How to Waterproof a Bathroom

Bathroom with a white tub, a red colored carpet, two small white flower pots with green plants near the mirror & a big white flower pot on the floor.

According to the Australian Master Tilers Association (AMTA), faulty waterproofing is among the top three building defects in Australia and can cause as much structural damage to a house as termites. Waterproofing is a fundamental and vital construction activity to maintain the integrity of both commercial and residential buildings over their service life. It minimises the post-completion problems mainly caused by water damages such as mould growth and rusting.

What is waterproofing?

This method prevents water from penetrating into a room. Also, it helps keep the space dry. Therefore, it also minimises the post-completion problems mainly caused by water damages such as mould growth and rusting.

Wet areas in a building are the spaces containing sanitary fixtures and appliances which are subject to high levels of moisture from direct wetting, condensation and high humidity levels.

Of all the rooms in your house, you will need the bathroom to be the most waterproof. Waterproofing is one of the first steps to take place when a bathroom is being built.

Australian waterproofing regulations

There are regulations in place that your waterproofing will need to comply with, as set out by the Building Code of Australia and Australian Standards (AS 3740-1994), which stipulates that:

  • Shower floors must be totally waterproofed and shower walls must be waterproofed up to a height of 1,800 mm.
  • Bathroom walls must be waterproofed up to a height of 150 mm.
  • The step down from the shower to the floor must be waterproofed to a height of at least 100 mm.
  • If the bathroom is not on the ground floor, the entire bathroom floor must be waterproofed.
  • If the bathroom floor contains any wood, the entire bathroom floor must be waterproofed.

Different types of waterproofing

Cementitious waterproofing

Probably the easiest waterproofing materials to use. They’re readily available. They’re easy to mix and apply. They give better bonding and a more solid, durable coating.

Liquid waterproofing membrane

Involves the application of a specialist liquid roof coating. The coating cures to form a rubber-like elastomeric waterproof membrane, capable of stretching and returning to its original shape without damage. A cost-effective method that can deliver up to 25 years of performance depending on the coating system employed.

Bituminous waterproofing

Designed to protect residential and commercial buildings. Bitumen is a mixed substance made up of organic liquids that are highly sticky, viscous, and waterproof.

Bituminous Coating Waterproofing Method

Used for waterproofing and a flexible protective coating. It is an excellent protective coating and waterproofing agent, especially on surfaces such as concrete foundations.

Bituminous Membrane Waterproofing Method

A popular method used for low-sloped roofs due to their proven performance.

Polyurethane Waterproofing

Polyurethane is made up of two components, base and reactor. A liquid coating for waterproofing applications. A popular choice due to its ease of installation. It is easy to install, provides a seamless finish and have long term durability and wear resistance.

Why is waterproofing so important?

A waterproofing system provides protection to the structure from water ingress. The practice of waterproofing dates back to the ages where the different techniques used were bituminous, metallic sheet, polyurethane-based and so on.

Proper waterproofing in wet areas is absolutely important– water leaking into the floor and wall spaces can very easily rot structural timbers and do some heartbreaking damage to any building or house. The worst bit about this kind of damage is that you won’t normally realise it’s happening until the worst of the damage has already been done.

If a wet area is not waterproofed or is not waterproofed correctly, water can seep out undetected into other areas of the home. This can cause:

  • Rising damp: where water rises up through walls, floors and masonry via capillary action, in opposition to gravity.
  • Mould and mildew: can release spores into the air which can be harmful to those with respiratory problems such as asthma.
  • Corrosion of plumbing: rusted pipes can lead to further water leaks.
  • Concrete cancer: the steel reinforcing within the concrete begins to rust, causing it to expand and displace the concrete around it, which makes it become brittle and cracked and weakens the building’s foundations.
  • Warping and rotting of structural timbers: if major structural components such as bearers, joists, posts, and beams are compromised, the integrity of the entire house can be put in jeopardy.
  • Compromised electrics: water dripping onto light fittings and pooling in ceilings can create a high risk of fire or electrocution.

How to waterproof a bathroom

Generally, waterproofing is one of the first processes when building a bathroom as it involves installing a barrier around the walls and floor. Like any part of the construction process, preparation is essential.

Bathroom waterproofing is applied before tiles are laid, using a combination of sheet and paint-on liquid membranes. Two coats are needed, each taking 24 hours to dry. The extra sealant may also be needed once the tiles are down. It's a job that can take up to four days. This work should only be carried out by a licensed tradesperson such as a builder, tiler or licensed waterproofing expert.

Waterproofing is one area that needs to be done right to avoid serious long term damage to your commercial and residential building and before deciding to do it yourself, you should consider the impact unlicensed work might have on your home or commercial insurance.

If waterproofing isn’t completed correctly, it can be catastrophic for your home. For example, if a first-floor bathroom starts to leak into lower living areas, it can cause damage to the electrical wiring, plastering on the ceiling and furniture and flooring on the lower floors.

Common mistakes in waterproofing

  • Choosing the wrong waterproofing material: each one of the available waterproofing materials has a specific use case.
  • Faulty External Plastering: if the external plastering of the building envelope is carelessly done, it could result in ingress points for water.
  • Lack of Preparatory Work: preparing for waterproofing is almost as important as the task itself. It involves cleaning the surface to remove dust, filling all the holes, cracks and cavities, repairing the damaged sections, relocating the embedded pipes, among others.
  • Incorrect Diagnosis of a Leakage: if leakage is detected during waterproofing, it is crucial to analyse it correctly. The source of the leakage is not always located near its visual marks.