Waterproofing is the stage that protects your new bathroom from leaks, moisture damage, mold, and expensive hidden failures.

Important to understand that tile and grout are not the waterproofing system. They are the visible finish. The real protection is the layer underneath: the shower pan, wall membrane, sealed seams, corners, drain connection, curb, niche, bench, and all transition points where water can escape if the system is not installed correctly.

What Exactly Waterproofing Includes

Depending on your bathroom design, waterproofing works may include the shower floor, shower walls, tub surround, curb, bench, niche, corners, seams, drain area, and sometimes the bathroom floor outside the shower.

Common waterproofing systems include hot-mop shower pans, sheet membranes, foam-board systems, PVC or similar pan liners, and liquid-applied roll/brush-on waterproofing membrane (like the RedGard one on the photo on top) — a product that is rolled or brushed on and dries into a waterproof layer.

The exact system depends on the shower type, tile plan, drain type, manufacturer requirements, and local inspection expectations.

California Plumbing Code has several specific requirements for the waterproofing. For example, shower pan lining is commonly required to slope toward weep holes, extend at least 3 inches above the finished dam/threshold, and avoid nails/perforations too low near the curb area. For the visible shower/tub wall area, California residential bathroom requirements commonly refer to a smooth, hard, nonabsorbent surface in shower/tub areas, extending 72 inches above the floor. And a few other requirements that must be executed properly, otherwise waterproofing city inspection will be failed. 

Waterproofing Test: Shower Pan & Flood Test

Before tile is installed, the shower pan and wet area may need to be tested. This is commonly called a flood test or shower pan test.

The drain is temporarily plugged, the shower pan is filled with water, and the water level is monitored to confirm there are no leaks before the area is covered with tile. Some cities require the pan to be filled to the rough threshold, and some may require a 24-hour test depending on local rules and inspection practice.

This is one of the reasons waterproofing cannot be rushed. Once tile is installed, the waterproofing is hidden.

Standard Showers vs. Curbless Showers

All bathrooms need proper waterproofing, but with standard showers the system is usually more straightforward than with curbless ones. Curbless showers, wet rooms, linear drains, benches, niches, and larger custom showers require more planning. The slope, drain location, waterproofing extension, and bathroom floor transitions all need to work together. Some designs that look beautiful on the picture can become risky if the bathroom floor height, drain position, or waterproofing path is not realistic for the existing home.

This is where practical design matters. A good bathroom design must be buildable, drain properly, and protect the home — not just look good in a rendering.

Why This Step Cannot Be Skipped

Bad waterproofing may not fail immediately. A bathroom can look perfect on day one and still have problems hidden behind the tile.

Months or years later, poor waterproofing can lead to leaks, swollen framing, mold, damaged subfloor, loose tile, stains on ceilings below, and in the worst cases, with waterproofing fails simple repair won’t cut it – the entire bathroom has to be taken apart and rebuilt.

At that point, the repair is no longer small. It may require demolition, new waterproofing, new tile, new inspections, and rebuilding finished areas that were already paid for before.

So the goal is simple: before the beautiful finishes go in, the bathroom must be properly protected underneath.