Wet Areas

Poor wet area design or installation can compromise safety, comfort and convenience for building users, and lead to significant structural damage.

Wet area wall and ceiling linings and finishes

A wide range of wet areas flooring and floor finishes is available, each with pros and cons.

On this page:

  • Code requirements
  • Timber boards
  • Plywood
  • Particleboard and MDF
  • Compressed sheet
  • Sheet vinyl
  • Ceramic and stone tiles
  • Ceramic-based solid plaster and concrete
  • Cork tiles
  • Monolithic applied coatings
  • Plasterboard sheet linings
  • Vinyl and vinyl-coated wallpaper
  • Paint and clear finishes
  • Decorative panels

Code requirements

In accordance with NZBC clause E3 Internal moisture, wall linings and finishes exposed to water splash must be impervious and easy to clean.

Acceptable Solution E3/AS1 lists suitable linings and finishes for wet areas as:

  • timber and timber-based materials (such as timber boards, plywood, particleboard, MDF or compressed sheet) if sealed with a waterproof applied coating
  • waterproof sheet material such as vinyl
  • ceramic and stone tiles with 6% maximum absorption (joints must be waterproof and bedding material specified as suitable for wet area use)
  • cement-based solid plaster and concrete with steel trowel or polished finish
  • cork tile or sheet with a waterproof coating and sealed joints
  • monolithic applied coatings (e.g. terrazzo) with a polished, non-absorbent finish
  • sheet materials (e.g. plasterboard) with vinyl-coated wallpaper or semi-gloss or gloss paint finishes
  • water-resistant sheet linings with decorative, high-pressure laminate or factory-applied polyurethane or resin finishes
  • modular lining units that are impervious and are easy to clean.

E3/AS1 specifically excludes the use of the following in showers:

  • Cork tile or sheet with a waterproof applied coating.
  • Sheet materials (e.g. plasterboard) with vinyl-coated wallpaper or semi-gloss or gloss finish.
  • Ceramic and stone tiles that have not been laid over a continuous, waterproof membrane.

See Quick reference guide for wet area wall finishes.

Other wet area wall linings that are not listed in E3/AS1 (so must be consented as an Alternative Solution) include:

  • profiled and sheet metals (provided the material has an air barrier behind it to prevent moisture migrating into the framing behind)
  • acrylic panels
  • polyurethane and epoxy-based coating systems.

Timber boards

Timber has been commonly used in wet areas since the opening years of the 20th Century and is permitted under E3/AS1 if finished with a waterproof applied coating. Timber is not suitable for shower areas.

An impervious finish can be a minimum of three coats of semi-gloss or full-gloss paint (oiled finishes are not recommended in wet areas). Timber should also be sealed or primed on the edges and back face before installation

Timber is dimensionally unstable and susceptible to moisture. Movement of the timber may crack an applied finish, allowing moisture ingress that can lead to swelling, staining and premature coating deterioration. If untreated, timber is also more susceptible to borer attack.

Plywood

Plywood is not commonly used as a wall lining in wet areas, but it is more stable than timber and wood-based products. It can be treated, but treatment must be compatible with waterproofing membranes or coatings applied and should be a water-based preservative such as CCA (LOSP is not suitable because of the solvents used). It has a high resistance to impact, is a suitable substrate for tiling and may be used in water splash areas if it has an appropriate finish. It is not suitable as an exposed finish in showers.

Plywood must:

  • be a minimum of 9 mm thick
  • have edges sealed prior to installation
  • have a minimum of three coats of water- or oil-based, semi-gloss or full-gloss paint (oiled finishes are not recommended in wet areas).

Particleboard and MDF

Particleboard and MDF are not generally recommended as wet area wall linings, as they are very easily damaged by moisture. They are permitted to be used in water splash areas under E3/AS1 if they:

  • have a waterproof applied finish
  • are finished with a decorative wood veneer with a waterproof applied finish
  • have sealed edges and back faces prior to installation.

Compressed sheet

Compressed sheet is commonly used as a substrate for a tiled finish. It is very stable but must remain dry. It may also be finished with vinyl wallpaper or wall covering. A paint finish is not a suitable finish for compressed sheet lining.

