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How to waterproof your bathroom

Last Updated Mar 28, 2017 · Written by Richard Kempthorne

Bathrooms are the major wet area in the house and it is important that the bathroom is correctly waterproofed in order to reduce the risk of structural damage occurring as a result of dampness, water leaks, or condensation.


Requirements for waterproofing a bathroom

The process of waterproofing

Tools need to waterproof a bathroom

Step by step guide on how to waterproof your bathroom

Requirements for Waterproofing Bathrooms

The Building Code of Australia and the Australia Standard (AS 3740-1994) outline the minimum requirements for the waterproofing in residential bathrooms.  These requirements include:

  1. waterproofing the full floor within the shower recess
  2. at least 100mm over the hob or step down onto the bathroom floor should be waterproofed
  3. at least 150mm up the walls inside the shower walls needs to be waterproofed
  4. the vertical angle between any two walls in the shower needs to be waterproofed up to at least 1800mm high
  5. the entire bathroom floor needs to be waterproofed if it's timber flooring, plywood or particleboard, or if it is above the ground floor of the house

applying water proofing product to a bathroom floor


However, to provide the best insurance against water damage, it is a good idea to go beyond these minimum requirements and ensure that all of the walls within the shower recess are waterproofed as well as the entire bathroom floor. To get a visual on this, see these photos of bathrooms by trade professionals.

Be aware also that some councils will require that waterproofing be done by licensed waterproofing applicators so you should check with your local council before any waterproofing work is undertaken.

The Process of Waterproofing

It is vitally important that when you undertake a bathroom renovation all the surfaces within the bathroom are correctly prepared and primed.  Especially of importance are any joins between the wall and floor, between the walls themselves, and around any drains in the floor.  Ensure that the surfaces are smooth and free of any loose particles, which may affect the integrity of the waterproofing membrane.  A polyester reinforcement mat should be fitted into all the internal corners of the shower recess, such as the junctions between the wall and floor, the hob and the floor, and the corner formed by two walls meeting.  The waterproofing membrane will then be applied to all surfaces.  Once the first coat has been applied, an hour or two will be required before the second coat can be applied.  The second coat should be applied in a different direction to the first – for example, if the first coat was put on vertically, the second should be horizontal.  Do not use the bathroom until the waterproofing has had a chance to fully cure – this can be as long as five days, depending on your climate.

A tradesman applies silicone to gaps in a bathroom to waterproof it

Tools needed to waterproof a bathroom

 Silicone and Silicone Gun

Use a silicone gun tio water proof your bathroom

Masking tape

Masking tape to help with bathroom waterproofing

Paint scraper

A paint scraper helps with prep for bathroom waterproofing


Paint roller and tray

Paint tray and roller

Paint mixer

paint mixer for waterproofing

Spirit level

A spirit level to help with waterproofing your bathroom

Utility knife

A utility knife is useful for your waterproofing project

Dust pan & brush, broom or vacuum cleaner

dust pan and brush

How to waterproof your bathroom step by step guide

How to Waterproof a bathroom step 1

Use a broom. dust pan and brush or a vacuum cleaner to thoroughly clean the floor of any dust and dirt.

How to Waterproof a bathroom step 2

The next step to waterproofing your bathroom involves applying the primer.

Transfer the primer to a painters roller tray and use a decent roller to apply it.

Start applying the primer from the back of the room.  Roll it evenly around the bottom half of the wall.  Once you have applied primer to approx. 30 cm of the bottom of the  wall you can continue to use the roller to cover the bathroom floor.

How to waterproof a bathroom step 3

Once the primer has completely dried you can start thinking about sealing up all of the gaps with silicone.

Firstly remove any old silicone from the areas you are going to seal up.  You can use a paint scraper or a stanley knife or blade.  

Take a look at the gaps and then judge what size nozzle you will need to sufficiently fill the gaps with silicone, try placing the nozzle directly onto the space you will be filling.

Once you have determined the size use a stanley knife or a pair of scissors to cut a hole in the tip of the nozzle sufficient enough to create the seal.

Hold the silicone gun at a 45 degree angle.  Then squeeze the trigger whilst simultaneously moving the gun along the line you are sealing up.  It can sometimes help to lick your finger and run it along the silicone you have just applied to smooth it over and tidy it up.

Now let the silicone dry for 24 hours.

How to waterproof a bathroom step 4

To help you cut in like a normal painting job you can stick masking tape around the wall.  Place masking tape up to the height you want to waterproof this will help give you a straight edge and will prevent paint from splashing onto areas you don’t want it to.

How to waterproof a bathroom step 5

Applying a waterproofing product is the next stage to completing your bathroom waterproofing project.

To make life easier start applying the waterproofing product in the far back corner of the room.  Again you can use a roller to apply the product. Run the roller around the wall width ways from the where the floor meets the wall up to the height of the masking tape you stuck to the wall.

How to waterproof a bathroom step 6

The next stage is to add the waterproof membrane.  Find yourself a good quality product.

Take the waterproof membrane sheet and cut lengths to fit the wall and cracks on the floor.

You can use a paint roller or paint brush to stick the membrane down using the waterproofing product.  Keep doing this until there are no gaps and fully painted over.

How to waterproof a bathroom step 7

Once the membrane has been painted over with waterproofing product and dried you can start painting the entire floor.  It typically takes around 24 hours to be completely dry.


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