By the WetRoomGuide.co.uk — Expert Advice & Product Reviews for UK Wet Rooms Team · Updated June 2026 · Independent, reader-supported

Wet Room Waterproofing: How to Tanking a Wet Room Floor and Walls UK

Waterproofing a wet room is the difference between a shower that lasts years and one that leaks into your joists within months. In the UK, the process is called "tanking," and it's not optional—building regulations require it. Yet many DIY installers either skip it entirely, do it wrong, or choose the wrong product for their substrate. Get it right, and water stays where it belongs.

What is wet room tanking?

Tanking is the application of a waterproof barrier—usually liquid, tape, or board—to the floor and walls before tiles go down. Unlike a traditional shower enclosure with a tray, a wet room has a sloped floor that drains at a low point. The entire floor and walls around the shower area must be tanked so that if water penetrates the grout and tile, it runs down behind the tile into a waterproof membrane, then into the drainage system beneath the floor.

Without tanking, water seeps through grout joints (which aren't waterproof), through the tile adhesive, and into the substrate. On timber joists, this causes rot. On concrete, it can crack and weaken the structure over time. The tanking layer stops water reaching the substrate entirely.

Liquid membrane systems

Liquid membranes are the most common choice for DIY wet room builds. You brush or roll them onto the substrate—usually plasterboard, cement board, or concrete—and they cure to form a flexible, rubber-like layer.

Advantages:

• Easy to apply with basic tools
• Seamless finish (no joints to tape)
• Works on curved or complex surfaces
• Good flexibility to accommodate minor movement
• Generally the cheapest option per square metre

Disadvantages:

• Multiple coats required (typically two to three layers, 24 hours between each)
• Time-consuming—a small wet room can take 2–3 days start to finish
• Requires careful mixing and strict temperature control during cure (usually 15–25°C)
• Easy to miss spots or apply too thin
• Not ideal over very porous substrates without a primer

Most UK wet room tanking products are acrylic-based (water-based) or polyurethane (solvent-based). Acrylic is easier to apply and less toxic, but polyurethane offers better flexibility and handles moisture better—especially useful if there's any damp already present.

Tape and board systems

Tanking tape and boards offer a faster alternative, particularly over large areas.

Tape systems involve applying a PVC or bitumen tape over the substrate, then sealing joints and penetrations. Some products use a combination: liquid membrane applied first, then tape over joints.

Advantages:

• Quick installation—often completed in one day
• No curing time between layers
• Less skill required (more forgiving)
• Excellent for large, flat surfaces

Disadvantages:

• Tape edges can lift if not sealed properly
• Not suitable for textured or uneven surfaces
• Requires skilled technique to avoid air pockets under tape
• More expensive per square metre than liquid
• Joint overlap is critical—poor technique leads to water ingress

Boards (sometimes called tanking panels or waterproof boards) are rigid sheets bonded to the substrate. These are less common in domestic wet rooms but used in commercial settings or very large residential installations.

Choosing the right system

The substrate matters most. Over plasterboard (which many UK builders use), a liquid membrane is usually the best choice—it conforms to the slight imperfections and provides a continuous seal. Over cement board or tile backer board, either liquid or tape works. Over concrete, you must check for rising damp first; if present, a liquid polyurethane membrane is preferable as it has better moisture tolerance.

Your skill level and timeline matter too. Liquid is slower but more forgiving if you're careful. Tape is quicker but unforgiving if corners are cut. If you're uncomfortable with either, hire a specialist—waterproofing failure is expensive to fix.

Application essentials

Preparation is non-negotiable. The substrate must be clean, dry, and sound. Dust, loose plaster, or grease stops the membrane bonding. Holes, cracks, or joints must be sealed first—liquid membrane alone won't bridge a gap. Fill with a polyurethane sealant and let it cure.

Corners and junctions are failure points. Where the wall meets the floor, the membrane must be continuous. Many tanking kits include a flexible corner trowel or fabric for reinforcing inside corners. Use it—this is where leaks start.

Penetrations (pipes, drains, soil stacks) need careful sealing. Apply the membrane around them, but seal the actual gap between pipe and substrate with a flexible sealant. Fabric reinforcement tape should be embedded around the base of the pipe.

Drainage must work alongside tanking. The wet room floor needs a proper gradient toward a floor drain (typically 1:60 minimum). If water sits in puddles, it will eventually find a weak spot in the membrane.

Building regulations and standards

In England and Wales, wet rooms must comply with BS 9414:2015, which covers all aspects of waterproofing. Similar standards apply in Scotland and Northern Ireland. The key requirement: a certified, tested waterproofing system. Many proprietary tanking kits carry British Board of Agrément (BBA) certification or third-party testing. Don't use unbranded products or homemade solutions for this—your insurer might not cover damage.

Common mistakes

• Too thin. One coat of liquid membrane isn't enough. Follow the manufacturer's thickness specification—usually 2–3mm total.
• Skipping priming. Porous substrates need a primer to help the membrane bond properly.
• Wet substrate. Any dampness prevents curing. Leave the room to dry fully before starting.
• Wrong product for the substrate. Check compatibility. Not all membranes stick equally well to all surfaces.

Conclusion

Wet room waterproofing is straightforward if done properly, but there's no shortcut. The choice between liquid, tape, or board systems depends on your substrate, budget, and skill level. Invest in a quality system with a warranty, follow the manufacturer's instructions exactly, and take time getting corners and penetrations right. The cost is modest—typically £200–500 for a small bathroom—compared to the cost of treating timber rot or structural damage later.