Tile is one of the best finishes you can put in a wet area, but a lot of homeowners (and more than a few rookie installers) assume that means a tiled shower is waterproof. It isn't. Tile, grout and even cement backer board are water-resistant. The only thing that makes a tile assembly waterproof is a proper waterproofing layer underneath it. Knowing the difference is what separates a shower that lasts 30 years from one that rots out the subfloor in five.
Waterproof vs. Water-Resistant: The Short Answer
- Water-sensitive materials break down when they get wet. Standard drywall, plywood, OSB and most wood framing fall into this group.
- Water-resistant materials can get wet without falling apart, but water can still pass through them. Ceramic and porcelain tile, cement-based grout, thinset mortar and cement backer board are all water-resistant.
- Waterproof materials stop water completely. A sheet membrane, a liquid-applied membrane or a foam board system rated as waterproof keeps water from ever reaching the framing or subfloor.
Why Tile and Grout Aren't Enough
Even dense porcelain tile is only as watertight as the joints around it, and cement-based grout is porous. Every shower soaks the grout lines, and water wicks through them into the thinset and backer board behind. Cement board doesn't fall apart when it gets wet, which is why it's called water-resistant, but it passes moisture straight through to the studs and drywall behind it.
The trouble is that this kind of failure is slow and hidden. By the time you see loose tile, cracked grout, a musty smell or a stain on the ceiling below, the framing has usually been wet for a long time. Tearing out and rebuilding a shower costs far more than doing the waterproofing right the first time.
Where You Need True Waterproofing
- Shower walls and shower floors, including curbs, benches and niches
- Tub surrounds, especially with a hand shower or rain head
- Steam showers, which also need a vapor-tight system
- Wet rooms and curbless showers
- Laundry rooms, mudrooms and any floor over finished space where a leak would do damage
Kitchen backsplashes and most dry floors only need a water-resistant installation. If you're not sure, waterproof it. The added cost is small compared to the cost of a repair.
Your Waterproofing Options
Liquid-applied membranes
Roll-on or trowel-on membranes like Laticrete Hydro Ban go on over cement board or other approved substrates and cure into a seamless, rubbery waterproof layer. Reinforce changes of plane and seams with sealing tape, pre-formed outside corners and pipe collars, then apply to the thickness the manufacturer specifies. Most installers use a wet-film gauge to check.
Sheet membranes
Sheet membranes such as Schluter Kerdi are set in thinset over the substrate, with overlapping seams and pre-formed corners. Thickness is controlled at the factory, so coverage is consistent. Use the trowel the membrane manufacturer recommends, like a Kerdi trowel, to get full coverage under the sheet.
Foam board systems
Waterproof foam backer boards are lightweight, easy to cut and go up fast. They become a waterproof system once the seams and screw heads are sealed with the matching sealant and tape. Hydro Ban boards, for example, use Hydro Ban board screws and washers, with seams sealed using Hydro Ban adhesive and sealant.
Floors
On floors, an uncoupling membrane like Schluter Ditra protects tile from cracking when the substrate moves, and it can serve as a waterproof layer when the seams are properly sealed. For shower floors, use a waterproof shower pan system with a bonded drain, and make sure the floor slopes to the drain.
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Tips for a Waterproof Shower That Passes Inspection
- Use a rated product. Look for membranes that meet ANSI A118.10, the standard for waterproof membranes used under thin-set tile.
- Stay in one system. Don't mix one company's membrane with another company's drain or sealant. Staying in one system keeps the manufacturer's warranty intact.
- Detail the weak spots first. Corners, seams, valves, shower heads, niches and the drain connection are where most leaks start.
- Flood test the floor. Plug the drain and fill the pan with water for at least 24 hours (check your local code and the manufacturer's instructions) before you set tile. It's much easier to fix a leak now than after the tile is down.
- Don't puncture the membrane. Plan grab bars, shelves and glass door hardware ahead of time, and seal any fasteners that go through the waterproof layer.
- Grout and caulk correctly. Grout the joints, then use a flexible sealant at changes of plane and where tile meets the tub or shower pan.
Frequently Asked Questions
Is cement board waterproof? No. Cement board is water-resistant. It won't break down when it gets wet, but water passes through it. In a shower it needs a waterproof membrane on top of it or a vapor barrier behind it, depending on the system.
Is grout waterproof? Cement-based grout is not waterproof, even when sealed. Epoxy grout is much more water- and stain-resistant, but it's still not a replacement for a waterproofing membrane.
Is porcelain tile waterproof? Porcelain tile itself absorbs very little water, but the grout joints around it do. The tiled surface as a whole is water-resistant, not waterproof.
Do I need to waterproof a tub surround? If it gets wet regularly, yes. A waterproof membrane is cheap insurance against hidden water damage behind the tile.
Get Your Waterproofing Supplies at Contractors Direct
Whether you're building a curbless shower, a steam room or a simple tub surround, Contractors Direct carries the waterproofing membranes, shower installation products, thinset and grout and tile tools pros use every day. Questions about which system fits your job? Reach out to us at 1-800-709-0002.