Water is essential in everyday life, but it can become one of the biggest threats to a building when it reaches areas that were designed to remain dry. Roofs, bathrooms, balconies, basements, retaining walls and even concrete structures can all be affected by unwanted moisture if the right protection is not installed.

So, what is waterproofing?

Waterproofing is the process of protecting a surface, structure or building element against unwanted water penetration. It normally involves installing a waterproofing membrane, coating, sheet system or other protective barrier designed to prevent water from passing through the protected area.

In construction, waterproofing is much more than simply applying a waterproof coating. An effective waterproofing system considers the substrate, joints, penetrations, drainage, movement, expected water exposure and the way the area will be used.

Waterproofing may be needed during new construction, renovation or as part of remedial work when an existing building develops leaks, dampness or water ingress.

What Does Waterproofing Mean in Construction?

The simplest waterproofing meaning is creating a barrier that prevents unwanted water from entering or escaping through a building element.

Consider a bathroom, for example. Tiles provide the visible finished surface, but the waterproofing system underneath is what protects the building structure against moisture reaching areas where it can cause damage.

The same principle applies elsewhere.

On a roof, waterproofing helps stop rainwater from penetrating the roof structure. On a balcony or podium, it protects the areas below. Around a basement or retaining wall, the waterproofing system helps prevent groundwater and moisture from entering the structure.

Because every situation is different, there is no single waterproofing product or method that is suitable for every building.

Why Is Waterproofing Important?

Water often finds its way through very small weaknesses within a building. Cracks, joints, penetrations, failed seals and poorly detailed transitions can allow moisture to move into areas that may not be immediately visible.

That means a waterproofing problem can develop for some time before obvious signs begin to appear.

Effective building waterproofing helps protect against:

• Water ingress and leaks
• Dampness within walls and floors
• Mould-supporting moisture conditions
• Deterioration of finishes
• Damage to tiles and coatings
• Timber decay
• Corrosion of reinforcement in concrete
• Damage to rooms or assets below the affected area
• Expensive remedial work later

The purpose is therefore not simply to keep a surface looking dry. Waterproofing helps protect the building envelope, underlying substrate and structural components from continued exposure to moisture.

Waterproof vs Water-Resistant: What Is the Difference?

Although the terms are sometimes used interchangeably, waterproof and water-resistant do not mean exactly the same thing.

A waterproof system is designed to prevent water from passing through the protected building element under the conditions for which the system was designed.

A water-resistant material or surface can resist water exposure to a certain degree but should not automatically be assumed to provide the same protection as a complete waterproofing system.

This distinction is particularly important in wet-area construction. Australian building requirements distinguish between building elements that must be waterproof and those that only need to be water resistant.

For property owners, builders and contractors, the important point is that the waterproofing requirements for an area should be determined by its use, exposure and applicable construction requirements rather than by simply applying a product labelled “water resistant.”

How Does Waterproofing Work?

A properly designed waterproofing system creates a continuous protective layer between water and the building element that needs protection.

The exact installation varies according to the area and waterproofing materials being used, but a typical process can involve several stages.

1. Inspection and Assessment

Before choosing a waterproofing method, the condition of the area needs to be understood.

For new construction, this means considering the substrate, drainage, detailing, expected movement and water exposure.

For an existing leaking building, the first priority is identifying where the water is actually entering and how it is travelling through the structure.

This is particularly important because visible water damage does not always appear directly below the original leak.

Waterseal can use specialist leak detection services, including High Voltage Electronic Leak Detection for appropriate membrane systems, to help identify breaches that may otherwise be difficult to locate.

2. Surface Preparation

Waterproofing performance depends heavily on the condition of the substrate.

Depending on the project, preparation may involve cleaning the surface, addressing defects, treating cracks, correcting unsuitable areas and preparing joints or penetrations.

Applying a high-quality membrane over an unsuitable substrate does not automatically create a reliable waterproofing system.

