Why You Shouldn’t Cut Corners on Bathroom Waterproofing

Key Takeaways

• Prevent costly damage: proper waterproofing avoids leaks and water damage in your bathroom.
• Protect your home’s structure: waterproofing stops water penetrating floors and walls.
• DIY is possible: manageable with the right tools and products.
• Long-term durability: use high-quality, tested products.

The Importance of Proper Waterproofing

In a perfect world, water would stay neatly in the bath, shower or sink. In reality, splashes and spills are unavoidable. Without proper waterproofing, even small leaks can cause major problems over time.

Poor waterproofing in a bathroom can lead to:

• Loose or lifting tiles
• Mould or mildew growth in corners
• Damp patches or bubbling plaster on adjoining walls
• Musty odours or visible water damage

Effective waterproofing prevents water from seeping behind tiles and into floors or walls, protecting both your home’s structure and its value. Consider Soudal’s Soudagum LM liquid waterproofing membrane to create a flexible, continuous barrier under tiles that blocks moisture and reduces the risk of mould and costly repairs.

Common Signs of a Leaking Bathroom

Even when tiles look perfectly sealed, water can still sneak through weak points. Look out for these early warning signs:

• Discolouration or cracking grout
• Peeling paint or plaster on walls or ceilings near the bathroom
• Loose or hollow-sounding tiles
• Musty smell or visible mould in corners or on adjoining walls
• Water stains in rooms next to or below the bathroom

If you notice any of these, water may already have penetrated beneath surface layers.

Why Bathroom Leaks Are Hard to Detect

Water damage develops slowly. Moisture may seep behind tiles for months before it becomes visible. By the time you notice swelling plaster or mould, the problem could be extensive, sometimes affecting neighbouring rooms or units.

Unprotected plasterboard, brick or insulation can deteriorate when wet, leading to structural damage and reduced thermal performance. Ensure you reinforce junctions with Soudatape ST reinforcement tape to create a durable, watertight seal.

Typical Causes of Bathroom Water Leaks

Leaks most often occur around:

• Shower trays or tiled shower bases with poor joint sealing
• Gaps between the bathtub and wall
• Poor drainage waterproofing near floor wastes
• Loose plumbing fittings or taps
• Inadequate or missing waterproof membranes beneath tiles

Grout alone is not waterproof. Use a full-coverage membrane such as Soudagum LM, to create a flexible, watertight barrier beneath tiles that prevents moisture from seeping into the substrate and causing long-term damage.

What Bathroom Waterproofing Really Means

You don’t need to waterproof every inch, but you must seal all wet zones where water regularly hits or splashes:

• Showers (bases and walls)
• Bathtubs and surrounding walls
• Around basins and vanities
• Floor areas exposed to direct water contact

Apply a liquid membrane under the tiles and reinforce with tapes and corner seals to stop leaks at junctions. 

Recommended Waterproofing Products and Materials

1. Liquid Waterproofing Membranes

A flexible, spreadable membrane is ideal around showers, bathtubs and washbasins.

2. Reinforcement Tapes and Seals

Corners, edges and pipe penetrations are weak points where leaks often start. Use:

• Soudatape ST – for bends and edges
• Soudatape OC – for outer corners
• Soudatape IC – for inner corners
• Soudatape PD – for pipes and drains

These create a continuous, watertight seal between membrane layers.

3. Finishing Materials

After waterproofing, use flexible tile adhesive and anti-mould grout to secure your tiles, like Soudabond MT Adhesive Paste. Seal all joints and fixtures with an All Purpose Silicone to provide a long-lasting, watertight finish that resists mould growth and keeps your bathroom surfaces clean and protected.

Step-by-Step: How to Waterproof a Bathroom

1. Prepare the Surface

• Clean, stable and dry substrate
• Repair cracks or uneven areas before applying the membrane

2. Apply the Liquid Membrane

• Use brush, roller or trowel
• Apply at least two coats per instructions
• Take the coating up the wall to at least tile height

3. Reinforce Corners and Joints

• Install sealing tape at edges, floor-wall junctions and pipe penetrations

4. Allow to Dry

• Most modern membranes dry within 12–24 hours

5. Tile and Finish

• Use flexible adhesive and anti-mould grout
• Seal sanitary fixtures with coloured silicone 

Check out our video on Waterproofing Systems for more information.

DIY vs Professional Waterproofing

When deciding between DIY and professional waterproofing, it’s important to weigh the pros and cons. The table below compares the key aspects of each option to help you make an informed decision based on your needs and expertise.

Choose Quality Waterproofing Products 

For lasting protection, use professional-grade waterproofing systems. Soudal offers a full range of products for bathroom and wet-area waterproofing, from liquid membranes and sealing tapes to primers and sanitary silicones.

With Soudal products, you can achieve long-term water resistance, prevent damage, and maintain a safe, healthy bathroom environment.