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    How to waterproof a bathroom

    To Australian standards

    Hannah | Oneflare

    If you’re undertaking a bathroom renovation, it’s absolutely essential you know how to waterproof a bathroom correctly.  While it isn’t the most glamourous part of building your new bathroom, an incorrectly or inadequately waterproofed bathroom can cause serious damage to the structure of your home and can be extremely costly to fix.

    Waterproofing is needed to protect the concrete base of the bathroom from the adverse effects of dampness. The waterproofing layer is a guarantee of the safety of walls, ceiling and floor in case of emergency situations associated with leaks, flooding and pipe breakthroughs.

    All bathrooms require waterproofing / Source: Start2Finish Interiors Design Management

    Increased humidity, temperature changes, the periodic formation of steam and condensate – all of this has an adverse effect on the finish, the decor of the bathroom, on the floor. Moisture penetrates through the seams under the tile, accumulates under the tile, in places of laying and joints of pipes and communications, creating comfortable conditions for the appearance and reproduction of mould, fungi and harmful bacteria.

    While there are parts of a bathroom renovation you can DIY, it is imperative that waterproofing is undertaken by a licensed professional. In short, it is simply too important that waterproofing is done correctly – even a tiny gap may cause serious damage to the internal structures of your home causing heartache and costing money down the track.

    In Victoria, the work must be done by a qualified and licensed waterproofing tradesperson who can provide a written guarantee of workmanship and a warranty.

    What are Australia’s waterproofing standards

    Waterproofing must comply with regulations as set out by the Building Code of Australia and Australian Standards (AS 3740-1994).

    To briefly summarise the requirements of the standard are:

    Shower floorShower waterproofing is essential and the entire shower floor must be waterproofed
    Shower wallsShower walls should be waterproofed up to 1800mm high
    Bathroom floorIf the bathroom floor is made of wood or contains wood OR if the bathroom is on the second story or higher, the entire floor must be waterproofed
    Bathroom wallsBathroom walls must be waterproofed up to 150mm high
    Step downOver the hob or step down onto the bathroom floor should be waterproofed to 100mm high

    These are the minimum requirements, however depending on how the bathroom is intended to be used, the areas around the bath, toilet and vanity may also need to be waterproofed.

    Tools needed for this job:

    • Cleaning equipment (Dust pan and brush / broom / vacuum cleaner)
    • Safety equipment
    • Caulking gun
    • Paint roller and tray
    • Rubber hammer
    • Silicone gun
    • Masking tape
    • Paint scraper
    • Paint mixer
    • Spirit level
    • Utility knife


    • Primer
    • Silicone
    • Waterproofing agent
    • Waterproofing membrane

    How a bathroom floor is waterproofed

    This is a step-by-step guide to how a bathroom is professionally waterproofed, it is written for waterproofing preparation rather than a DIY guide.

    Step 1 – Prepare the area

    After the old bathroom has been removed, the area must be completely clean and free of dust and other particles before waterproofing can start.  The area is cleaned using a broom and a dustpan and dried in all wet areas.

    Both the walls and the floors should be perfectly smooth. If the floor is uneven, you can use a levelling compound to smooth it.

    Tip! To obtain perfectly smooth vertical surfaces, the walls treated with waterproofing can be sheathed with moisture-resistant gypsum plasterboard.

    Step 2 – Apply the primer

    Using a paint roller and roller tray, the primer is applied starting from the back corner of the bathroom.  The primer is applied to 150mm up the bathroom walls and the entire bathroom floor is covered.  Primer is allowed to dry.

    Step 3 – Fill the cracks with silicone

    Using the silicone gun, the silicone is applied to the gaps between the wall and floor and any other gaps or cracks.  Silicone is allowed to dry over 24 hours.

    Step 4 – Apply masking tape

    Masking tape is used to mark the level to which the waterproofing agent must be applied according to the Australian Standards.