Sheet vinyl

Sheet vinyl has excellent resistance to water and is suitable for use in showers (open showers). It must be laid over a rigid substrate such as concrete, particleboard, plywood or compressed sheet and requires heat- or solvent-welded joints to be fully watertight. Sheet vinyl for wall coverings is typically around 1 mm thick. It is not generally used for ceiling lining.

Ceramic and stone tiles

Ceramic and stone tiles are popular finishes for wet areas and for showers in particular. They must have 6% maximum water absorption, and glazed tiles should have glazed edges. A tiled finish for a splash zone under E3/AS1 requires:

  • waterproof grout joints
  • a firm, stable, rigid substrate such as concrete, plywood or fibre-cement sheet
  • flexible (mould inhibiting sealant) movement joints at the floor/wall and wall/wall junctions

In showers, a waterproof membrane laid underneath the tiles in accordance with AS/NZS 4858:2004 Wet area membranes is required.

BRANZ recommends waterproofing membranes be installed under tiles on surfaces that are vulnerable to wetting, whether or not required by E3/AS1.

Cement-based solid plaster and concrete

Cement-based plaster to concrete walls can provide a suitable lining if it has a steel trowelled or polished finish, or has a semi-gloss or gloss paint finish.

Cork tiles

Cork tiles must be laid over a rigid sheet lining substrate. They are not usually used for ceilings and are not suitable for shower areas as they absorb water when wet. They are permitted to be used in water splash areas under E3/AS1 if they have a waterproof applied finish.

Monolithic applied coatings

Terrazzo with marble or stone aggregate can be ground to a hard-wearing finish. Prefabricated terrazzo panels may also be used for partitions or screens.

Plasterboard sheet lining

Plasterboard is a commonly used wall and ceiling lining, and water-resistant grades are available for use in wet areas. It can be applied directly to timber or steel framing, or to strapped concrete or concrete masonry walls. It must be protected from direct wetting.

Water-resistant plasterboard must be protected by a waterproofing system when used as a substrate for tiling in a shower or other high risk areas such as around the bath and hand basin. BRANZ recommends protecting plasterboard behind tiles with a waterproof membrane in all water splash areas.

Standard grade plasterboard is suitable for areas that are normally dry or subject to occasional splashing. An oil-based sealer coat and a minimum of three coats of water- or oil-based, semi-gloss or full-gloss paint should be used.

Plasterboard should be stopped to level 4 or 5 for a paint finish, and level 3 for a flexible sheet or tiled finish.

Vinyl-coated wallpaper

Vinyl-coated wallpaper may lose adhesion at joints in high levels of moisture so should only be used in areas that have minimal wetting. A plasterboard flush-stopped finish must be to at least level 3, or an equivalent finish for fibre-cement sheet, as imperfections may be visible in the substrate.

Plasterboard and cement-fibre sheet substrates require sealing with a water-resistant sealer before applying vinyl-coated wallpaper.

Paint and clear finishes

Paints and clear finishes should not be used on surfaces that are continually wet. In areas where occasional wetting occurs in well-ventilated kitchens and bathrooms, water-based acrylic enamel paint applied over a solvent-based sealer coat is generally satisfactory. The ability to withstand moisture is better if water-resistant grade plasterboard is used.

High-gloss coatings should be used in areas of high wear and where regular cleaning is required. Semi-gloss coatings may be used in areas of low wearing or wetting. Matt finish coatings should only be used in dry areas.

In comparison to semi-gloss and matt-finish coatings, high-gloss coatings:

  • are generally more durable
  • have a higher resistance to abrasion and staining
  • tend to highlight substrate imperfections
  • increase glare and diffuse light less
  • are easier to clean
  • are less affected by mould growth.

Decorative panels

A range of factory-finished, wood-fibre or fibre-cement panels are available as wet area linings including within showers. Finishes include:

  • high-pressure laminate comprising multiple layers of kraft paper impregnated with phenolic resin on hardboard, particleboard and MDF
  • factory-applied polyurethane coating on fibre-cement or hardboard.

Low pressure melamine laminate on hardboard is not suitable for wet zones and splash areas.

Pre-finished panels have visible joints connected by aluminium or PVC jointer sections. Bottom edges must be separated from the floor or shower by a gap, and edges must be sealed before installation.


Updated: 22 August 2013