The shower curb is the raised threshold at the entrance to the shower. It keeps water inside the shower and takes more abuse than any other part of the tile installation except the floor. It gets stepped on, kicked, and splashed. It carries the weight of the glass door or the shower curtain rod. A shower curb that fails leaks water into the subfloor and the room outside the shower. The tiling is cosmetic. The waterproofing underneath is what matters.
Tiling a shower curb takes three to five hours, assumes the waterproofing is already done, and requires careful tile selection because a standard 4-inch-wide curb does not fit full-size wall tiles without cutting. Here is how to choose the right tile, plan the layout, and install it so water drains into the shower, not onto the bathroom floor.
Waterproofing Must Be Done Before Tile Touches the Curb
If you are building a new shower curb, the waterproofing must be complete before tiling begins. There are three common curb waterproofing methods. A solid surface curb made from a single piece of stone, quartz, or solid surface material requires no tiling because the material itself is the finished surface. This is the simplest option and the most waterproof because there are no grout joints. A foam curb from a shower waterproofing system is wrapped in waterproof membrane that laps onto the shower pan and up the walls. This is lightweight and easy to cut to fit. A wood-framed curb built from stacked 2-by-4s covered with cement board and then waterproofed with a liquid membrane or sheet membrane. This is the traditional method and the most common in older homes.
If you are tiling over an existing curb that is leaking or has cracked grout, the tile failure is usually a symptom of failed waterproofing underneath. Tiling over a curb with failed waterproofing guarantees the new tile will fail the same way. Remove the old tile, assess the waterproofing, repair or replace it, and then tile. Do not tile over a curb you do not trust.
Choosing Tile for a Shower Curb
The curb top is typically 4 to 6 inches wide. Standard wall tiles are 12 inches or larger, which means every tile on the curb must be cut. Accept this and plan for it. Do not try to find a tile that fits the curb width perfectly without cutting. That tile does not exist.
Smaller tiles work better on a curb for three reasons. Mosaic tiles, 2-inch or smaller, conform to the slight slope of the curb top without lippage. Slip resistance is higher on smaller tiles with more grout joints, which matters on a surface you step on. Fewer cuts are required, and the cuts that are needed are less visible because the tile pattern hides them.
If you are using the same tile as the bathroom floor or shower walls, bullnose tiles with a finished edge are the best choice for the curb edges. The bullnose creates a clean finished edge on the top outside corner where the curb meets the bathroom floor. If bullnose tiles are not available in your tile series, a metal tile edging profile in a matching finish creates a clean edge and protects the cut tile edge from chipping.
Do not use glossy or polished tile on the curb top. When wet, these surfaces are dangerously slippery for a surface you step onto. Use matte, textured, or mosaic tile with grout joints that provide traction.
The Curb Top Must Slope Into the Shower
The top of the curb is not flat. It slopes inward toward the shower by approximately 1/8 inch per foot. This is a subtle slope that is built into the waterproofing layer before tiling. The tile follows the slope of the substrate underneath. If the waterproofing is flat, add a thin layer of thinset mortar on top of the waterproofing, shaped with a slight inward slope, and let it cure before tiling. Do not try to create the slope by varying the thickness of the thinset under each tile. This is impossible to do consistently. The slope must be built into the substrate.
If water pools on the outside half of the curb instead of draining into the shower, the curb will fail. Water that sits on the grout joints eventually penetrates through to the waterproofing layer. The curb’s only defense is drainage. Tile and grout are the first line. Slope is the real protection.
Plan Your Layout Before You Mix Thinset
Dry-lay the tiles on the curb before applying thinset. The layout order determines how the finished curb looks and where the cuts are visible. There are two approaches.
Top tile overlaps the sides. The tile on the top of the curb extends slightly over the inside and outside vertical faces. This is the preferred layout because water running down the inside face does not hit a horizontal grout joint and sit there. The top tile sheds water onto the vertical tiles below it.
Sides meet the top tile at a corner. The vertical tiles on the inside and outside faces extend up to meet the top tile at a grout joint on the top outside corner. This is easier to cut but creates a grout joint on the top edge of the curb where water can sit. If you use this layout, the joint gets silicone caulk, not grout, to prevent water penetration.
Measure the curb width at both ends and in the middle. The width is rarely perfectly consistent. Cut your tiles to fit the narrowest point, then adjust individual cuts as needed. A tile that overhangs the edge by an eighth of an inch is a sharp edge waiting to chip. A tile that falls short by an eighth of an inch leaves a grout joint wider than the rest of the field, which is visually conspicuous.