    Source: Esteem Building & Renovations

    Step 5 – Apply waterproofing agent

    The waterproofing agent is painted on to the height of the masking tape starting from the back corner. The waterproofing product must be applied with a trowel in 1mm thickness.

    The seal obtained by a coating reliably prevents the ingress of moisture and destruction, while the material cost is much lower than with the use of liquid compounds and plates, and the work can be performed qualitatively with one’s own hands.

    Important: The room in which the work goes, you need to constantly ventilate. To avoid poisoning by vapours of the mixture, it is desirable to use a protective mask.

    Step 6 – Apply waterproofing membrane

    Roll out the membrane and cut to the lengths of the floor.  The membrane is applied, making sure that it covers the cracks and the joints in the floor.  The entire area is covered with membrane and painted over with waterproofing agent to make sure it sticks down.  When the entire area is covered with membrane and waterproofing agent, it is left to dry for 24 hours.

    Step 7 – Apply second coat of waterproofing agent

    A second coat of waterproofing to the entire area and left to dry for 24 hours.

    The area is now waterproofed and ready for your new bathroom to be installed.

    How to waterproof timber floors in the bathroom

    Waterproofing timber floors in the bathroom is crucial to ensure they remain in good condition. Bathrooms are high-traffic areas, subjected to moisture, and susceptible to wood rot and damage. Waterproofing the timber floor adds an extra layer of protection against water, dampness, and mould that can cause havoc in your bathroom. Here are some benefits of waterproofing timber floors in the bathroom.

    Benefits of Waterproofing Timber Floor in the Bathroom:

    1. Increases Durability: A waterproofed timber floor will last longer since it’s made water-resistant and less susceptible to moisture damage and rot. This means you will save money on repairs and replacements over time.
    2. Enhances Safety: Damp, mouldy, and slippery floors pose a considerable risk, especially in a bathroom where water is frequently used. Waterproofing your timber floor reduces the health hazards and potential injuries caused by slipping.
    3. Easy Maintenance: Waterproof treated timber floors are easy to clean, and you do not have to worry about water damage, mould, and mildew buildup. Regular cleaning with a mild detergent is enough to keep the floor clean.
    4. Improves Aesthetics: A waterproofed timber floor adds an extra layer of aesthetic value to your bathroom. You can choose different waterproofing finishes that enhance the look of the timber floor, such as clear finishes that bring out the natural timber allure or a tinted finish that matches the bathroom’s interior colour schemes.

    Methods of Waterproofing Timber Floor in the Bathroom:

    Sealers: Sealers create a barrier over timber that fills gaps and cracks, repels water, and increases the timber’s lifespan. Look for sealers designed explicitly for bathroom floors and ensure it’s compatible with your timber floor type.

    1. Membrane Systems: Membrane systems are more effective in preventing water damage since they cover the whole floor area and provide an unbroken barrier. This layer is then covered with tiles or vinyl flooring, making it a permanent solution.
    2. When considering waterproofing your timber floor in the bathroom, there are various factors to consider, including the type of timber, bathroom’s traffic flow, and the extent of damage. Hire a professional for expert advice and to ensure that the waterproofing process is done correctly.

    In conclusion, waterproofing your timber floor in the bathroom is a smart investment. It will keep your bathroom floor looking great and prevent water damage to the subfloor and the expansion of mould and mildew. As with any home project, seek advice if in doubt, and always ensure safety measures are put in place.

    DIY vs Contractors

    We strongly recommend that a qualified and licensed professional is hired to do the work.  Even if in certain areas the laws allow you to do it yourself, the consequences of incorrect waterproofing can be very expensive, and not worth the risk.

    Waterproofing when done correctly will penetrate beneath the surface and actually treat the masonry.  This precaution will save you much heartache should there ever be a burst pipe, flooding or any other event that could cause water damage to your home, investing in an expert to waterproof your bathroom is a must.

    A professional waterproofer will guarantee the work for up to 15 years, often much longer than that, and the job when done professionally can last 25 years or more.  Make sure you ask to see their license and insurance associated with the work before you sign them up for the job.

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