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At The Bathroom Showroom, we believe a dream bathroom should be as durable as it is beautiful. While it’s easy to focus on stylish brassware and sleek tiling, the most critical element of your renovation is often the one you never see: waterproofing.
Water damage is a silent, creeping threat. Because it often starts behind walls or under floorboards, it can remain unspotted for months, leading to structural rot and hazardous mould growth. What begins as a microscopic seep can quickly escalate into a catastrophic failure, resulting in thousands of pounds in repair costs and long-term damage to your home’s integrity.

What This Guide Covers

Before you begin any renovation work, it’s important to understand which areas to prioritise for protection. This guide covers essential tanking and sealing practices to help protect your investment:
  • The Hidden Risks: Identifying why minor damp spots lead to major structural failures.
  • Targeted Prevention: Pinpointing the high-risk zones in your bathroom that require maximum protection.
  • Value Preservation: How proactive waterproofing secures your home’s market value and your peace of mind.

Understanding the True Purpose of Waterproofing

Waterproofing, often referred to in the trade as "tanking", is your bathroom’s invisible suit of armour. Its purpose goes far beyond just stopping a drip; it’s about total moisture management.
  • Mould Prevention: Damp environments are breeding grounds for black mould (Aspergillus niger), which can pose respiratory risks and ruin expensive finishes.
  • Structural Integrity: Over time, water weakens timber joists and erodes mortar. Proper tanking ensures the skeleton of your home stays bone-dry.
  • Investment Protection: A bathroom is one of the most expensive rooms to renovate. Waterproofing ensures you don't have to strip it all back in three years because of a failed subfloor.

The Critical Zones: Where to Waterproof

You don't necessarily need to tank every inch of a bathroom, but "splash zones" require a rigorous approach.
  • Shower Enclosures & Wet Rooms: These are "high-load" areas. In a wet room, the entire floor and all walls (up to at least 2 metres) must be sealed.
  • Bath Surrounds: Even if you don't have a shower over the bath, the joints where the tub meets the wall are primary failure points.
  • Vulnerable Junctions: The floor-to-wall joint (the "perimeter") is where building movement often cracks standard grout, allowing water to seep through.

Your Waterproofing Arsenal: Methods & Materials

Professional installers don't rely on just "waterproof grout" (which is actually porous). They use a layered system:
  • Liquid Tanking Membranes: A thick, paint-on coating, like the OB1 Waterproof Tanking Solution, that dries into a flexible, rubber-like sheet
  • Waterproof Tile Backer Boards: Replaces standard plasterboard. These boards won't rot or lose strength when wet.
  • Cementitious Slurries: Often used for heavy-duty floors, these provide a rigid but breathable waterproof layer.
  • Sealing Tapes & Corners: Self-adhesive or "embedded" tapes used to reinforce the corners where walls meet floors—the most common place for leaks to start.

The Waterproofing Process: A Step-by-Step Guide

  1. Surface Preparation: Surfaces must be clean, dust-free, and primed. Any "bounce" in the floorboards must be eliminated.
  2. Applying Boards/Membranes: Install backer boards or apply the first coat of liquid membrane.
  3. Detailing: This is the most critical step. Apply sealing tapes to all internal corners, joints between boards, and around pipe penetrations.
  4. Curing: You must wait for the membrane to fully dry (usually 12–24 hours) before tiling. Rushing this leads to system failure.

How To Tank a Shower

If you’re considering tackling the tanking yourself, we highly recommend this practical walkthrough from Sharn's House. In this video, Sharn breaks down a standard UK waterproofing kit and demonstrates the exact techniques for a "bulletproof" seal.

DIY vs. Professional Help

DIY Approach
  • Skill Level: Moderate; requires close attention to detail and precision.
  • Tools: Basic equipment like rollers, brushes, and utility knives.
  • Risk: High; errors remain hidden behind tiles until they become expensive structural issues.
Professional Hire
  • Skill Level: Expert; understands complex requirements like floor "falls" and drainage gradients.
  • Tools: Specialised gear such as moisture meters, laser levels, and heavy-duty mixers.
  • Risk: Low. Work is typically guaranteed, providing confidence that potential issues are covered, and help is available if problems occur.

Common Waterproofing Mistakes

Avoid these pitfalls to ensure your bathroom stands the test of time:
  • Inadequate Prep: Applying membranes over dusty or greasy surfaces prevents proper bonding.
  • Incorrect Product Use: Using standard "moisture-resistant" plasterboard in a high-pressure shower area instead of a true waterproof backer board.
  • Rushing Drying Times: Tiling over "tacky" membrane can trap moisture and prevent a full seal.
  • Insufficient Coverage: "Spot-treating" only the corners rather than creating a continuous, unbroken barrier.
(If you have strong tiling and joint-sealing skills, DIY in splash zones is feasible. For wet rooms or upstairs baths, hire a professional to ensure airtight waterproofing.)

When to Call a Pro: The Decision Checklist

While a steady-handed DIYer can handle basic splash-zone sealing, you should strongly consider hiring a professional if any of the following apply:
  • You’re Creating a True Wet Room: Wet rooms require a precise "fall" (slope) in the floor to ensure water hits the drain rather than pooling in corners.
  • The Bathroom is Upstairs: The risk of a leak affecting the ceilings and electrics in the rooms below is significantly higher.
  • You’re Dealing with Uneven Subfloors: If your floorboards are bouncy or uneven, a pro will know how to stabilise them to prevent the waterproofing membrane from cracking.
  • You Need a Guarantee: If you plan to sell your home in the future, having a certificate or guarantee from a professional installer can be a major selling point for savvy buyers.
  • Complex Pipe Layouts: If your plumbing requires multiple penetrations through the floor or walls, a professional ensures these "weak spots" are hermetically sealed.

Ready to Protect Your Bathroom?

A beautiful bathroom is an investment, so avoid compromise from overlooked waterproofing. Make sure you have the correct materials, for both DIYers and professionals, to guarantee a leak-free space.
At The Bathroom Showroom, we stock the complete "Waterproofing Arsenal" mentioned in this guide. From high-performance liquid tanking kits to industry-leading tile backer boards, we provide the same professional-grade products used by the UK’s top installers.
​​Book an appointment with your local Bathroom Showroom. Experts in all things bathrooms, we can help turn your dream bathroom into a reality.