How much does it cost to waterproof a bathroom?

How much does it cost to waterproof a bathroom feature image

How much does it cost to waterproof a bathroom and how can you get the job done just right?

Waterproofing is one of the most crucial stages of any bathroom renovation project. If the job isn’t done right, water can leak into the floor and walls and cause major structural damage to your home.

So what does waterproofing a bathroom involve and how much does it cost? Read on to find out.

What is waterproofing and why do I need to waterproof my bathroom?

The bathroom is the largest wet area in your home. Waterproofing involves applying a special membrane, paint, spray or sheeting product to ensure that no water escapes from that wet area into other areas of your home.

If your bathroom isn’t properly waterproofed, water leaks can cause significant damage to your property. Mould, mildew, rising damp and peeling paint can all result, but there can also be much more severe consequences including rotting and warping of structural timbers or corrosion of metal.

How much does it cost to waterproof a bathroom?

Costs vary depending on the contractor you choose to carry out the work and the waterproofing materials they use. However, as a general guide, waterproofing a bathroom costs anywhere between $35 and $60 per square metre.

For an average-sized bathroom, expect to pay somewhere in the vicinity of $500 to $800, although costs will vary for smaller and larger spaces.

If you’re purchasing materials for a waterproofing project, you’ll need a few products. These include:

  • Primer. This enhances the adhesion between bathroom surfaces and waterproofing products. One litre of Dunlop Primer & Additive will set you back $16.90 at Bunnings.
  • Waterproofing product. This is the membrane you apply to stop water leaking out of your bathroom, and spray or paint-on products are the most popular options in Australia. To give you an idea of costs involved, 20kg of Dunlop Express Wet Area Waterproofing, a water-based acrylic polyurethane waterproof membrane, costs $210. Four litres of Dunlop Undertile Waterproofing, a membrane designed to be used under tiles which can be applied with a brush or roller, is $89.
  • Bond breaker. Used to stop the waterproofing membrane adhering at bathroom joins, bond breaker is an essential item for your shopping trolley. Crommelin 200mm x 50mm Reinforcing Fabric from Bunnings costs $85.

The rules and regulations

Before we get to the finer points of bathroom waterproofing, it’s important to start with the fact that your bathroom waterproofing will need to comply with specific regulations outlined by the Building Code of Australia and Australian Standards (AS 3740-1994). They stipulate that in residential bathrooms:

  • The full floor in the shower recess must be waterproofed, and shower walls should be waterproofed up to a height of 1,800mm
  • Bathroom walls need to be waterproofed up to a height of 150mm
  • If your bathroom is on the second floor or higher, or if the flooring contains wood, the whole floor must be waterproofed
  • The area over the step down to the floor from the shower must be waterproofed to at least 100mm

Of course, these are just the minimum requirements, so it’s best to go above and beyond what’s listed here to reduce the risk of home damage due to insufficient waterproofing. For example, even if your bathroom is on the ground floor or doesn’t contain any timber, it’s a good idea to waterproof the entire floor. You may also want to waterproof the areas around the bath, vanity and toilet.

In some areas, the local council will also need to inspect the waterproofing work completed by a licensed waterproofing professional, so make sure you’re aware of whether this requirement applies where you live.

Who can carry out waterproofing work?

In NSW and Queensland, only someone who has a waterproofer’s licence can carry out waterproofing work. Most qualified waterproofers will have completed a Certificate III in Construction Waterproofing. There are specialist waterproofers available, but some people working in related trades, such as tilers, may also have the necessary qualifications.

In other states and territories a licence isn’t required, but whoever does the work needs to provide a statement declaring that the work complies with Australian Standard AS 3740 – Waterproofing of domestic wet areas.

Most hardware stores sell waterproofing products, and attention to detail is crucial. Not only do you need to follow the instructions exactly, but you also want to be absolutely meticulous so you don’t miss any spots.

If you DIY, be aware that your work will need to pass a once-over from a building inspector and could also have potential consequences for any insurance claims you may have in the future.

How to waterproof a bathroom

Bathroom waterproofing is done before tiling occurs. Before any waterproofing membrane can be applied, the areas to be treated will first need to be correctly prepared and primed. Special attention needs to be paid to wall and floor joins, with all surfaces left smooth to guarantee unbroken coverage by the waterproofing membrane.

Once the primer has been applied, silicon sealants are used to waterproof areas where bathroom features, for example the vanity unit, meet the walls. This will ensure that no water gets in behind these features, where it could potentially cause damage.

Special attention also needs to be paid to edges and corners, which are other danger areas for water leaks. A neutral cure silicon is used to seal these areas, while a polyfab (polyester fabric) bandage is also used over these joins to create a “bond breaker”.

This flexible bond breaker stops the waterproofing membrane from adhering at joins – without it, small shifts in the building over time could wear away the membrane. A bond breaker is also required around taps, drains and other fittings that break through the membrane.

A liquid rubber waterproofing membrane can then be applied to the relevant bathroom surfaces. The first coat is done horizontally and, once it has dried, the second can be applied vertically to cover any small gaps that may have been missed the first time.

Once the waterproofing has been applied, you’ll need to give it enough time to dry and cure, so depending on the climate where you live you might have to wait up to five days for this to occur. Many waterproofing products come with a 10-year warranty, but if the job is done right by a licensed professional, expect it to last much longer.

How to hire a bathroom waterproofer

Before you choose a licensed waterproofer to work on your bathroom renovation, make sure you’ve found the right person for the job. Ask them the following questions:

  • Are you licensed to carry out waterproofing work?
  • Do you have insurance cover?
  • How much experience do you have? Do you have references I can contact?
  • How long will my bathroom take to waterproof?
  • How much will it cost?
  • What warranty applies to your work and the waterproofing product you use?

Make sure you compare a number of quotes before deciding on the right contractor to complete the work.

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