Consumer Advice


Consumer Advice

Tiled Shower Construction

Leaking tiled showers are very common throughout New Zealand. Leaking can occur in both concrete and timber constructed homes. All buildings, timber or concrete or a combination of both, move with atmospheric conditions and ground expansion / contraction. As a result many paint-on waterproof coatings crack as they are not pliable enough to cope with such movement. Even a seemingly-solid concrete floor can crack causing waterproofing membrane failure, allowing water into the building’s construction with the long-term result being rotted flooring, framing, carpets, etc. Even for proficient, experienced applicators, the performance of a waterproof membrane over an extended period of time is very often beyond their control. For the long-term, only a true one-piece shower base / tray with actual sides can reliably contain water.

Tiled Shower Construction Methods

1. Concrete Plaster — Forming of a tile shower base with a concrete plaster is a common method. Even for experienced tradesmen, achieving the desired results involves a lot of time and skill. If the base is not formed correctly there can be ‘ponding’ of water causing mould and possible breakdown of the tile adhesive due to constant immersion.

Concrete-plaster mixes are generally quite weak and can crack causing catastrophic cracking of paint-on waterproofing. Excessive structural movement of the substrate can also cause a plaster base to crack and split paint-on membranes..

2. High-Density Foam Bases — A pre-shaped foam board can be utilised to provide the drainage slope required. However, if not glued adequately, movement of the base and joins can result in cracking of the waterproofing membrane and tiles.

3. Shaping of Timber Floor — Timber floor joists can be shaped to the drainage slope required and covered with plywood or compressed fibre-cement sheet. Any substantial floor movement will result in cracking or tearing of many waterproofing membranes.

Waterproofing Membrane Products and Problems

Acrylic Paint-on Membranes — Mostly a 2 or 3 coat paint-on application. The coatings can be applied without enough coverage over reinforcing materials with pin-holes not apparent to the naked-eye allowing water to escape to the building structure. The application of tiles and the required cement-based adhesives before the paint-on membrane has fully cured can result in the membrane re-emulsifying creating a leaky shower. Acrylic coatings are not very pliable and over time they become brittle and are prone to cracking. The membrane will often crack from building movement caused by changing atmospheric conditions.

Fibre-Glass Waterproofing — These membranes are too rigid and stress cracks can occur to building movement and cracking concrete floors. The resins do not adhere will to plastic waste-flanges and water can seep between the two, back up under the membrane and into the timber floor substate.

Sheet Membranes — Rubber sheet membranes require adhesives at their joins and these will break down over time with a resulting leaky shower.

Fibre-Glass Shower Tray / Base — These can be subject to osmosis (a common problem with fibreglass boats) where moisture seeps through the gel-coat surface into the reinforcement and eventually onto the bathroom flooring and timber framing.

Tilers and Waterproofing

To comply with the New Zealand Building Code all waterproofing is to be performed under licence issued by the waterproof coating manufacturer and/ or agents. Beware, there are tilers applying waterproofing without any training or approval by a manufacturer. With some brands of waterproofing there is not a lot of policing of the product application. We, as tile shower base suppliers, often see tilers, novices and DIY homeowners easily purchasing and applying acrylic, cement/ latex, or urethane waterproof coatings without a licence or manufacturer’s oversight. Where a building consent has been issued for the construction of a new home or renovation of a bathroom, and before a Code of Compliance Certificate can be granted by the council, a licenced applicator must provide a producer statement and warranty statement for the product applied and the workmanship thereof. Impresa issues a warranty statement with each shower base, subject to its correct intended use. The shower base installer and the wall membrane applicator will respectively issue producer statements.

Impresa Tile Shower Trays

A one-piece shower tray / base is the true leakproof method for a shower base. Manufactured from an expoxy-coated marine-grade aluminium, it is unaffected by building movement, inexperienced or unskilled waterproofers / tilers, drying times, and on-site abuse by other sub-trades.

General Tiling Facts

Tile Installation and Adhesives

Not all tile adhesives are suitable for wet areas. Ensure the tile adhesive your tiler is proposing to use is compatible with constantly wet areas — see Approved Waterproofing and Adhesives. All tiling is to be in accordance with AS3958.1 and the BRANZ Tiling Good Practice Guide.

Ceramic and Porcelain Tile and Water Absorption

Ceramic tiles are manufactured from red or brown clay and most often a glaze is applied to the top surface. Porcelain is a general term. As with ceramic tiles, semi-vitrified porcelain tiles are porous, absorbing and allowing the passing of moisture to the substrate below — they offer no waterproofing and as such they are a covering only. A fully vitrified porcelain tile will not absorb water, however, water will pass through cement grout if installed between each tile.

Cement Grout Option

The cement grout commonly used between tiles is very absorbent, allowing water to pass through the substrate below. A grout penetrating sealer can be applied to temporarily prevent water absorption and the growth of mould, but it is not a long-term option, especially in a shower as over time the chemical structure of the sealer will break down. With cement grout it is imperative that it is cleaned regularly with a light bleach solution or similar commercial product.

Epoxy Grout Option

Epoxy grout is the best option in a tiled shower as being a non-absorbent material, it will not promote the growth of mould.