Is it necessary to waterproof under tile installations?

QUESTION

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

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.

8 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.

      • Aryana Farsai says:

        Thank you in advance for your knowledable answer, I hope to hear from you so as I am working to finish a 6’x6′ newly poured 8-10″ think concrete slab – I have designed no covering shade, receiving 1/2 direct day sun so I would like the best quality – and longest lasting materials to avoid cracking from earth movement AND any temperature differentials day to night. My question is regarding which of the three anti-crack and waterproofing membranes I should choose for a 6″ square marble and granite (alternating) stone surface with 1/8″ grout space. Also if a specialty type of higher level of polymer grout is recommended than the typical latex polymer dry bags from hardware stores?

        About concrete the slab: it is a clean well made install – with rebar internally and substrate appropriate amount of rock underneath and aggregate rock included in the mixture of concrete. It a slight angle for drainage, industry standard, as my installer was confident of that and skilled.

        I am installing a 24″ mosaic in the center of 1/8″vitreous glass tile, adhered to a 1/32nd” thick fiberglass mesh. I have used that in exterior and interior wet environments for 15 years, with no cracking, however – for this installation I am more concerned about the marble or granite , and even the grout, cracking over time.

        Please advise me on these questions:
        1. Which Anti-fracture and waterproofing membrane to use?
        a) Semoco or Redguard Paint on applied directly to Concrete?
        b) De-coupling Membrane (orange, 1/4″ square pockets, roll-on)
        c) Anti-fracture membrane (orange, roll on, 1/8″ thick)

        2. If IN ADDITION, I need to add an additional substrate? Such as:
        a) Hardi-backer that is Concrete Mortared to the raw concrete slab,
        adding the membrane recommend above, and tile on top of that,
        adhered with another layer of polymer Thin-set mortar.
        OR:
        Just apply an extra thick thick layer of polymer Thin-set or polymer enhanced concrete mortar, hashed so back-buttered so all the tiles adhere well? With 1/4″ – 3/8″ expansion joints between parts of the design every foot or two?

        Lastly, because of drainage and even with the slope – do you recommend a particular brand to grout and seal the patio with after it is grouted so it does not stain the white marble and white grout over time? I am concerned about discoloration from standing water or other elements.
        Thank you very much for your time and response.

        • Donato Pompo says:

          It is very important to properly prepare the exterior concrete patio substrate prior to installing tile over it. We do many investigations of failed exterior decks particularly on high-end homes where their natural stone or other tile is staining or failing in some way.

          The concrete slab should have a vapor retarder under it, but sometimes it is left out on exterior patios. It is important to prevent water/moisture from migrating up through the concrete to the surface of the tile. If there is no vapor retarder, then you need to waterproof the top as long as there is no hydrostatic pressure from water beneath the concrete slab.

          Note ever use Hardibacker board or any other backer board over a concrete substrate. It isn’t meant for that application, and it won’t allow the concrete surface to be adjusted to establish a slope. The concrete surface should be scarified and then a polymer modified patching mortar should be used to adjust the concrete substrate to the required height and so the surface is sloped away from the house towards a drain at the rate of 1/4″ per foot. This is important because you don’t want water collecting under the tile and being retained in the underlying mortar.

          Once the surface is properly prepared then you should apply a waterproof membrane. The liquid applied waterproof membranes are the easiest to install and they are more forgiving. I would not use an uncoupling membrane as they tend to retain water that cause problems. It is important that the surface of the waterproof membrane is sloped a minimum of 1/4″ per foot towards a drainage path so the water can evacuate.

          Use a polymer modified thinset mortar for adhering the tile to the membrane. Glass tiles require an ANSI A118.15 high-performance thinset. Do not use it to adjust the height of the concrete, as that should be done with a mortar bed or the patching mortar.

          I would use an ANSI A118.7 polymer modified cementitious grout. for better performance.

          You should install movement joints every 8 to 12 feet in each direction and at all transitions of joints particularly at perimeters adjacent to restraining walls. Use a closed-cell foam backer rod with a traffic grade ASTM C920 sealant as specified in the TCNA EJ171 standards.

