How to waterproof a bathroom

Bathrooms, unlike ordinary bedrooms, are prone to getting damp. The moisture and steam from a bath or shower will condense on the walls and drip down to the floor. If the underlying concrete floor and walls are not covered with a waterproof coating, they can be damaged by the moisture and mould could begin to grow. A waterproof coating will prevent moisture seepage in the walls and the floor.

Contractors need to take special care when building bathrooms and toilets, especially when it comes to the plumbing. They need to be precise when laying pipes and hoses in the walls and floors of the bathroom or toilet – any loose joints in the plumbing can result in internal leaks and costly repair work to the concrete structure.

There are basically two types of waterproof coating, or membranes, that contractors can use to protect the concrete from moisture damage. They are sheet membrane and liquid membrane. These membranes are applied to the floor and walls; a double layer is applied along all the corners of the room to provide extra protection in these vulnerable areas.

Tools needed to waterproof a bathroom

  • Brush
  • Scraper
  • Paintbrush
  • Roller tray
  • Caulking gun
  • Primer
  • Silicone
  • Masking tape
  • Waterproofing membrane

Steps to make a bathroom waterproof

  1. The concrete surface needs to be clean and free of dust, contaminants and loose particles. Use the brush to clean the walls and then use the scraper to remove loose debris from the floor.
  2. Use the roller brush to apply primer to the concrete floor and walls of the bathroom, shower or toilet.
  3. Once the primer dries, apply a layer of level masking tape at the required height along the walls. This will ensure that the waterproofing is completed to a uniform height along the walls. In showers, the whole wall will need to be waterproofed, but in toilets, only the bottom 30cm of the wall needs to be coated.
  4. Apply silicone to all the vertical and horizontal corners of the room. Scrape the silicone smooth with a finger to ensure a tight and clean seal along the corners.
  5. Apply the first coat of waterproof membrane. A liquid waterproof membrane is essentially a paint that can be applied with a brush. Sheet membranes need to be attached with tape and then painted over with an adhesive. Start at the corners and apply the waterproof coating, making sure that there is complete coverage, especially along all the corners and plumbing joints.
  6. Once the first coat has dried, apply the second coating. Carefully brush the corners and joints to ensure a tight seal and no gaps for moisture to seep into. Leave to dry again and remove the masking tape.

Some contractors like to use a mixture of liquid and sheet membranes. The sheet membrane is applied along all the corners of the room, then a liquid coating is painted over the top of the sheet and across all the flat surfaces of the bathroom. This ensures complete protection against the effect of moisture on concrete, as well as preventing the growth of mould internally.


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