Install the Tiles in the Right Order
Install the inside vertical face first. The tiles on the inside of the curb are the least visible and the most forgiving of small cutting errors. Use this face to dial in your technique and your thinset consistency. Spread thinset on the waterproofed curb face with a 1/4-inch notched trowel. Press each tile firmly into the thinset with a slight twisting motion to collapse the ridges and achieve full coverage. Use tile spacers to maintain consistent grout joints.
Install the outside vertical face next. If you are using bullnose tiles, the bullnose goes on the top of the outside face with the finished edge wrapping over the top corner. If you are using a metal edge profile, install the profile first, bedded in thinset, then place the tiles against it.
Install the top tiles last. The top surface is the most visible and receives the most scrutiny. The cuts must be clean. The tiles must be level across the width of the curb so water drains evenly toward the shower. Check the slope with a level after placing each tile. A top tile that tilts outward creates a puddle outside the shower.
Back-butter every top tile. The curb top takes more weight and more water than any other tiled surface in the bathroom. A tile with less than 90 percent thinset coverage will crack under foot pressure. Spread thinset on the substrate and a thin layer on the back of the tile before placing it. Press firmly and check coverage by lifting a tile occasionally during installation. The back of the tile should show full contact with the thinset with no bare spots.
Grout and Seal the Curb
Let the thinset cure for at least 24 hours before grouting. Use unsanded grout for joints narrower than 1/8 inch. Use sanded grout for joints of 1/8 inch or wider. The grout joints on a curb are subject to movement from thermal expansion and the weight of people stepping on the curb. A polymer-modified grout provides additional flexibility and water resistance.
Apply grout to the joints with a rubber float, pressing it firmly into the joints. Wipe excess grout from the tile surface with a damp sponge. Do not wipe grout out of the joints. The grout must fill the joint completely to prevent water from pooling in low spots.
Replace the grout at every change of plane with silicone caulk. The joint where the inside curb face meets the shower floor gets caulk. The joint where the outside curb face meets the bathroom floor gets caulk. The joint where the curb meets the shower wall on each side gets caulk. Grout cracks at changes of plane. Caulk flexes.
Seal the grout after it cures, typically three to seven days. Use a penetrating grout sealer applied with a small brush or a roller bottle. The curb takes more water than any other vertical surface. Sealing is not optional.
Common Mistakes That Ruin a Shower Curb
Using the wrong thinset. A shower curb requires a polymer-modified thinset rated for wet areas. Standard thinset or premixed mastic in a bucket will soften and fail with repeated water exposure. The label on the thinset bag must say suitable for wet areas or intermittent wet conditions. If it does not, do not use it on a shower curb.
Leaving sharp cut edges exposed. The cut edge of a tile is sharp and unglazed. It absorbs water and stains. On a curb, cut edges should face the shower interior where they are less visible, or they should be covered by a bullnose tile or a metal edge profile. A cut edge on the top outside corner of the curb is a visible eyesore and a chipping hazard.
Flat curb top with no slope. Water pools on a flat curb top instead of draining into the shower. Standing water penetrates the grout, saturates the thinset, and eventually reaches the waterproofing layer. The curb must slope inward. If you did not build the slope into the waterproofing, add it with a thin layer of thinset before tiling.
Frequently Asked Questions
Should I just use a solid surface curb instead of tiling it?
If you are building a new shower or rebuilding a failed curb, a solid surface curb is the better choice. It has no grout joints. It does not leak. It does not need sealing. It is a single piece of stone or solid surface material cut to fit. The cost is $100 to $300 for the material. The labor is far less than tiling. The waterproofing is inherently better. The only reason to tile a curb instead of using a solid surface is aesthetic. You want the curb to match the tile in the rest of the bathroom.
Can I tile over a wood curb?
Yes, but the wood must be completely encapsulated in waterproofing. Bare wood expands and contracts with moisture, which cracks the tile and grout. The waterproofing layer on a wood-framed curb must be continuous with the shower pan membrane and must extend up the walls at least 3 inches above the curb height. If the waterproofing is intact and properly sloped, tiling over a wood-framed curb is the same process as tiling over any other waterproofed curb.
The grout on my existing curb keeps cracking. Can I just regrout it?
Regrouting a cracked curb grout joint without fixing the underlying cause guarantees the new grout will crack too. The crack is caused by movement or water damage. Movement cracks are from a curb that flexes when stepped on, typically a wood-framed curb with inadequate support or failed waterproofing. Water damage cracks are from a curb that has absorbed water into the substrate, which swells and cracks the grout. If the grout cracks repeatedly after regrouting, the curb substrate is compromised. Remove the tile, repair or replace the substrate and waterproofing, and retile.
Last modified: June 14, 2026