          It is always best to use the installation products from a single manufacturer to ensure compatibility of products and so you can qualify for a labor and material warranty form the manufacturer.

  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.

  3. Aryana says:

    Hello,

    I commend you on your outstanding Q& Section, as it has SO much accurate and valuable insofmation. As it happens – I am a longtime mosaic artist in the SF Bat area with immacculate long time indoor and exterior tile installations using glass, marble, and ceramic. However – I am about to embark on a new type of exterior patio that I want to last longer than any of my previous projects. Money is no option.

    It is a NEW installation of 4-6″ thick well mixed concrete that has cured over 2 months. It receives partial direct sun. I am installing a ceramic tile edge, and 6″square white marble, and 6″ Square Obsidian Granite tiles in a design I created – with 1/8″grout spacing. In the center I am applying a 24″ circular mosaic of 1/8″ thick glass tile over a 1/32″ thick fiberglass mesh, which I have found to be appropriate for both interior and exterior mosaic durability. However, I believe that for longterm durability, with minimal degradation from weathering and UV – that I will choose a polymer grout for that.

    Now to my serious question, as I see it – and with my previous experience3 with concrete backerboard like Hardi-Backer, a solid waterproof concrete MAY be the appropriate subrstrate for my natural stone tiles. However, on the internet there is a lot of information regarding a silicone, or polymer paint on waterproofing and anti-fracture membrane such as the brand Semco. I also have used the (orange) anti-fracture roll-on membranes for exterior stone walkways in the past which are to this day un-cracked at all after 15 years of weathering and heavy daily use. So that is option 2, however, there is another square type of (orange) thicker membrane that I am unfamiliar with called a de-coupling membrane – so our of these three options, please can you assist me in selecting the most appropriate one? And as well, if I will need to concrete mortar and additional substrate on TOP of the raw concrete BEFORE the membrane, and tiling? I absolutely value your time and appreciate any information you have to offer, whether it is a text , email, or phone call.

    Additionally, I am also working to build my business and want to support any business that helps me satisfy my customers with the highest level of service, product quality and quality installation. For my future business development I can see us working together!

    • Donato Pompo says:

      It is very important to properly prepare the exterior concrete patio substrate prior to installing tile over it. We do many investigations of failed exterior decks particularly on high-end homes where their natural stone or other tile is staining or failing in some way.

      The concrete slab should have a vapor retarder under it, but sometimes it is left out on exterior patios. It is important to prevent water/moisture from migrating up through the concrete to the surface of the tile. If there is no vapor retarder, then you need to waterproof the top as long as there is no hydrostatic pressure from water beneath the concrete slab.

      Note ever use Hardibacker board or any other backer board over a concrete substrate. It isn’t meant for that application, and it won’t allow the concrete surface to be adjusted to establish a slope. The concrete surface should be scarified and then a polymer modified patching mortar should be used to adjust the concrete substrate to the required height and so the surface is sloped away from the house towards a drain at the rate of 1/4″ per foot. This is important because you don’t want water collecting under the tile and being retained in the underlying mortar.

      Once the surface is properly prepared then you should apply a waterproof membrane. The liquid applied waterproof membranes are the easiest to install and they are more forgiving. I would not use an uncoupling membrane as they tend to retain water that cause problems. It is important that the surface of the waterproof membrane is sloped a minimum of 1/4″ per foot towards a drainage path so the water can evacuate.

      Use a polymer modified thinset mortar for adhering the tile to the membrane. Glass tiles require an ANSI A118.15 high-performance thinset. Do not use it to adjust the height of the concrete, as that should be done with a mortar bed or the patching mortar.

      I would use an ANSI A118.7 polymer modified cementitious grout. for better performance.

      You should install movement joints every 8 to 12 feet in each direction and at all transitions of joints particularly at perimeters adjacent to restraining walls. Use a closed-cell foam backer rod with a traffic grade ASTM C920 sealant as specified in the TCNA EJ171 standards.

      It is always best to use the installation products from a single manufacturer to ensure compatibility of products and so you can qualify for a labor and material warranty form the manufacturer.

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