Waterproofing is an essential part of any domestic bathroom construction or renovation. In fact, bathrooms without adequate waterproofing can cause a range of serious problems including rising damp, corrosion of plumbing, compromised electrics, mould, mildew, warping and rotting of a timber floor and structures, and concrete cancer.
Unfortunately, not everyone is getting the message. As the Australian Master Tilers Association points out, inadequate bathroom waterproofing is one of the top three domestic building defects found in Australia and can cause as much structural damage to a house as termites.
Australian waterproofing bathroom standards
The minimum requirements for waterproofing bathroom are set out by the Building Code of Australia and the Australian Standards (AS 3740-2010), which states that:
- The full floor within the shower room must be waterproofed.
- The hob or step down onto the bathroom floor must be waterproofed by at least 100mm
- The entire floor where the bathroom is located must be waterproofed (second story and higher).
- The walls inside the shower must be waterproofed by at least 150mm.
- The vertical angle between any two walls in the shower must be waterproofed by at least 1800mm high.
What materials and tools are required to waterproof a bathroom?
Bathroom waterproofing should be carried out with quality products (waterproofing agent and waterproof membrane). On top of that, you require silicone and primer.
In terms of tools, you require a silicone gun, masking tape, a paint scraper, a paint roller or paint brush, a paint tray, a spirit level, a utility or stanley knife, a broom, a dustpan, and a vacuum cleaner.
Is waterproofing a bathroom a DIY job?
When you consider the regulations stated above as well as the list of things that a poorly completed job can lead to, the short answer to this question is no. On top of that, anybody who tries to do it as a DIY job should realise that it can also affect warranty and insurance claims.
In any case, DIY jobs are not actually allowed in NSW and Queensland. In those two states, the task must only be carried out by a licensed professional. In the other states, while licensing is not required, all work must meet the Australian standards, as set out above. So, DIY is off limits to everybody but skilled tradespeople who really know how to waterproof a bathroom.
How much does waterproofing a bathroom cost?
Across Australia, costs to waterproof a bathroom vary by location. For example, at the lower end of the scale the job costs about $30 - $45/m², while at the other extreme in Adelaide it costs around $40 - $55/m². In other words, on average it costs around $500 to waterproof a small bathroom in Australia.
How to waterproof a bathroom - a step-by-step guide
Step 1 - Clean the bathroom floor
Use whatever you need (vacuum cleaner, dustpan & broom, etc.) to ensure your wet area is spotless and ready to work on.
Step 2 - Apply the primer
The primer should be applied to the floor and also to the walls up to a height of 20-30cm, with a normal paint roller or brush. It’s best to start on the walls at the back corner and work your way around, and then complete the floor.
Step 3 - Fill in the gaps with silicone
After the primer is dry, the next step is to fill any gaps (between floor and wall, around the vanity, near the shower, at the shower base, etc.) with silicone. First remove any old silicone with a paint scraper, Stanley knife, or something similar, then apply the new silicone. Wait approximately 24 hours for it to dry, sealing any potential gaps.
Step 4 - Use masking tape around walls
To ensure your bathroom waterproofing is completed with a straight edge, apply masking tape as you would when painting.
Step 5 - Apply the waterproofing agent to the walls and corners
Again, this can be applied with a roller or brush. Starting at the back corner for ease of access, apply around the wall up to the height of your masking tape and then where the wall and floor meet.
Step 6 - Add the waterproof membrane
A waterproof membrane should then be added to the wall and the cracks in the floor. First cut the product into appropriate lengths and place it into position. Then paint over it with the waterproofing agent to stick it down. Ensure you paint over it completely and leave no gaps.
Step 7 - Apply the waterproofing agent to the rest of the floor
Wait for the membrane, which is now covered in the waterproofing agent to dry. Then, the next step is to cover the entire floor in waterproofing agent. This is just the first coat. Do you need to do another coat? Yes.
Step 8 - Apply a second coat
The first coat will take about 24 hours to dry. Once this has been done, you are ready to apply a second coat, which should be applied in a different direction to the first (i.e. diagonally). This will take at least one more day to dry.
Then, it is important to allow the waterproofing to fully cure before tiling or doing any more work in the bathroom. Depending on the climate, this can take up to five days.