Is it necessary to waterproof under tile installations?


Chesapeake homes is building our new home in Norfolk Virginia, our first meeting last Friday with the site superintendent reveal my worst nightmare! They don’t do waterproofing under the tiles!! He claimed, it’s never been done on any of their construction, he also swear all is needed is an annual grout sealing which is the homeowner responsibility. HELP! I’ve spent many days learning about proper tiling online And am convinced that waterproofing is a must! Builder is scheduled drywall install as of yesterday 3 Aug. Thank you!


ANSWER - It depends on the application on whether waterproofing under a tile installation is necessary.  If it is in a wet application and in some exterior applications, then it is necessary to waterproof the tile assembly.

Interior tile showers require waterproofing for both the shower floor and walls.  The plumbing code requires waterproofing the floor with either a waterproof sheet membrane or hot mop waterproofing or a liquid applied waterproof membrane.  The waterproofing has to be over a sloped surface at 1/4" per foot and the drain weep holes have to be protected.

The tile shower walls need to either have a moisture barrier building paper between the studs and the mortar bed or cementitious backer board.  Some backer boards are waterproof themselves like foam backer boards or the Glass Matt or Fiber Resistant Gypsum backer board that you don't put building paper behind it, but you do need to seal all of the joints and transitions of the backer board.

Often today a secondary waterproof membrane can be applied to the surface of the floor mortar bed or the wall mortar bed or backer board to keep the moisture out of the cementitious materials and limit the exposure.  This can avoid efflorescence staining and musky odors and other potential issues. The tile is then adhered to the membrane.

Any exterior deck application above grade needs to be waterproofed.

4 thoughts on “Is it necessary to waterproof under tile installations?

  1. Jess aquino says:

    Yes it is the shower wall tile on the second floor that I’m talking about, How can I convince the builder to waterproof The shower stall/ walls. The standing shower will also have a seat . Both showers have an acrylic pan and a glazed tub. This is our first brand new home. Thanks again, your advice will be a tremendous help!

    • Donato Pompo says:

      If the tile walls have a moisture membrane behind the substrate or if the substrate is made of waterproof material then you don’t have to waterproof it.

      Make sure that the shower wall substrates are not gypsum green board that is not waterproof. Any horizontal substrate surface has to be fully waterproof under the tile, so if it is a tile seat over a structure and not free-standing it needs to be waterproofed.

  2. Jess Aquino says:

    SC tynes contractor installed shower tile using APAC 750 cover adhesive, it s seeping through grout everywhere, it s also not waterproof and cement board gaps were not taped up. It has been two years, is this means that moisture is now present behind the substrate? These were done on two standing showers and one over a tub. What can be done? Thank you!

    • Donato Pompo says:

      Apac 750 is a rubber and vinyl cove base adhesive. It should not have been used to install ceramic tile and not in a shower. Not sure why it would bleed through the grout joints. Not sure whether a waterproof membrane was installed or a moisture barrier behind the backer board.

      The only way to get rid of the wrong adhesive is to replace the tile and then install it correctly.

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