Waterproofing

The part of the bathroom you never see

Ask anyone what makes a good bathroom and they will usually talk about tiles, tapware or the size of the shower. Ask anyone who repairs bathrooms and they will talk about waterproofing. The membrane beneath the tiles is the single most important part of any wet area. When it is right, the room can last for decades. When it is wrong, everything built on top of it eventually fails.

Every wet area we build in Drouin and the surrounding towns is waterproofed to the Australian Standard AS 3740, Waterproofing of domestic wet areas. This page explains what that involves and why we take it so seriously.

Why tiles and grout are not enough

It is a common belief that tiles keep water out. They do not. Grout is porous, and water passes through it every time the shower runs. Tiles themselves can crack, and adhesive does not stop water. Water that passes through tiles and grout must be stopped by a waterproof layer beneath, then directed to the floor waste. Without that layer, water soaks into screed, sheeting, timber framing and concrete, leading to rot, mould, rising damp, termite attraction and damage to adjoining rooms.

What AS 3740 covers

AS 3740 sets out the requirements for waterproofing wet areas in homes, including bathrooms, ensuites, laundries and toilets. In simple terms it covers:

• Which surfaces must be waterproof, such as shower floors and walls within the shower area.
• Which surfaces must be water resistant, such as bathroom floors outside the shower and walls near baths and basins.
• How junctions between walls and floors, and between walls, are treated so the membrane can accommodate movement.
• How penetrations, such as taps, shower arms and wastes, are sealed.
• How floor wastes connect to the membrane.
• How thresholds and doorways are detailed so water stays in the wet area.
• How membranes are installed and cured.

We apply these requirements in every bathroom, ensuite and laundry we build, and often exceed them, for example by waterproofing the whole bathroom floor rather than only the minimum areas.

Our waterproofing process

1. Preparing the substrate

Membranes need a clean, sound, dry surface. We check that sheeting is fixed correctly, that screeds are cured and that surfaces are free of dust and contaminants. Any gaps are filled and edges are prepared.

2. Screeding to fall

Before waterproofing a shower floor, we create falls so water flows to the waste. Depending on the system, the membrane may be applied below or above the screed. Either way, the finished floor must drain freely.

3. Priming

A primer suited to the substrate and membrane is applied so the membrane bonds properly.

4. Bond breakers and junction treatment

At every wall-to-floor and wall-to-wall junction, a bond breaker is installed. This allows the membrane to stretch slightly across the junction as the building moves, rather than tearing. Movement at junctions is normal in all buildings, so this detail is essential.

5. Puddle flanges and penetrations

A puddle flange is fitted at each floor waste so the membrane can be dressed into it, directing water into the drain rather than around the outside of the pipe. Penetrations for taps, shower arms and outlets are sealed with suitable collars or sealants.

6. Reinforcement

At corners, junctions and other high-stress points, reinforcing fabric or tape is embedded in the membrane to strengthen it.

7. Applying the membrane

The membrane is applied in the number of coats required by the manufacturer, to the specified thickness, and carried to the required heights on walls and across thresholds. Each coat is allowed to dry before the next.

8. Curing

The membrane must cure fully before tiling. Cure times depend on the product, temperature and humidity. In a Drouin winter, cold, damp conditions can lengthen cure times considerably. We never tile over a membrane that has not cured, because that is one of the most common causes of failure.

9. Inspection and photographs

Before tiling, we inspect the membrane for coverage, thickness and detailing, and photograph it. These photographs are given to you at handover as a record of the hidden work.

Types of membranes

There are several kinds of waterproofing membranes used in domestic wet areas:

• Liquid-applied membranes, painted or rolled onto surfaces, cure to form a continuous flexible layer. These are the most common in bathroom renovations.
• Sheet membranes, supplied in rolls and bonded to surfaces, offer consistent thickness.
• Combined systems, which use sheet materials at junctions with liquid membranes elsewhere.

The right choice depends on the room, substrate and tiles. We select systems that suit each job and install them to the manufacturer’s instructions and AS 3740.

Laundries and toilets

Waterproofing requirements are not limited to showers. Laundries and toilets with floor wastes are wet areas, and their floors and certain wall areas require water resistance or waterproofing. We apply the same care in these rooms.

Waterproofing timber floors

Many older homes in Drouin have timber floors. Before waterproofing, we confirm that the floor is stiff and sound, replace any damaged boards or joists and install a stable substrate such as compressed fibre cement sheet. A membrane over a moving floor will eventually crack, so this preparation is essential.

Waterproofing concrete slabs

Newer homes and some older homes have concrete slabs. Slabs may need grinding, levelling or preparation before waterproofing. If the slab has been recessed to allow a level shower entry, falls and membrane details must suit the recess.

Signs of failed waterproofing

• Loose or drummy tiles.
• Cracked, crumbling or discoloured grout.
• Swelling or staining of skirtings, door frames and joinery.
• Mould on walls or ceilings near the bathroom.
• Water stains on ceilings below.
• Damp carpet in adjoining rooms.

If you notice these signs, see our leaking shower repairs page.

Compliance and documentation

Waterproofing is a regulated part of building work in Victoria. We install waterproofing to AS 3740 and provide photographs of the membrane at handover. Where required, documentation is provided with the other compliance certificates for your bathroom.

Doorways and thresholds

One of the most overlooked waterproofing details is the doorway. If the bathroom floor is level with the hallway and water escapes the shower, it can track straight under the door and into carpet or floorboards. AS 3740 sets requirements for how water is contained at the entrance to a wet area. In practice, this may involve a waterstop angle beneath the tiles at the doorway, with the membrane dressed up against it, combined with floor falls that keep water moving towards the waste rather than the door. Where a level threshold is wanted for accessibility, the detailing is particularly important, and we plan it carefully at the design stage.

Niches, seats and screens

Recessed shower niches and built-in seats add convenience but also create extra corners and edges where membranes can fail. Every internal corner in a niche receives a bond breaker and reinforcement, and the base of the niche is sloped slightly so water does not sit on it. Screen fixings are another risk: drilling through tiles also drills through the membrane beneath, so holes must be sealed properly. Where we can, we plan screen positions so fixings sit into solid noggins and are sealed as they go in.

Weather and timing in Gippsland

West Gippsland winters are cool and damp, and that affects how long membranes, screeds and adhesives take to cure. A membrane that might be ready for tiling in a day or two in summer can need noticeably longer in July. Rather than rushing, we build realistic cure times into the schedule and, where conditions allow, use ventilation to help. The few extra days are always worth it.

Common questions about waterproofing

Can I waterproof over old tiles? Not as a reliable long-term repair. Membranes must be applied to sound, prepared substrates.

How long do membranes take to cure? It depends on the product and conditions. We follow the manufacturer’s instructions and allow extra time in cold weather.

Does the whole bathroom floor need waterproofing? AS 3740 sets minimum areas. We often waterproof the whole floor for extra protection.

How long should a membrane last? A properly installed membrane, protected by tiles and maintained grout and sealant, should last for the life of the bathroom.

Book a design consultation

Waterproofing is the foundation of every bathroom we build. If you are planning a renovation or concerned about an existing wet area in Drouin or nearby, book a design consultation and we will explain how we would approach your room.

Areas we service

• Buln Buln
• Bunyip
• Darnum
• Drouin South
• Drouin West
• Drouin
• Garfield
• Jindivick
• Labertouche
• Longwarry
• Nar Nar Goon
• Neerim South
• Tynong
• Warragul