A Guide to Expertly Waterproofing Your Bathroom

Projex - Guide to Expertly Waterproofing Your Bathroom

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. This article looks at what waterproofing is, why it’s essential to have, how it’s applied and why it should be left to the experts.

What is waterproofing?

Unlike a ‘water resistant’ material which restricts the movement of moisture, a ‘waterproof’ material is one that doesn’t allow moisture to pass through it at all.

In wet areas of your home, waterproofing involves the application of a suitable membrane product to make sure no moisture can escape from the wet areas into other parts of the home.

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

Waterproofing is normally required anywhere there is a water outlet including bathrooms, showers and baths in particular, laundries and kitchen wet areas.

Costs vary depending on the size of the room and type of waterproofing used, but you can expect to pay anywhere between $35 – $300 per square metre or $500 to $4000 in total to waterproof an average sized bathroom.

History of waterproofing

It may surprise you to learn that waterproofing has been part of human construction for more than 13,000 years and is considered the third oldest trade behind carpenters and masons.

Back in the days of hunter-gatherers, waterproofing was used to prevent stored produce from being spoiled by the weather and to seal primitive boats using a bitumen emulsion.

Bitumen waterproofing was also used in the Egyptian pyramids to keep the tombs of the Pharaohs dry when the Nile flooded its banks every year. So it has played an important role over a long period of time and has now become an integral part of modern building techniques.

Australian waterproofing regulations

Regulations vary from state to state in Australia, but as a general rule, waterproofing needs to be applied in accordance with the Building Code of Australia (BCA) and the Australian Standards (AS 3740-1994), which stipulate 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

Waterproofing membrane products come in a variety of different styles. Some are rubber sheets that are rolled out and attached to the surface, while others come in liquid form and are applied with a brush or roller. The most popular kind used in bathrooms today is a liquid membrane, which has the advantage of being highly flexible and relatively easy to install.

The CSIRO has developed a classification system for membranes, based on their ability to stretch before breaking. The classifications are:

  • Class 1 – stretches to a length 65% more than its original length. Examples include fibreglass, metal and water based epoxies.
  • Class 2 – stretches between 65% and 200% more than its original length. Examples include acrylic membranes and bitumen based membranes.
  • Class 3 – stretches over 200% more than its original length. Examples include water based polyurethane, solvent based polyurethane, sheet rubber, and PVC sheet membranes.

Why is waterproofing necessary?

Water can do a lot of damage in a residential building, particularly when it goes undetected for a long period of time. 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 – these can release spores into the air which can be harmful to those with respiratory problems such as asthma.
  • 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.
  • Corrosion of plumbing – rusted pipes can lead to further water leaks, compounding the problem even further.
  • Compromised electrics – water dripping onto light fittings and pooling in ceilings can create a high risk of fire or electrocution.
  • 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.

Waterproofing wet areas such as bathrooms:

  • Stops leaks – provides a watertight seal that will prevent water leaking through any cracks /gaps in floors and walls, which in turn can save structural repairs down the track.
  • Prevents damp and mould – adds a waterproof barrier which prevents the build-up of condensation and damp under tiles, which can penetrate wood, plaster and brickwork.
  • Provides insulation – waterproofing walls helps to keep the warmth in and reduce household heating costs in winter.
  • Increases your property value – a fully tanked bathroom adds value to your property, just as a badly waterproofed one will detract from the value and deter potential buyers.

Who should waterproof your bathroom?

While this article includes the basic steps involved in waterproofing a bathroom, it should be pointed out that in some states of Australia, this work can only be carried out by a licensed tradesperson such as a builder, tiler or licensed waterproofing expert.

In New South Wales and Victoria the waterproofing contractor must provide certification for the works. In other states and territories the person who carries out the work must provide written assurances that it has been done in accordance with the Australian Standard AS3740-2010 – (waterproofing of domestic wet areas).

The waterproofing membrane used must be compatible with the substrate and adhesive, curing times must be accurate and products should comply with the Plumbing Code of Australia and Australian Standards regulating product quality.

Waterproofing is one area that needs to be done right to avoid serious long term damage to your home and before deciding to do it yourself, you should consider the impact unlicensed work might have on your home insurance, should you need to make a claim further down the track.

What are the main causes of faulty waterproofing?

Poor workmanship is the number one cause of waterproofing failures and includes:

  • Poor preparation – unless the surface to be waterproofed is free from dust and dirt, the membrane will not bond properly to it and will eventually peel off.
  • Poor application – the membrane needs to extend beyond the wet area, every millimetre must be covered & it must be installed to manufacturers recommendations
  • Cheap waterproofing product – a good quality waterproofing product must be used, as a low quality membrane can fail.

How long does waterproofing last?

A quality waterproofing sheet membrane professionally installed should last for a very long time. Most waterproofing products come with a minimum 7 year warranty but correctly applied (pending on which membrane is chosen), a membrane should last much longer than that.

Signs that your bathroom may have developed a leak can include swelling skirting boards, peeling paint, mouldy cupboards, ceilings and walls and stained timber under the subfloor.

You can attempt to fix a bathroom leak using an over the counter silicone sealer, but this will only be a stop gap solution, as these products usually only target one area of the shower or bath, tend to go mouldy fairly quickly and will not withstand continued building movement.

The only long term solution is to remove the tiles and replace the waterproofing membrane altogether, which reinforces the argument for using the best quality membrane in the first place and having it professionally installed by an expert to ensure the greatest possible longevity.

Because of the damage poor waterproofing can create and the number of cases where shoddy workmanship is at fault, organisations such as the Australian Master Tilers Association (AMTA) are now campaigning for more regulation of the waterproofing industry in Australia.

Therefore, to ensure your waterproofing is installed correctly, it is highly recommended that you use an accredited and licensed tradesperson, because even if your local state regulations allow you to do the work yourself, it can still be a messy and costly experience.

And if you do it wrong, it can lead to all kinds of problems that you may not discover for years to come and which could end up costing you much more to fix than the few dollars you saved by going down the DIY path.

For more information on internal waterproofing, we suggest the Internal Wet Area Waterproofing Book 1, from the Master Builder Association.