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How To Waterproof a Bathroom

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Things you'll need

  • Paint brush (4 inch)
  • Paint Roller
  • Gloves
  • Hacksaw
  • Flexible Sealant and Silicon Gun
  • Aluminium Angles - L shaped. Length is determined by your door opening width plus the length of each side of the shower base (if hob-less) and distance from floor waste to door.
  • Primer Agent (1 coat)
  • Waterproofing Agent (2 coats)

Consult your supplier on personal protective equipment.


Clean area to be waterproofed. Vacuuming is recommended.

Be sure the walls are completely clean and dry.

Inspect the walls and check for any dabs or nails protruding from the wall and remove them.

Place bond breaker around floor and wall junction, any hob and floor junction as well. Cut to length and fix down with sealant.

Applying the Primer Agent

Open the window, for ventilation. Place your mask on.

Apply primer agent to the area you need to waterproof. This helps the waterproofing membrane bond to the floors and walls.

Wait for the primer to dry (refer to instructions on the tin)

Once dry, apply sealant to all the internal joints eg, shower hob, internal shower corner, and floor to wall junctions. Fill all gaps and cracks and seal around floor waste.

Cut a piece of aluminium angle using a hacksaw to the size of the door opening. Be sure to measure from the inside door opening.

Place some sealant on the bottom of the angle with the bottom flange pointing to the inside of the bathroom. Place across door opening, and press firmly.

If your shower is hob-less, be sure to place the aluminium angle to the perimeter of shower base, right where your shower screen is going, in the same way you did the angle for the door opening.

Allow sealant to dry.

Once dry, it is time to apply the waterproofing membrane.

Ensure the right type of waterproofing membrane is being used and read the manufacturer's instructions carefully, following each step as suggested.

Applying the Waterproofing Membrane

Now it's just like painting.

Use the Paint brush to apply the waterproofing membrane to the corners, upturns, floor waste and junction to floor.

You may now use the paint roller to do the walls.

Once the walls have been done, start the floor, working your way out of the bathroom.

Once dry, apply a Second coat as per above.

As soon as the second coat dries, you are done!

More Information

More information can be found at the BSA website.

Return to Bathroom

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