or magnesium float, steel trowel
Optional but helpful: spray bottle with water, knee pads, hearing protection
Why I Lower the Concrete in the First Place
Let’s get the “why” straight, because once you understand that, the rest of the job makes sense.
A shower floor has to slope to the drain. Industry minimum is 1/4 inch per foot. That’s not some fancy preference, it’s the baseline for water to actually move. If your slab is flat and you just try to build a pan on top of it without dropping anything, you run into a few problems:
You don’t have enough depth for the drain body and mud bed without making the shower floor sit way too high.
You end up cheating the slope because you’re trying to keep height down. That’s where puddles come from.
You don’t have clean transitions at the perimeter, especially if you’re tying into an existing bathroom slab and you don’t want a speed bump at the entry.
So lowering the concrete is basically me buying myself space. Space to set the drain correctly, space to float a real pan, and space to do it clean.
Plan the Shower Pan Like a Grown-Up (Before You Touch a Grinder)
This is where most people mess up: they start demo first and planning second.
Before I cut anything, I’m thinking through:
Where’s the drain going? Center? Linear? Offset?
What’s the distance from drain to farthest wall? That determines how much total drop I need.
How thick do I want my mud bed at the drain?
What’s my finished floor height outside the shower, and what’s my curb or curbless plan?
Quick slope math (this matters)
Minimum slope is 1/4 inch per foot. So if your farthest point is 4 feet from the drain, you need at least 1 inch of fall from perimeter to drain. If it’s 3 feet, you need at least 3/4 inch.
That number drives everything. It tells you how deep the recess needs to be and how much room you need to float.
Safety First (Because Concrete Dust Will Ruin Your Day)
Concrete work is dusty. Grinding and plunge cutting is especially dusty. And silica is not something you want hanging out in your lungs.
So here’s what I do every time:
Mask or respirator on. Not optional.
Fan blowing out a window if possible, or at least moving air away from me.
Shop vac running and cleanup as I go.
Eye protection and hearing protection. A grinder screaming in a small bathroom hits different.
If you’re a DIYer, this is where you don’t try to be tough. Suit up, then work.
Step 1: Mark the Area You’re Dropping
I start by marking the footprint of the shower floor area that needs to be lowered. Most of the time, I’m dropping the whole shower pan zone. Sometimes I’ll drop a slightly larger area if I want extra working space or I need room for plumbing adjustments.
Here’s the key: your perimeter line is your boundary. That line is what your plunge cuts follow, and those cuts are what keep your breakout controlled.
I’m not eyeballing this. I’m measuring and snapping lines if I need to. When you’re done, you want a recess that’s predictable, not a crater that looks like it got hit by lightning.
Step 2: Plunge Cut the Perimeter with a Grinder
This is where the grinder earns its keep.
I use a diamond blade and plunge cut along my markings. I’m basically creating a “break line” so when I start chiseling, the slab breaks where I want it to. This also keeps the surrounding slab from cracking out farther than planned.
Depth-wise, you’ll usually start around 1/2 inch and work deeper where you need it—often approaching 1 3/4 inches depending on the drain and mud thickness you’re building. Your exact depth depends on your drain setup and how much room you need for slope.
And here’s a pro tip that saves headaches:Leave a little lip at the perimeter.That lip becomes your reference point when you’re checking depth and slope later. It’s like giving yourself a built-in measuring ledge.
Step 3: Break Out the Concrete with a Rotary Hammer
Once the perimeter is cut, I switch to the rotary hammer with a chisel bit and start knocking out the interior.
This part is loud, dusty, and kind of satisfying if you’re into controlled destruction.
A few pointers I’ve learned the hard way:
Start near an edge and work inward. Don’t just attack the middle like you’re mad at it.
Break it into manageable chunks. You’re not trying to lift a 200-pound slab piece out of a bathroom.
Stay inside your perimeter cuts. Let the cuts do their job.
Most slabs are around 4 inches thick, so yes, you’re doing real work here. But if your perimeter cuts are good, the breakout goes way cleaner.
Step 4: Check Your Depth and Your “Shape”
Once you’ve got the concrete out, you’re going to have an uneven recess. That’s normal. You’re not done yet.
This is where that perimeter lip becomes gold.
I lay my level on the lip and check:
How deep am I at the drain zone?
Do I have enough room for my drain body and mud bed?
Do I have consistent depth to build my slope without making the perimeter too thin?
A good target depth that comes up a lot is around 1 1/4 inches minimum in the recess area, but again, it depends on the system and the drain. The point is: you want enough room to float a pan that doesn’t feel like it was built out of crumbs.
If you’re high in spots, chip more. If you’re low in spots, you can correct with mud later, but don’t use mud to fix a disaster. Use mud to refine a good base.
Step 5: Drain Placement and Dry-Fitting the Plumbing
Now we talk about the part that can make or break the whole shower: drain placement.
I set the drain and trap in the recess and dry-fit everything first. I want it centered (or wherever the plan says it goes), and I want it at the right elevation relative to my future mud bed.