3. Detailing Critical Areas

Corners, joints, drains, penetrations, changes in material and other transitions can be vulnerable areas.

These details need to be incorporated into the waterproofing design rather than treated as an afterthought.

4. Membrane or Waterproofing System Installation

The selected membrane, coating or sheet system is then installed according to the project requirements and the manufacturer’s system specifications.

5. Protection and Finishing

Depending on the application, the waterproofing membrane may sit underneath tiles, screeds, soil, landscaping, protective boards or other finished surfaces.

The waterproofing therefore often becomes invisible after construction is completed, which makes correct installation at the beginning especially important.

What Are the Main Types of Waterproofing?

There are numerous waterproofing methods and materials available. The correct solution depends on the substrate, location, water exposure, movement, intended finish and project conditions.

Some of the main categories include the following.

Liquid-Applied Waterproofing Membranes

Liquid membranes are applied to a prepared surface and cure to create a continuous protective layer.

Depending on the system, materials may include polyurethane or acrylic-based membranes and other specialist coatings.

Liquid systems can be useful where a waterproofing membrane needs to follow complex shapes, corners and details.

Waterseal uses liquid-applied waterproofing systems in various applications, including specialist wet area waterproofing.

Sheet Membranes

Sheet waterproofing uses manufactured membrane sheets installed over the substrate.

Systems may include PVC, TPO, Butynol and other specialist membranes depending on the application.

Sheet membranes can provide controlled membrane thickness and are commonly used in various roof, commercial and specialist waterproofing applications.

Bituminous and Torch-Applied Systems

Modified bitumen membranes are commonly associated with robust waterproofing applications where a durable membrane system is required.

Waterseal’s roof waterproofing services include experience with multiple membrane technologies, including PVC, polyurethane, acrylic, TPO, Butynol and torch-applied modified bitumen systems.

Waterproof Coatings

Specialist waterproof coatings can be used in applications such as trafficable surfaces, plant areas and other exposed structures.

The coating must be selected according to the conditions it will experience. A system suitable for a protected internal area may not be appropriate for a car park exposed to traffic and weather.

Waterstops and Specialist Civil Systems

Larger civil and below-ground structures often require more than a surface coating alone.

Waterstop systems and specialist membranes may be incorporated into construction to manage water at joints and other vulnerable locations.

Waterseal provides civil waterproofing works for structures including bridges, tunnels, underpasses, retaining walls, tanks and pits.

Where Is Waterproofing Used?

Waterproofing is needed across far more areas of a building than bathrooms alone.

Bathrooms, Showers and Other Wet Areas

Bathrooms, showers, laundries, ensuites and similar spaces regularly experience water and moisture.

Correct wet area waterproofing helps prevent moisture from passing into adjoining building elements.

Australian construction requirements contain specific provisions for waterproofing and water resistance in wet areas, with AS 3740:2021 forming one recognised pathway within the NCC framework for houses.

Balconies, Terraces and Podiums

Exterior areas can experience rainfall, temperature changes, movement and continual environmental exposure.

When balconies or podiums sit above occupied rooms or other sensitive areas, waterproofing failure can affect much more than the surface itself.

A properly selected balcony, terrace and podium waterproofing system should take the substrate, intended use and finished surface into account.

Roofs

Concrete roofs are strong, but cracking and movement can still create pathways for water.

Both new and existing buildings may therefore require roof waterproofing to help protect the slab and occupied spaces beneath it.

Basements and Undercrofts

Below-ground structures face a different type of challenge because moisture can originate from the surrounding ground.

Proper basement and undercroft waterproofing is important for protecting the integrity and usability of below-grade areas.

Retaining Walls

Retaining walls can remain in direct contact with damp soil.

Without appropriate retaining wall waterproofing, moisture may migrate through the wall and cause staining, deterioration or problems on the visible side of the structure.

Roof Gardens and Planter Boxes

Planters and roof gardens combine soil, irrigation and drainage in areas that may sit directly above occupied building spaces.

