Bathroom Waterproofing

The layer you never see, and the one that matters most

Behind every tiled shower and bathroom floor sits a waterproof membrane. Once the tiles are laid you never see it again, yet it decides whether your bathroom lasts thirty years or starts to fail in three. Tiles and grout are not waterproof. Water passes through grout lines and hairline cracks every time you shower. The membrane underneath is what stops that water from reaching the timber, plasterboard and concrete of your home.

Failed waterproofing is one of the most common and costly building defects in Australian homes. Rotting joists, swollen skirting boards, mould on the other side of the wall, lifting floor coverings and stained ceilings below are all signs that water has got where it should not be. Fixing the damage almost always means removing the tiles and starting again.

We take waterproofing seriously. Every wet area we build is waterproofed to the Australian Standard AS 3740, using membrane systems suited to the substrate, installed carefully, allowed to cure fully and documented with photographs for your records. The work is carried out by licensed and insured trades.

What AS 3740 requires

AS 3740, Waterproofing of domestic wet areas, sets out how bathrooms, laundries, toilets and other wet areas in homes must be protected. It divides a bathroom into zones depending on how wet they get, and specifies which surfaces must be waterproof and which must be water resistant. In broad terms:

• The shower floor and walls must be waterproofed, with the wall membrane extending to a set height above the floor.
• The rest of the bathroom floor must be treated, with the extent depending on the floor material and whether there is a floor waste.
• Wall-to-floor junctions throughout the room need protection, usually with a membrane upturn behind the skirting tile.
• Areas around baths, basins and other fixtures must be treated according to their exposure to water.
• Penetrations such as taps and shower outlets must be sealed.
• Floor wastes must be fitted with puddle flanges to collect water that enters the screed.

The Standard was updated in 2021 with greater emphasis on falls, waterstops and drainage of the tile bed. Victorian building regulations reference it, and work must comply.

Our waterproofing process

1. Substrate preparation

A membrane is only as good as the surface it is applied to. We make sure the walls and floor are sound, clean, dry and fixed correctly. Wet-area rated sheeting must be screwed at the right spacing, joints must be treated and any movement in the floor must be addressed before waterproofing begins.

2. Priming

Most membrane systems require a primer that helps the membrane bond to the substrate. We use the primer specified by the membrane manufacturer.

3. Bond breakers

Where walls meet floors and walls meet walls, buildings move slightly. If the membrane is bonded rigidly across these junctions, movement can split it. Bond breakers, either a flexible sealant bead or a specialised tape, let the membrane flex at these points.

4. Puddle flanges and waterstops

A puddle flange is fitted around each floor waste so water that soaks into the tile bed is collected and directed into the drain. Waterstops are installed at shower entries and doorways where required, preventing water from travelling beneath the tiles into other parts of the house.

5. Penetration sealing

Every pipe and fitting that passes through the membrane, such as taps, shower outlets and spouts, is sealed with collars or appropriate sealant.

6. Membrane application

The membrane is applied in the number of coats and to the thickness specified by the manufacturer. Reinforcing fabric is used where required at junctions and corners.

7. Curing

Each coat must cure before the next is applied, and the full membrane must cure before tiling begins. Rushing this step is one of the most common causes of failure. We allow the full cure time, even when it means waiting an extra day.

8. Documentation

We photograph the membrane before tiling and provide documentation that records the system used and the areas treated.

Liquid and sheet membranes

There are two broad types of membrane used in bathrooms.

Liquid membranes are brushed or rolled on and cure to form a continuous, seamless layer. They suit most bathrooms, adapt easily to corners and penetrations, and are widely used. They rely on achieving the correct thickness and allowing proper curing.

Sheet membranes are factory-made sheets bonded to the substrate with adhesive, with overlapping seams sealed. They offer consistent thickness and can allow faster tiling, but require careful detailing at joints and corners.

We choose the system that best suits the substrate, the design and the conditions of each project.

Falls and drainage: the partner of the membrane

A membrane stops water from escaping, but it works best when water is moved quickly to the drain. That is the job of the floor falls. In a shower, the floor must slope consistently towards the waste so water never sits in corners or against the screen. Outside the shower, a gentle fall towards a floor waste means a spill or overflow drains away rather than spreading towards the door. The 2021 update to AS 3740 placed stronger emphasis on falls and on draining the tile bed itself, because water that soaks into mortar beneath tiles needs a path out. Without that path, mortar stays saturated, grout darkens and the membrane is placed under constant pressure. We set falls carefully with screeds shaped to the waste position, check them before tiling, and make sure the puddle flange sits at the right level to collect water from the bed.

