In this guide
A tiled shower curb helps contain water and creates a finished transition between the shower and bathroom floor. But tile and grout are not waterproof, so a successful installation depends on the waterproofing beneath them as much as on careful tile work. This guide explains how to prepare, waterproof, slope, tile, and finish a shower curb, while highlighting common mistakes that can lead to leaks or loose tile. Because curb construction varies by shower system, the membrane manufacturer’s instructions and applicable local code should guide every step.
Understand the Shower Curb Before Tiling
A shower curb is the raised threshold at the shower entrance. It typically has an inside face, a top, and an outside face. Each surface must be covered by a compatible waterproofing system before tile is installed. Tile, grout, and ordinary caulk alone do not stop water from reaching the framing or subfloor.
The curb’s waterproofing must connect properly to the shower floor and adjoining walls. That connection is especially important at the lower corners, where a gap or poorly sealed transition can let water escape. The correct details depend on whether the shower uses a sheet membrane, a liquid-applied membrane, or a traditional liner system. Do not combine components from different systems unless their manufacturers specifically approve the combination.
Identify the shower system before beginning. Check its installation instructions for approved curb materials, membrane overlaps, corner pieces, mortar, and sealants. If the curb has already been built, confirm that its construction and waterproofing match those instructions. A tile surface can hide a waterproofing problem; it cannot correct one.
Plan the Curb’s Slope and Tile Layout
The top of the curb should slope slightly toward the shower so water drains into the shower rather than toward the bathroom. A commonly used target is approximately 1/8 to 1/4 inch of fall across the curb’s top, subject to the shower-system instructions and local requirements. Check the slope with a level and a small shim or ruler. The top should not be flat or slope outward.
Plan the layout before mixing mortar. Measure the curb’s length, width, and finished height, taking the planned tile and setting-bed thickness into account. Dry-lay the pieces when possible to see where cuts and grout joints will land. A balanced layout usually looks better than a narrow sliver at one end. Consider how curb joints will line up with nearby wall or floor joints, but do not compromise the waterproofing or slope just to force a pattern match.
Decide how the top will be finished. Options include a single-piece stone sill, a manufactured threshold, or multiple tiles. A one-piece sill can reduce the number of joints across the top, but it still needs proper support, waterproofing beneath it, and an inward slope. If using multiple tiles, plan the joints so water can drain and the pieces sit securely without unsupported edges.
Gather Tools and Materials
Use products approved for the specific shower system and tile. Typical supplies include the appropriate curb substrate, waterproofing membrane and accessories, tile, compatible thinset mortar, grout, and a flexible sealant for changes of plane. Some systems require proprietary corners or sealants. Confirm compatibility before purchasing or opening materials.
- Measuring and layout: tape measure, pencil, square, level, straightedge, and tile spacers.
- Tile work: wet saw or suitable tile cutter, mixing bucket, drill with mixing paddle, and notched trowel sized to the tile and manufacturer’s guidance.
- Waterproofing: system-approved membrane, corner pieces, reinforcing fabric, and compatible sealant or mortar as specified.
- Finishing: grout float, sponges, clean water, and appropriate grout or movement-joint sealant.
- Safety: eye protection, hearing protection when cutting, gloves, and a dust mask or respirator appropriate for the task.
Tile cutting can create hazardous dust, particularly when cutting products that contain crystalline silica. Use a wet-cutting method when suitable, follow tool instructions, and control dust. Keep electrical equipment and cords away from standing water.
Prepare the Curb and Waterproof It
Inspect the curb before tiling. It should be solid, clean, properly shaped, and free of loose material, protruding fasteners, and movement. The substrate must be appropriate for the shower system. Do not assume that ordinary wood, drywall, or cement board is ready for tile just because it looks flat; its suitability depends on the complete assembly and the system’s instructions.
Build or correct the inward slope before applying the membrane, where the system’s design requires it. Use a straightedge and level to check the top from end to end and from the shower side to the bathroom side. Fix unevenness or an outward slope before waterproofing. A membrane should follow a sound, properly shaped surface, not be used to disguise a defective curb.
Apply the waterproofing according to the manufacturer’s details. For a sheet membrane, that may involve mortar or adhesive, specific overlaps, and preformed inside and outside corners. For a liquid membrane, it may require a specified number of coats, reinforcing fabric at transitions, and a minimum wet-film thickness. Follow the required drying or curing times. Pay particular attention to where the curb meets the shower floor and walls.
Avoid puncturing the waterproofing on the top or inside face of the curb. Fasteners through those areas can create leak paths. Some traditional liner-based assemblies have specific rules for fastening only above the liner’s required height, while surface-applied systems use different details. Follow the exact instructions for the system in place; do not use one system’s fastening rules for another.