The waterproofing and drainage system therefore needs to accommodate constant exposure to moisture.

Waterseal provides specialist roof garden and planter box waterproofing for these applications.

Pools, Ponds and Water Features

In some structures, waterproofing is intended to keep water inside rather than prevent it from entering.

Pools, ponds and water features need a correctly selected membrane system to reduce unwanted water loss and protect surrounding building elements.

Car Parks

Car park decks may be exposed to rainfall, traffic, chemicals, movement and significant wear.

Specialised car park waterproofing coatings can help protect the underlying structure while also providing a suitable trafficable finish.

What Happens When Waterproofing Fails?

Waterproofing failure does not always start with water dripping from a ceiling.

Early symptoms can be much less obvious.

Common signs that may indicate a waterproofing or moisture problem include:

• Damp patches on walls or ceilings
• Water stains
• Peeling or bubbling paint
• Persistent musty odours
• Mould growth
• Efflorescence or white mineral deposits
• Cracked or deteriorating finishes
• Loose or drummy tiles
• Water appearing after heavy rainfall
• Moisture around balconies or external walls
• Dampness in basements or below-ground rooms

These symptoms should not automatically be treated as proof that the membrane itself has failed.

Water can enter through roofs, plumbing, windows, joints, façade defects, drainage problems and numerous other locations.

Finding the source of water ingress is therefore usually more valuable than repeatedly treating the visible symptom.

What Is Remedial Waterproofing?

Remedial waterproofing deals with existing structures where water ingress, membrane failure or moisture-related damage has already developed.

Rather than treating every leak in the same way, remedial work should start by identifying the source and understanding the condition of the existing building.

The solution might involve repairing part of a waterproofing system, replacing a failed membrane, sealing particular defects or undertaking more extensive reconstruction.

Waterseal’s remedial waterproofing services focus on locating the source of water ingress and determining appropriate repair options.

This diagnostic approach is important because applying another coating over the visible problem does not necessarily address the pathway through which the water is entering.

Waterproofing and Structural Damp

Not every moisture problem is caused by a failed bathroom or roof membrane.

Buildings may also experience structural damp.

Waterseal identifies three common forms:

Rising damp involves moisture moving upward from the ground through porous building materials.

Falling damp relates to moisture entering from above, potentially through roofs, gutters or other external building components.

Penetrating damp occurs when moisture moves horizontally through external walls or other parts of the building envelope.

If dampness is already present, identifying which process is occurring is important before selecting a treatment.

Learn more about the causes and solutions for structural damp.

Waterproofing in New Construction vs Existing Buildings

Waterproofing is generally easiest to integrate during construction because the building elements are accessible and the waterproofing system can form part of the original design.

The membrane can be coordinated with drainage, joints, penetrations, finishes and other trades before those components become concealed.

Existing buildings can be more complicated.

The first challenge is usually determining why the area is leaking. Finishes may need to be removed, hidden moisture paths investigated or existing membrane conditions assessed.

This is why remedial waterproofing often requires a combination of technical diagnosis and waterproofing expertise rather than simply applying a new product.

How Is the Right Waterproofing System Selected?

There is no universal “best waterproofing membrane.”

The best solution is the system that suits the specific project.

A waterproofing contractor may need to consider:

Location: Is the area internal, external, above ground or below ground?

Water exposure: Will the area experience occasional splashing, rainfall, retained water or continual ground moisture?

Substrate: Is the surface concrete, masonry, sheeting or another material?

Movement: Will the building element experience thermal expansion, vibration or structural movement?

Finished surface: Will the membrane sit beneath tiles, landscaping, trafficable coatings or another finish?

Drainage: How will water leave the area?

Penetrations and joints: Where are the likely vulnerable details?

Existing condition: Is this new construction or a remedial waterproofing project?

System selection should therefore come before product selection.

How Much Does Waterproofing Cost?

Waterproofing costs vary significantly because the work required for a small internal wet area is very different from waterproofing a large commercial roof, basement, podium or civil structure.

