This is one of the most common questions we get from homeowners in the Treasure Valley, and it makes sense — most houses around here are built on concrete slabs, so when it’s time to redo a bathroom, the question comes up naturally: the concrete is already there, so can we just tile on it?
Short answer: yes, you can tile a shower floor right on a concrete slab. But “the concrete is already there” is not the same as “the concrete is ready.” A slab shower floor needs two things done right — slope and waterproofing — and if either one is wrong, you won’t know for a few years.
The slope problem
A shower floor is not flat. It has to slope toward the drain — about a quarter inch per foot — so water runs off instead of standing in a corner. Concrete slabs are poured flat. So the slope has to be built, either with a mortar bed (a shaped layer of deck mud troweled to the right pitch) or with a pre-sloped foam pan system that sits on the slab.
This is the part that separates a shower that drains from a shower that puddles. A puddling shower isn’t just annoying — standing water works on grout and sealer every single day, and it’s the first thing that fails. A good installer checks the slope with a level as the bed goes in, not after the tile is set. Once tile is on a flat spot, the only fix is tearing it out.
If your existing slab has already been cut out for plumbing — which is common in a remodel where the drain is moving — you’re starting from scratch anyway, and that’s actually a good thing. A fresh mortar bed on a clean, prepped slab is the most reliable shower floor there is.
Waterproofing: the part that decides everything
Here’s the thing people miss: tile and grout are not waterproof. Water gets through grout joints — that’s normal and expected. What keeps that water from soaking into your slab, wicking into the wall framing, and rotting things you can’t see is the waterproofing layer underneath the tile.
Concrete is porous. It wicks water. A shower built on a bare slab with no waterproofing will move moisture into the slab and out into the surrounding framing, slowly, for years. By the time you notice — a soft spot in the drywall outside the shower, a musty smell — the damage is done and the fix is a full tear-out.
There are a few proven ways to waterproof a slab shower, and they all work when they’re installed right:
Sheet membrane systems (like Schluter-Kerdi). A waterproof membrane bonds over the backer and the mortar bed, and the whole shower — walls, floor, corners, curb — becomes one sealed system. This is the approach we use most. It’s the most forgiving of the options because the membrane is a physical barrier, not a coating that depends on perfect application thickness.
Foam board and pan systems (like Wedi or USG). Pre-sloped foam pans and foam wall boards with sealed joints. Faster to install, consistent slope built in, and the system is designed to work together. The joints and seams are the critical part — they have to be sealed to spec, every one of them.
Liquid membranes (like RedGard). A liquid waterproofing rolled onto cement backer in multiple coats. Works well when applied to the manufacturer’s thickness — and that’s the catch. Too thin in one spot and you have a weak point you can’t see. It takes a careful hand and a wet-film gauge, not just a roller and a guess.
What doesn’t work: relying on caulk to make something waterproof. Caulk is a finish detail, not a waterproofing system. Any shower that depends on a bead of silicone to keep water out of the wall will fail — it’s just a question of when.
Pre-made pan vs. custom mortar bed
If you don’t want a fully tiled shower floor, a pre-made pan is a solid option. Acrylic and cast-iron bases are reliable, they’re fast, and they take the slope question off the table entirely. A pre-made pan with tiled walls above it is a good shower — plenty of houses have them and they’ll last decades.
A custom tiled floor with a mortar bed costs more and takes longer, but it gives you a shower floor that matches the walls, a linear drain if you want one, and a curb height and size that fit your bathroom instead of the other way around.
Linear drains — worth it?
Linear drains are the long, narrow drains you see in high-end showers, usually set along one wall or at the entry. They look great and they let you use large-format tile on the shower floor, because the floor only has to slope in one direction instead of four ways toward a center drain. They cost more — the drain itself, plus the waterproofing detail around it — and they need to be installed exactly right or they leak at the connection. They’re an aspiration, not a necessity. A well-built center-drain shower with a proper slope works just as well and costs less.
Why failures show up years later
This is the part that catches people off guard. A badly waterproofed shower looks perfect on day one. The tile is straight, the grout is clean, the glass is in. The failure takes two, three, five years to show — because water moves slowly through grout and concrete, and the damage happens behind the tile where nobody can see it.
That’s why the cheapest bid on a tile shower should make you nervous. Waterproofing is invisible once the tile goes up, so it’s the easiest place for a low bidder to save a few hundred dollars. You find out years later, and by then the fix is tearing the whole shower out to the studs.
A standard custom tile shower with us runs $1,900–$3,200, and the waterproofing is in that number, not an add-on. We’ll walk you through which system we’re using and why, before we start.
The bottom line
Yes, you can tile a shower right on a concrete slab — most Treasure Valley homes are built that way, and a properly built slab shower lasts decades. The keys are a real slope to the drain and a real waterproofing system underneath the tile, installed by someone who does it often and does it to spec.
Get a straight answer for your bathroom
Call (986) 273-5409 and we’ll come look at your bathroom free — check the slab, talk through pan vs. tiled floor, linear drain vs. center drain, and the waterproofing system that fits your shower. Written price, no pressure, anywhere in Boise, Nampa, Meridian, Eagle, Star, Kuna, Caldwell, Middleton, and Garden City.
Boise Home Flooring — the interior division of Boise Epoxy Flooring Co. (BEFCO), based in Nampa. 18 years in the trades. Tile, LVP, laminate, hardwood, and trim.