How to waterproof tile

Written by larry simmons
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How to waterproof tile
Worker grouting tiles prior to applying a waterproofing sealant. (tile layer image by Greg Pickens from

Installing tiles in any moisture-laden environment, whether it's outdoors where they are exposed to the elements or in a bathroom or kitchen, requires that you make an effort to waterproof them. Water can be destructive to tiled surfaces, seeping beneath the tiles and damaging the subsurface, interfering with the binding adhesive and staining the tiles themselves. Preventing the damage that comes with moisture takes careful panning throughout the installation process, from preparing the subsurface to finishing the tiles after placement. Done correctly, you'll see no water damage and be able to enjoy your tiled surface for decades to come.

Skill level:

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Things you need

  • Silicone caulk
  • Fibreglass tape
  • Thinset mortar
  • Trowel
  • Plastic vapour barrier
  • Asphalt mastic
  • Notched trowel
  • Spray adhesive
  • Utility knife
  • Tiles
  • Tile adhesive
  • Grout
  • Grout float
  • Sponge
  • Water
  • Lint-free cloth
  • Tile and grout sealant

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  1. 1

    Cover any seams in the surface that you're tiling to prevent water from seeping through to the tiles. If installing backer board as a tiling surface, leave a joint between each piece between 3/16 and ¼ inch wide. Fill the joints with silicone caulk to keep water from seeping through. Level the caulk with the surrounding surfaces using a wet fingertip to mould the caulk in place. Tape fibreglass tape across joints between tightly butted tiling surface boards if a gap isn't present. Cover the fibreglass tape with a thin layer of thinset mortar. Spread the mortar over the tape with the flat of a trowel, scraping the mortar with the edge of a trowel. Allow the thinset to set for an hour.

  2. 2

    Cover the surface that you're tiling with a vapour barrier. Spread a thin layer of asphalt mastic over the tiling surface using the flat side of a notched trowel. Tilt the trowel 45 degrees and then go over the mastic with the notched edge to raise ridges. Wait 30 minutes for the mastic to set and then spread the plastic vapour barrier evenly over the mastic. Press the barrier down firmly to stick. Overlap the sides of adjacent barrier pieces four inches. Secure the overlapped portions of plastic barrier by spraying the rear of the overlapping flap with spray adhesive and then pressing the flap to the plastic barrier sheet beneath. Use a utility knife to cut the plastic barrier when needed around electrical sockets or ducts, sealing the plastic edges to the edges of the outlets or ducts using a spray adhesive.

  3. 3

    Install the tile to your tiling surface. Spread a layer of your chosen tile adhesive onto the surface and then mount the tile according to your design needs. Leave a space between the tiles and the surface of any bathtubs or sinks of ¼ to 3/8 of an inch to prevent water from running up to the tiles from the wet surface.

  4. 4

    Grout the joints between the tiles using a grout float to push the grout into place. Wipe the surface of the tiles with a damp sponge within 15 minutes of grouting to remove any excess material. Wait 2 hours and then go over the surface of the tiles with a dry lint-free cloth to remove any grout residue from the surface.

  5. 5

    Fill the joint between the tiles and the bathtub or sink with silicone caulking. Mold the surface of the caulking flat with a wet finger.

  6. 6

    Allow the grout to cure for a week before sealing the tile and grout.

  7. 7

    Seal the surface of the tiles and grout using a tile and grout sealant. Brush the sealant onto the face of the tiles and over the joint lines, covering the surface completely. The sealant provides a protective waterproof layer that also prevents staining. Allow the sealant to dry for 48 hours before using the tiled surface.

Tips and warnings

  • Seal unglazed stone tiles prior to grouting to prevent the grout from discolouring the tile surface.

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