Cold weather and curing in Gippsland

Warragul’s climate is cool and damp for much of the year, and that affects waterproofing. Many membrane systems cure more slowly in low temperatures and high humidity, and some cannot be applied below a minimum temperature. Rushing a membrane in winter, or tiling over one that is still soft, is a common cause of failure. We monitor conditions, use heaters or ventilation where appropriate and allow the full cure time stated by the manufacturer. This sometimes adds a day or two to the program in the colder months. It is time well spent, because a properly cured membrane is the foundation of a bathroom that stays sound for decades.

Waterproofing outside the shower

The shower attracts most attention, but other parts of the room need protection too. Around a freestanding bath, splashes and drips land on the floor every time it is used. Behind a basin or vanity, water runs down the wall and collects at the base. At the bathroom door, water tracked out of the room can wick into timber flooring next door. We treat these areas according to the Standard and the layout, so the whole room is protected rather than just the shower.

Timber floors and waterproofing

Many older homes in Warragul have bathrooms on timber floors supported by stumps. Timber moves with changes in moisture and temperature, which places extra demands on a waterproofing system. We assess the floor structure, stiffen it where needed, use suitable sheet flooring and choose membranes and details that tolerate movement. Getting falls right on a timber floor also takes care, especially where a low or level entry is wanted.

Concrete slabs and waterproofing

On concrete slabs, common in newer Warragul homes, the membrane is usually applied over the slab or over the screed, depending on the system. Recessed slabs allow level-entry showers. We check for cracks, moisture and level before waterproofing begins.

Signs your waterproofing may have failed

• Grout that stays dark or damp long after showering.
• Loose, drummy or cracked tiles, especially around the shower.
• Swollen or stained skirting boards, door frames or vanity bases.
• Mould or peeling paint on the other side of a shower wall.
• Musty smells that do not go away.
• Damp patches or stains on ceilings below an upstairs bathroom.
• Lifting floor coverings in rooms beside the bathroom.
• Soft or springy floor near the shower.

If you notice these signs, it is worth having the bathroom assessed. Sometimes the problem is failed grout or silicone, which can be repaired without major work. Often, especially in older bathrooms, the membrane itself has failed or was never there.

Why waterproofing fails

Common causes of failure include:

• Membrane applied too thin or unevenly.
• Inadequate curing before tiling.
• Missing or poorly installed bond breakers at junctions.
• No puddle flange at the floor waste.
• Penetrations left unsealed.
• Substrates that were not fixed or prepared properly.
• Floors without adequate falls, leaving water ponding against walls.
• Movement in timber floors that cracks rigid membranes.
• No membrane at all in older bathrooms.

Each of these is avoidable with care and correct procedure.

Waterproofing as part of every renovation

We do not treat waterproofing as an optional extra. It is part of every bathroom, ensuite, laundry and shower conversion we build. When we provide a scope, the membrane system, the areas treated and the curing time are all described clearly.

Repairing leaking showers

If your shower is leaking, the right fix depends on the cause. Where grout and silicone have failed but the membrane is sound, regrouting and resealing may solve the problem. Where the membrane has failed, the shower needs to be stripped back, any damaged structure repaired and a new membrane installed before retiling. We assess the shower carefully and explain the options honestly. Our resealing and grout services are described on separate pages.

The Victorian context

In Victoria, waterproofing of wet areas is part of building work regulated under state building regulations. Larger projects may require a building permit and domestic building insurance. Plumbing work associated with wastes and fixtures must be carried out by licensed plumbers. We explain what applies to your project before work begins and provide documentation at handover.

Common questions

How long does waterproofing take to cure?

It depends on the membrane system, the temperature and humidity. In Warragul’s cooler months, curing can take longer. We follow the manufacturer’s requirements and do not tile until the membrane is fully cured.

Can you waterproof over existing tiles?

Applying a membrane over existing tiles is not a reliable solution for a shower that is leaking through a failed membrane. A proper repair involves removing the tiles and installing a new membrane.

Does the whole bathroom floor need waterproofing?

It depends on the floor material, whether there is a floor waste and the layout of the room. AS 3740 sets out the requirements. Many bathrooms benefit from full floor waterproofing.

Will I get documentation?

Yes. We photograph the membrane before tiling and provide records of the system used.

Book a design consultation

Whether you are planning a renovation or worried about a leaking shower, book a design consultation. We will assess the room and explain how we would waterproof it properly.

Areas we service

• Bathroom Renovations Brandy Creek
• Bathroom Renovations Buln Buln
• Bathroom Renovations Bunyip
• Bathroom Renovations Darnum
• Bathroom Renovations Drouin South
• Bathroom Renovations Drouin
• Bathroom Renovations Jindivick
• Bathroom Renovations Labertouche
• Bathroom Renovations Longwarry
• Bathroom Renovations Neerim South
• Bathroom Renovations Nilma
• Bathroom Renovations Trafalgar
• Bathroom Renovations Warragul
• Bathroom Renovations Yarragon