A step-by-step guide to bathroom waterproofing for new Aussie homeowners

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worker waterproofing a bathroom

Picture this: you finally bought a house! But after a few months or years, you start seeing water stains on the ceiling or on the wall. Chances are, you forgot one of the most important aspects of maintaining a home: bathroom waterproofing. 

This process prevents excess moisture from accumulating inside floors and walls and causing severe structural damage. It also prevents mould and mildew from growing.

In this guide, we’ll talk about the benefits and the process of waterproofing a bathroom. We’ll also answer some of the most frequently asked questions on the topic.

Let’s begin!

applying waterproofing using brush

What is bathroom waterproofing?

Bathroom waterproofing involves installing a physical barrier to avoid leaks and moisture buildup inside a house or a building. Here are some of the areas you should waterproof:

Walls: The walls behind the shower need a waterproofing membrane underneath the finished wall. This prevents droplets from accumulating inside the wallboards. If your bathroom has porous tiles, make sure that the tiles are sealed.

Floors: The subfloor underneath tiles must be protected by a waterproofing membrane to keep moisture away. Also, remember to seal grout annually to prevent water from seeping through the cracks.

Ceilings: Use waterproof paint for your bathroom ceiling. 

Superdraft tip: Aside from bathrooms, wet areas in kitchens and laundry rooms need to be waterproofed.

modern bathroom design

Benefits of bathroom waterproofing

It’s important not to skip or delay waterproofing, especially if you’re planning a bathroom renovation. Leaving it off for later can cause several problems down the road. Here are some of the reasons you need to get your bathroom waterproofed ASAP:

It prevents structural damage

If you don’t put sealants on your bathroom walls and floor, water can seep through the cracks and trickle down into the subfloors. The moisture can reach plywood underneath and cause the wood to rot. It can also cause metal underneath the concrete to rust (concrete cancer).

Moreover, water can erode various materials and cause more cracks to form. Over time, this process can lead to extensive structural damage.

At first, it’s hard to notice if this is happening in your house. But once you start to see damp ceilings on the ground floor or water forming on lighting fixtures, these are usually signs that your bathroom is leaking heavily. 

If you want to avoid seeing severe structural damage and paying for costly repairs, you need to waterproof your bathroom as soon as possible.

It discourages mould growth

Without adequate waterproofing, your bathroom becomes a damp environment that spurs mould growth. Mould produces spores that can trigger nasal congestion, allergies, and respiratory infections. Moreover, water vapour from one’s bathroom can travel to nearby rooms, causing mould to spread all over the house.

It prevents paint discolouration

Water vapour that accumulates inside walls has a tendency to return to its liquid form through condensation. This process may lead to paint discolouration.

It offers enhanced insulation

Waterproof boards act as insulators that seal in warmth. If you don’t want to freeze inside your bathroom during winter, adding waterproof boarding is a great idea.

It increases the value of your house

Aside from looking at building design and aesthetics, buyers appreciate houses that have been thoroughly finished and will be less expensive to maintain. Waterproofing your bathroom makes your house more attractive if you put it on the market.

small bathroom waterproofing

Australian waterproofing standards

Bathroom waterproofing must comply with the Building Code of Australia and the Australian Standards (AS 3740-1994). Some of the requirements include:

  • Bathroom walls should be waterproofed to a height of 150mm above the whole floor substrate
  • Bathrooms on the second floor must have fully waterproofed walls
  • Areas above shower enclosures must be waterproofed to a height of 100mm
  • Shower enclosure walls must be waterproofed to 1.8 metres
  • Shower enclosure floors must be waterproofed
  • All internal and external corners and horizontal joints must be waterproofed in the shower area
  • Shower hobs must not be made of timber

Who should waterproof your bathroom?

Bathroom waterproofing is one of the jobs that you cannot DIY. Waterproofing a bathroom without a licence or proper training may affect future warranty and insurance claims on your house. Licenced waterproofers, tilers, and builders are usually equipped with the skill and materials necessary to complete the task.

In New South Wales and Queensland, professionals must have a waterproofer’s license. In other parts of Australia, waterproofers must provide a compliance certificate after the job has been completed. They should also cover the work with a warranty.

Before you hire a professional waterproofer, make sure to ask them if they are licenced and insured. They should also explain the extent of the warranty of their waterproofing materials.

Waterproofing materials

Professionals should have all the materials necessary for waterproofing. These include:

  • Waterproofing agent  
  • Waterproofing membrane
  • Silicone
  • Primer
  • Silicone gun
  • Paint scraper
  • Paint roller/brush

Steps to waterproofing a bathroom

Waterproofing should be done before tiling. Here is a quick step-by-step guide:

Step 1: Cleaning and priming

Clean the area to be waterproofed using a broom or a vacuum cleaner. Then, add primer on the walls and floors using a paint roller. 

Step 2: Seal all gaps

Look for any cracks where water might seep through. Usually, you’ll find them between the floor and the wall or near the shower. If they have been sealed before, remove the old silicone using a paint scraper. Then, reseal them using silicone. Wait for the seal to dry completely.

