How to Build a Watertight Shower Curb

Water is the ultimate enemy of a bathroom floor. A shower curb serves as the primary barrier preventing overflow from soaking into your subfloor and wall framing. When done well, the curb is not just a threshold; it is a seamless, waterproof transition that keeps your bathroom dry for years to come. Building a curb requires precision and a refusal to cut corners on waterproofing. Whether you are framing with lumber or stacking blocks, the goal is total structural integrity. If there is a weak point in the curb's construction, water will eventually find it, leading to rot and mold that are far more expensive to repair than doing it right the first time.

1. Define the curb footprint. Snap a chalk line on the subfloor to define the exact footprint of the curb. Ensure it aligns perfectly with the shower walls and allows for the thickness of your backer board and tile.
2. Lock down the base plate. Secure your base plate (pressure-treated 2x4) to the subfloor using masonry screws if on concrete or construction adhesive and galvanized nails if on wood. Ensure the connection is rock solid.
3. Stack your curb height. Build the curb to the desired height—typically 4 to 6 inches—by stacking pressure-treated boards on top of the base plate. Screw these into the base plate using long deck screws every 8 inches.
4. Clean and seal gaps. Clean all debris from the curb and surrounding floor area. Apply a thin set mortar or specific sealant to bridge the gap between the curb and the shower floor membrane.
5. Seal every surface watertight. Wrap the entire curb in a waterproof liner or high-grade liquid waterproofing membrane. Ensure the material overlaps the shower pan liner by at least 6 inches on both sides.
6. Board and seal all seams. Attach cement backer board to the sides of the curb using corrosion-resistant screws. Seal all seams and joints with alkali-resistant mesh tape and thin-set mortar.