Where required, perform the shower system’s flood test before tile installation. The test checks the waterproofed shower assembly for leaks and should be conducted according to the manufacturer’s instructions and applicable local requirements. Tiling over a known leak makes repairs substantially harder.
Measure, Cut, and Dry-Fit the Tile
Measure each curb face separately. The inside and outside faces may differ in height because of the shower floor, bathroom floor, or curb profile. Account for grout joints and the intended edge finish. If the tile edges will be exposed, use a finished edge, matching trim, or another suitable detail rather than leaving a sharp, unfinished cut where the design requires protection.
Mark cuts carefully and dry-fit every piece before setting it. Check that the top pieces maintain the inward slope, that the side tiles meet the top cleanly, and that planned grout joints remain consistent. For a stone or manufactured sill, verify its overhang and support requirements. Do not leave a broad unsupported projection that could crack under normal use.
Use a wet saw or the appropriate cutter for the tile type. Make cuts slowly to reduce chipping, and smooth sharp edges with a tile rubbing stone if the material permits. Keep the pieces in installation order so they are easy to place once mortar is mixed.
Set the Curb Tile
Mix the specified thinset mortar exactly as directed. Observe the correct water ratio, mixing procedure, slake time, and pot life. Do not add water to mortar that has started to stiffen, and discard material that is past its usable working time. The right mortar depends on the tile and waterproofing system; a product suitable for one assembly may not be approved for another.
Spread mortar only over an area that can be covered while the mortar remains workable. Comb it in consistent ridges using the recommended trowel. Press each tile into place with a slight back-and-forth motion to collapse the ridges and improve coverage. Lift an occasional tile to check contact, especially on the top and on larger pieces. Correct coverage matters because voids can weaken the bond and allow water to collect beneath tile.
Install the curb pieces in the order that best suits the layout and the system’s instructions. Many installers set the inside and outside faces, then place the top pieces, but a one-piece sill or a particular edge detail may call for a different sequence. Maintain the planned grout joints and check alignment frequently with a level and straightedge. Keep the top sloped inward; do not flatten it while adjusting the tile.
Remove mortar from the joints and tile surfaces before it hardens, taking care not to damage or displace the waterproofing. Use spacers if needed, but do not force them into membrane joints or use them in a way that compromises the system. Let the mortar cure for the time stated on its packaging before grouting or placing weight on the curb.
Grout and Seal the Movement Joints
Choose grout suited to the tile and joint width. Cementitious grout and epoxy grout have different installation and cleaning requirements, so follow the product instructions. Pack grout firmly into the tile joints with a float, then remove excess material and clean the surface at the recommended stage. Avoid washing out joints or leaving a heavy grout haze.
Changes of plane—such as where the curb top meets a vertical face—generally require a flexible movement joint rather than rigid grout. Use a sealant approved for the tile and shower system, commonly a suitable 100% silicone product, and follow its preparation and curing instructions. Some systems specify particular sealants or joint details. Do not substitute grout for a required movement joint.
Allow grout and sealant to cure for the time each manufacturer specifies before exposing the curb to water. Cure times vary by product, temperature, humidity, and installation conditions. Keep the shower dry during that period, and do not assume that a surface that feels dry is ready for use.
Common Shower Curb Tiling Mistakes
- Relying on tile or grout for waterproofing: Both are part of the finished surface, not a replacement for a continuous shower membrane.
- Creating an outward or flat top: Water can drain toward the bathroom or remain on the curb instead of flowing into the shower.
- Puncturing the curb membrane: Unapproved screws, nails, or other fasteners can create leak paths, especially on the top or shower-facing side.
- Skipping corner details: Poor transitions at the curb, walls, and shower floor are common weak points in waterproofing.
- Using incompatible products: Mortar, membrane, sealant, and tile must work together as an approved assembly.
- Setting tile over a moving or uneven curb: Movement and inadequate support can cause cracks, loose tile, or failed joints.
- Grouting every change of plane: Rigid grout may crack where surfaces meet; use the movement-joint detail required by the system.
When to Call a Professional
Professional help is sensible when the curb has an existing leak, damaged framing, uncertain liner or membrane details, or a complicated connection to a curbless shower or unusual floor. A tile installer experienced with the specific waterproofing system can inspect the assembly before the work is covered. Local building codes and adopted plumbing requirements can also affect shower construction, so the authority having jurisdiction or a qualified contractor can help clarify local rules.
For a straightforward project, careful planning and strict adherence to the product instructions are essential. The most durable shower curb is not simply the one with neatly cut tile; it is the one built on a solid, correctly sloped, continuously waterproofed foundation.