Step 3: Apply the waterproofing agent

Apply the waterproofing agent using a roller or a brush. You can start at the corner farthest from the door so you can access other parts of the floor or the wall easily.

applying bathroom waterproofing

Step 4: Install the waterproofing membrane

Cut the waterproofing membrane to the size appropriate for the bathroom. Then, lay it down on the floor or the wall. Paint over it using the waterproof agent.

bathroom waterproofing membrane

Step 5: Apply the waterproofing agent to other sections

Once the membrane is dry, coat the entire floor and the wall with the waterproofing agent. Then, wait for the coat to dry completely.

bathroom waterproofing for wall

Step 6: Add a second coat

After the first coat is dry, paint a second coat in opposite strokes. Wait for the second coat to dry completely before starting any other construction work in the bathroom.

How much does bathroom waterproofing cost?

Generally, bathroom waterproofing costs $500 to $750*. The cost may be higher for more spacious or second-storey bathrooms. Usually, most professionals factor in bathroom waterproofing together with the total cost of bathroom renovation.

To get a clear idea of how much your bathroom renovation project will cost, request a free quote. We can also help you find reliable builders who can carry out the work on your home.

*Rates are rough estimates only.

Tips for waterproofing your bathroom

Installing a waterproofing membrane to the floor and the walls of your bathroom is only one step to making sure it’s free of excess moisture. To keep water away from sensitive parts of your home, try the following tips:

Pick waterproof materials

Making your bathroom 100% waterproof starts with building design. Make sure to pick materials that are impervious to water, especially for the following:

  • Floor and wall tiles: Use stone, metal, plastic, ceramic, or porcelain tiles since these materials are resistant to moisture. They’re also more resistant to mould and mildew compared to organic materials. If you’re concerned about appearance, you can look for ceramic or porcelain tiles that mimic wood planks.
  • Benchtops: Use solid, nonporous materials for benchtops, such as quartz. Be careful not to use benchtop materials with Medium Density Fiberboard (MDF) cores, which may rot when wet.
  • Non-tiled walls: Use special wallboards with waterproof facing. Standard wallboards have paper facing, which is susceptible to water damage.

Add an exhaust fan

Every bathroom needs an efficient exhaust fan to expel moisture. If you have extra room in your budget, try to buy exhaust fans with heat bulbs, which help in dispelling moisture from a bathroom.

new bathroom with vent

Check your baseboards

It’s better to use PVC baseboards instead of plywood or solid wood baseboards for your bathrooms. Make sure that there are no gaps at the top (which is connected to the wall) or the bottom (which is connected to the floor).

Seal cracks and holes

Water always finds cracks and holes in the bathroom floor and walls. That’s why you should always make sure that all cracks are properly caulked using bathroom-grade silicone. 

Pay special attention to the corners where benchtops meet the walls and between the walls and floors. Another area that should be sealed and watertight is the area around fixtures like bathtubs and showers. Inspect these annually to ensure that there are no cracks.

Frequently asked questions

How long does it take to waterproof a bathroom?

Generally, it takes 2 to 5 days to waterproof a bathroom, depending on the climate. Also, you need to allow the waterproofing agent to fully cure before you install tiles or do other types of work in the bathroom.

Why do homeowners skip bathroom waterproofing?

Some homeowners skip or delay waterproofing to save on costs. Aside from that, waterproofing takes several days to finish and may delay the renovation timeline.

How do you test bathroom waterproofing?

Homeowners should do flood testing to see if the waterproofing membrane prevents water from seeping through cracks and leaking into the ceiling.

You can do this by plugging your floor drain and filling the bathroom with water. If the water retains the same level for 1-3 days, then that means that your bathroom was successfully waterproofed.

Is bathroom waterproofing toxic?

It depends on the products that you use, though there are waterproofing solutions that are toxic and emit unpleasant odours. The smell lasts anywhere between 4 to 5 days. During this time, you may opt to light scented candles or use a fan to blow out chemicals in the air.

bathroom waterproofing mortar

What are the causes of faulty bathroom waterproofing?

There are a few reasons waterproofing can fail, such as:

  • Inadequate preparation: Before applying any waterproofing products, make sure to clean and prime all surfaces thoroughly.
  • Incorrect application: The waterproofing membrane must cover the entire wet area.
  • Substandard waterproofing product: Low-quality waterproofing membranes can leak and fail.

How long will bathroom waterproofing last?

High-quality waterproofing membranes usually come with a 7-year warranty*, though they usually last longer. If you start to notice peeling paint, mouldy ceilings, and walls stained with water, your bathroom may have already started leaking. This means you will need to peel off all your bathroom tiles and reinstall a new waterproofing membrane on the floors and walls of your bathroom.

*The warranty varies depending on the manufacturer. Ask your waterproofer for more information.

Hire a professional waterproofer now

When updating your bathroom, don’t forget bathroom waterproofing. It’s essential in preventing excess moisture from accumulating in your home. Without it, your house is at risk of developing extensive structural damage. Bathroom waterproofing also prevents mould and mildew from spreading. 

At Superdraft, we have building design and drafting professionals who can help you design an aesthetically pleasing and watertight bathroom. We can also connect you to reliable builders who can ensure that your project is executed smoothly. Sign up for our free platform today!

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