A lot of the time, you’re connecting into an existing waste line. That’s where a rubber coupler is your friend, because it gives you a little flexibility for alignment and adjustment.
Here’s my rule:Don’t glue the drain until you’re 100 percent sure.
Once you glue it, you’re married. And the divorce is expensive.
So I check:
Is the drain level?
Is it sitting at the right height for the finished pan?
Is the trap aligned and not putting stress on the fittings?
Do I have the room to pack mud under it for support?
When that all looks right, then we can commit.
Step 6: Prep the Slab for Mud (Thinset Slurry)
This is one of those details that separates “it lasted a year” from “it lasted 20.”
Concrete and deck mud need a bond coat. So before I dump mud in the recess, I mix up a wet thinset slurry and spread it over the slab.
You’re basically painting the slab with thinset so the mud bed grabs and bonds instead of just sitting there like a loose sandcastle.
Don’t let it skin over. I spread slurry and place mud while it’s still wet and tacky.
Step 7: Support the Drain with Mud
If the drain moves while you’re floating, you’re going to hate your life.
So I stuff mud underneath the drain assembly to support it. I want the drain solid. No rocking, no settling, no “it’ll be fine.”
This is especially important because while you’re shaping the floor, you’re pushing, pulling, and packing mud. If the drain isn’t supported, it can shift without you noticing until it’s too late.
Step 8: Float the Shower Pan Floor (This Is Where the Magic Happens)
Floating is where the shower becomes a shower.
I’m building a smooth, consistent slope from perimeter to drain at 1/4 inch per foot minimum. I’m also making sure the surface is flat in the tile sense. Flat doesn’t mean level. Flat means no humps, no dips, no random birdbaths.
How I float it in real life
I establish my perimeter height first.
I pack mud around the perimeter to create a solid “screed” edge.
I pack and shape toward the drain, using my straightedge to connect perimeter to drain.
I check slope constantly with a level.
I refine the surface so it’s ready for waterproofing.
A shower pan should feel intentional. When you run a straightedge across it, it shouldn’t rock like a teeter-totter. When you put a level toward the drain, it should show consistent fall everywhere.
If you’re doing small tile, you can get away with a little more texture. If you’re doing big format tile on a shower floor, you better be on your game. Big tile shows everything.
Practical Tips That Save Time and Prevent Mistakes
Here’s the stuff I’d tell you on a jobsite, not the stuff people write in a perfect-world instruction manual.
Keep the perimeter clean. Ragged edges make waterproofing harder later.
Don’t over-chisel your boundary. Let the plunge cut be the stop line.
Vacuum constantly. Dust hides cracks and low spots.
Measure slope from the farthest point. If it slopes right there, it’ll usually slope right everywhere.
Don’t guess drain height. Dry fit, check, then commit.
If you’re unsure, stop and think. Concrete work punishes rushing.
FAQ Section
Q. How deep should I lower a concrete floor for a shower pan?
It depends on your drain assembly and how thick your mud bed needs to be, but a common target is roughly 1 1/4 inches minimum in the recessed area, with additional depth if needed to achieve proper slope. The goal is enough room for the drain and a sloped mud bed without raising the shower floor too high.
Q. What slope should a shower pan have?
Minimum recommended slope is 1/4 inch per foot toward the drain. This prevents standing water and helps the shower drain properly.
Q. Can I just grind the concrete down instead of breaking it out?
For small adjustments, grinding works. But for a full shower pan recess, breaking out concrete after perimeter plunge cuts is usually faster and more practical. Grinding that much concrete is dusty, slow, and rough on tools.
Q. Do I need a thinset slurry under deck mud on concrete?
Yes. A thinset slurry acts as a bonding coat so the deck mud adheres to the concrete slab. Without it, the mud bed can debond over time.
Q. Should I glue the drain before floating the shower floor?
Dry-fit first, verify position and height, then glue once you’re confident. Many installs benefit from leaving final glue-up until alignment is confirmed, especially if you’re tying into an existing waste line.
Q. What’s the purpose of leaving a “lip” on the perimeter?
That lip acts as a reference edge for checking depth and slope. It helps you measure consistently and keeps your recess boundaries clean.
Q. Is lowering a slab shower something a DIYer can do?
Yes, if you’re comfortable with power tools, concrete dust control, and you take your time with layout and slope. The work is physical and messy, but it’s doable with the right tools and patience.
Final Thoughts
Lowering a concrete floor for a shower pan isn’t glamorous work. It’s loud, dusty, and it makes your bathroom look worse before it gets better. But it’s one of those steps that sets the tone for everything after it.
If you take your time on the layout, cut your perimeter clean, break out the slab with control, and float a proper slope with a real bond coat, you end up with a shower base that feels professional. The drain sits right. The water moves. And you’re not trying to hide mistakes under tile.
If you want to keep sharpening this kind of skill with other setters and contractors who actually do this stuff every day, hop into the Tile Coach Forum. And if you want more walkthroughs like this, get on the newsletter so you don’t miss the next one.
Thanks for reading — I love being your Tile Coach.
Until next time, stay safe, stay precise, and as always — happy tiling!