Factors affecting the cost can include:

• Size of the area
• Type and condition of the substrate
• Waterproofing system required
• Accessibility
• Surface preparation
• Number of joints and penetrations
• Existing water damage
• Removal of existing finishes
• Drainage or building defects
• Whether the project is new or remedial

For an existing leak, paying for the correct diagnosis can also prevent money being wasted on repairs that address the symptom rather than the actual source.

How Long Does Waterproofing Last?

There is no single lifespan that applies to every waterproofing system.

Performance depends on the membrane type, substrate preparation, workmanship, exposure, building movement, drainage, protection of the membrane and ongoing maintenance.

A correctly selected system installed under suitable conditions can provide long-term protection, while even a high-quality product may perform poorly if the substrate or detailing is unsuitable.

For this reason, waterproofing should be treated as a complete construction system, not simply as a product applied to a surface.

Can Existing Waterproofing Be Tested for Leaks?

Yes. Depending on the membrane type and site conditions, specialist testing methods can help identify membrane defects.

One method used by Waterseal is High Voltage Electronic Leak Detection (HVELD).

HVELD can locate breaches in certain non-conductive waterproof membranes and coatings by using electrical current to identify the position of a defect. This can provide a more targeted approach than removing large areas of finished construction simply to search for a leak.

Waterseal also uses other diagnostic technologies to investigate moisture pathways where required.

Do You Need a Professional Waterproofing Contractor?

Waterproofing performance depends on much more than whether a membrane was applied.

Preparation, system compatibility, membrane thickness, detailing, junctions, penetrations, drainage and curing can all influence the outcome.

Complex commercial, civil, below-ground and remedial projects can require particularly careful system design and installation.

When selecting a waterproofing contractor, consider their:

• Experience with the specific type of project
• Knowledge of different waterproofing systems
• Understanding of relevant Australian requirements
• Ability to diagnose existing leaks
• Experience with both new and remedial work
• Quality of previous projects
• Approach to surface preparation and detailing

Waterseal has been providing waterproofing solutions across Western Australia for decades, covering domestic, commercial and civil projects. You can view examples of completed Waterseal waterproofing projects throughout Perth and WA.

Frequently Asked Questions About Waterproofing

What is waterproofing in simple words?

Waterproofing is the process of creating a barrier that stops unwanted water from passing into or through a building element. It can be used to keep water out of structures such as roofs and basements or to keep water contained within areas such as pools and tanks.

What is a waterproofing membrane?

A waterproofing membrane is a protective layer designed to restrict water penetration. Depending on the application, membranes can be liquid-applied, sheet-based, bituminous or part of another specialist waterproofing system.

Is waterproofing the same as sealing?

Not necessarily. Sealants are often used around individual joints, gaps or penetrations. Waterproofing normally refers to a broader system designed to protect an entire building element or area from water penetration.

Is waterproofing the same as damp proofing?

No. Although both manage moisture, waterproofing and damp-proofing address different conditions. Damp-proofing commonly deals with moisture migration, while waterproofing systems may need to resist more significant water exposure or ingress.

Can you waterproof over existing tiles?

Sometimes remedial systems can be applied to existing construction, but waterproofing over tiles should not automatically be treated as the solution to every leak. The cause and pathway of the water ingress should be identified first.

What areas of a house need waterproofing?

Common residential areas include showers, bathrooms and laundries, as well as external areas such as balconies, terraces, roofs, retaining walls, planter boxes and below-ground structures where appropriate.

What causes waterproofing to fail?

Possible causes include poor surface preparation, unsuitable membrane selection, inadequate detailing, movement, membrane damage, drainage issues, poorly treated penetrations and deterioration over time.

Can waterproofing stop rising damp?

A standard surface waterproofing membrane is not automatically a solution for rising damp. Rising damp has specific causes related to moisture travelling through porous building materials, so the source must be correctly diagnosed before treatment.