Understanding Different Types of Structural Waterproofing Materials 

When it comes to structural waterproofing, the challenge isn’t just choosing a product, it’s choosing the right system for the job. With tanking membranes, cementicious coatings and liquid-applied systems all available, knowing when to use each one can make the difference between a long-term solution and a costly return visit. 

A clear understanding of how these systems work and where they’re best suited makes it much easier to guide contractors towards the right decision. 

What Is Structural Waterproofing? 

Structural waterproofing refers to protecting a building from water ingress, typically below ground or in areas exposed to constant moisture. It’s commonly required for: 

• Basements and cellars 

• Foundations and slabs 

• Retaining walls 

• Underground structures 

In the UK, systems are often aligned with BS 8102, which defines protection types and performance requirements. 

1. Sheet Membranes (Pre-Formed Systems)

What they are: Factory-produced waterproof sheets, usually supplied in rolls, that are applied to a structure to form a physical barrier against water. 

Common types: 

• Self-adhesive membranes 

• Internal cavity drain membranes 

• Pre-applied membranes 

When to use them: 

• New-build basements 

• External foundation walls 

• Projects where consistent thickness and quality are essential 

Typical applications: 

• Type A (barrier) protection systems 

• Type C protection systems 

• Below-ground external waterproofing 

• Tanking systems 

Advantages: 

• Consistent thickness and performance 

• Reliable when installed correctly 

• Suitable for high water table conditions 

Things to watch: 

• Requires good surface preparation 

• Detailing around penetrations and joints is critical 

• Additional protection/drainage products are usually required 

2. Cementitious Coatings, water plugs and mortars

What they are: Brush, roller, trowel, or spray-applied coatings that bond directly to the substrate to create a waterproof layer. 

Common types: 

• Cementitious tanking slurries 

• Water plugs 

• Waterproof mortars 

When to use them: 

• Internal waterproofing of basements 

• Refurbishment projects 

• Plugging leaks and detailing 

Typical applications: 

• Internal tanking  

• Lift pits and service areas 

• Damp-proofing walls and floors 

Advantages: 

• Easy to apply with basic tools 

• Good for irregular surfaces 

• Cost-effective solution 

Things to watch: 

• Surface preparation is crucial 

• Limited flexibility (some products can crack with movement) 

• May require multiple coats 

3. Liquid-Applied Waterproofing Systems

What they are: Fluid products that cure to form a seamless, flexible waterproof membrane. 

Common types: 

• Polyurethane liquids 

• Resin-based systems 

• Bitumen based coatings 

When to use them: 

• Complex detailing or irregular shapes 

• Roofs, balconies, and podium decks 

• Areas requiring seamless coverage 

Typical applications: 

• Roof waterproofing 

• Podium decks and terraces 

• External tanking 

Advantages: 

• Seamless finish, no joints or overlaps 

• Highly flexible and crack-bridging 

• Ideal for complex detailing 

Things to watch: 

• Application conditions (temperature, moisture) matter 

• Requires correct curing time 

• Some systems need trained installers 

Choosing the Right Structural Waterproofing System: Key Questions to Ask 

• Is this new build or refurbishment? 

• Internal or external application? 

• What’s the substrate (concrete, block, etc.)? 

• Is there hydrostatic pressure (standing water)? 

• How critical is the space (e.g. habitable basement)? 

These answers will guide whether a membrane, coating, or liquid system is most suitable or whether a combined approach is needed. 

Combining Systems for Better Protection 

In many cases, especially below ground, a combined system is the best solution. For example: 

• External membrane (Type A) + internal cavity drain system (Type C) 

• Protection + drainage layer 

This approach adds redundancy and reduces risk, something worth highlighting to contractors working on high-value or habitable spaces. 

Helping customers make informed decisions 

No single waterproofing system fits every job. The key is understanding the application, environment, and installation constraints, then matching the right material to the task. 

At BSSP, the focus is on helping customers make informed decisions, whether that’s selecting the right product, understanding compatibility, or ensuring the system will perform long-term. 

If you’re unsure, it’s always worth taking a moment to ask a few extra questions. It can prevent costly failures and help keep projects moving without delays.