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Best practice for waterproofing in showers

Up to 90% of bathroom complaints relate to waterproofing and leakages. Shower areas are notorious for causing problems, and they require special attention to prevent water and moisture from oozing through the barriers to underlying concrete and metal frames, resulting in costly structural damage and disruptive repairs.

Let’s have a look at what’s changed in the NCC 2022* requirements for waterproofing showers.

*The NCC 2022 was adopted by the states and territories on 1 May 2023.

Walls in wet areas

Leakages do not only lead to deterioration in the appearance of the shower and surrounding areas, but also result in an unhealthy environment for occupants as they provide the perfect conditions for mould to flourish. Over time leakages will result in structural damage to the concrete and framing.

Surfaces in the shower area need to be impervious, easy to clean and prevent water from penetrating behind linings or into concealed spaces. (Note that the NCC definition of “shower area” is the area affected by water from a shower, including a shower over a bath.)

Having a fully tiled shower does not make it waterproof and does not comply with NCC 2022. Ceramic tiles may be waterproof, but cement-based grout is not, and waterproofing underneath the tiles is therefore not negotiable.

The NCC distinguishes between the use of waterproof and water-resistant materials in wet areas, and defines these properties as follows:

  • Waterproof means the property of a material that does not allow moisture to penetrate through it.
  • Water resistant means the property of a system or material that restricts moisture movement and will not degrade under conditions of moisture.

All building elements used in the shower area must comply with the revised AS 3740: 2021 - Waterproofing of domestic wet areas. From 1 May 2023 this standard is referenced in Volume 1 & 2 of the 2022 NCC, replacing the 2010 edition.

Waterproof membrane

To ensure proper waterproofing, a combination of several components is required to achieve a waterproof barrier, including a waterproof membrane, substrate bond breakers, sealants and finishes.

The waterproof membrane is a layer of material impervious to water that is usually applied as a liquid. It must comply with AS/NZS 4858:2004 Wet Area Membranes and be applied according to the manufacturer’s instructions.

Failure of the membrane is the biggest culprit in shower leakages. The major causes of membrane failure are:

  • No primer or improper installation and curing
  • Building movement, such as a timber floor or wall that move differently to bricks or concrete

The NCC previously required wet areas to have a waterproof membrane applied only at the wall and floor junctions and at the joints, but this has changed in NCC2022. The NCC 2022 requires that the entire water-resistant wall lining of a shower area (enclosed or unenclosed) must be waterproofed to a minimum height of 1800mm above the finished floor level or 50mm above the shower rose, whichever is highest.

At Siniat this has always been our recommendation, but it’s now an NCC2022 requirement.

The area that needs to be covered by the waterproof membrane further depends on the following:

  • Whether the shower is enclosed or unenclosed; and,
  • The substrate
External tray for enclosed shower on
timber flooring.
Waterproofing 2
Internal in situ tray for unenclosed shower
on concrete or compressed fibre cement floor.

Unenclosed shower areas are open on one or more sides. They extend 1500mm horizontally from the shower connection on the wall, up to a height of 1800mm from the finished floor.

Enclosed shower areas are bounded by walls or screens up to a height of 1800mm from the finished floor. Walls or screens include hinged or sliding doors that control the spread of water to within the enclosure. A shower fitted with a frameless glass shower screen or screen over a bath less than 1500mm long is not an enclosed shower.

Refer to the diagrams above or the Blueprint Technical Manual (3.4 Internal Wet Areas using Plasterboard) for more detail.

Water resistant substrates

Choosing a substrate material that effectively manages water and moisture is the first step in creating a bathroom that will remain waterproof for many years to come. Surface finishes like ceramic and porcelain tiles also require a stable, flat and flex-free substrate

Waterproofing of wet area walls may be achieved by using water-resistant plasterboard or fibre cement board for the substrate.

The HIA, Master Builders and BRANZ make no distinction between using fibre cement and specialty water resistant plasterboard in wet areas. Water-resistant plasterboard is known for its dimensional stability, good acoustic performance, light weight and ease of use in terms of handling and scoring.

The dimensional stability is one of the key benefits of choosing water-resistant plasterboard over fibre cement because fibre cement expands and contracts with humidity and shrinks over time. This leads to cracks in the cornice and, over time, cracks in the joints.

Plasterboard also has a smoother surface finish than fibre cement, and is therefore a better choice to avoid glancing light issues.

Siniat offers various specialty solutions for internal wet areas:

  • Watershield is a water-resistant plasterboard suitable for use in most internal wet areas and the perfect substrate for tiles.
  • Multishield offers the combined benefits and properties of fire, water and mould resistance.
  • If the shower is located in an area where high traffic is expected, such as public bathroom facilities or in a gym, impact resistant Trurock is an excellent choice. Trurock HD takes it even one step further and offers the added benefit of mould resistance and enhanced impact performance.

Choosing the best sealant

Waterproofing is a very black and white area: a room is either waterproof or it is not. Even the slightest crack or cavity can jeopardise all your efforts to prevent water from penetrating the underlying structures.

Choosing the best compounds for jointing and the final touches is therefore as important as all the other steps described above to create a waterproof system.

Siniat recommends using Mastabase or Mastalongset for all plasterboard joints, corners and fastener heads in the shower area.

No shortcuts

The NCC2022 requirements make it clear that there are no acceptable shortcuts when waterproofing a shower. Only by following the NCC requirements and best practice recommendations you can save yourself the costly headaches that may wait down the line.

To find out more about Siniat products, contact us online or call us on 1300 724 505.