A common misconception about tile and grout is that they are waterproof. Once you install tile in your shower you have a big waterproof box that will last forever. Ummm, no.

Tile and stone (as well as grout) will actually retain water. How much water it retains is directly related to the density of the tile. For instance, porcelain tile is much more dense than travertine. This means that travertine will retain more moisture and allow more water to seep through  to your substrate. If you happen to have travertine in your shower – don’t panic. As long as it was installed properly it will be fine.

So how do they figure this out?

When a specific type or brand of tile or stone is manufactured for production, the company will determine its density. There are four different categories into which each tile may be placed.

This is determined by weighing the particular tile, submerging it in water for a period of time, then weighing it again. The difference in the two weights determines the density or absorption of that product. Basically how much water it holds. It will then be placed into one of the four categories.

  • Non-vitreous: These are tiles that absorb 7% or more of its body weight. These are for indoor use only, normally on vertical surfaces such as backsplashes and wainscots.
  • Semi-vitreous: These absorb between 3% and 7%. These are also for indoor use only.
  • Vitreous: Absorb between 0.5% and 3%. These tiles may be used for interior and exterior applications.
  • Impervious: These are the most dense (porcelain) and absorb between 0.001% and 0.5% of their weight in water. They are suitable for all applications.

Depending upon where you intend to install the tile you may need to consider this. In most cases it’s not an issue. Only in the most extreme or unusual circumstance will you need to take into account the category of your particular tile. A tiled patio in Alaska, for instance. If you have a tile that absorbs a considerable amount of moisture and it freezes, well, you’re gettin’ a new patio.

The biggest factor to consider is the amount of water to which the tile will be exposed. (Along with the possibility of freezing, of course.)  For anything up to and including a regular shower, it isn’t necessarily an issue. These applications, using proper methods, should be at least water resistant before a box of tile is even opened.

Why is this an issue?

With any tile application, the durability of the tile will be only as good as what is beneath the tile! Let me say type that again – that again.

If you have a wall in your shower with just plain drywall and you stick your tile to it, it may look good for about a year. It may look good for much longer. But, if moisture gets behind the tile (and it will) through the drywall, to the framing studs, well, you’re screwed.

Your framing studs are (most likely) just simple 2 X 4’s. If even a minute amount of moisture from your shower reaches it all hell’s gonna break loose. Common studs will do what we call “wick” moisture. It is aptly named because it acts just like a candle wick (tile guys are simple folk).If you place one end of a candle wick in water the other end will be soaked in short order. Wooden studs do the same thing.

Think of it as a water highway. The water will simply continue along that same path until it finds something else to soak into. That something else is more wood. When wood gets wet it . . . wait for it . . . swells. Normally that swell has only one place it’s going – right against the drywall and into the back of your tile. Tile’s will crack, grout will crack, your patience will crack, and the end of the world will be right around the corner. You get the idea.

This is not (normally) a subject that needs to be considered when installing tile on your floor. A shower (or other wet area) is unique in that it is subjected to a great amount of water on a regular basis. Unless your kitchen is a swimming pool you really don’t need to be that concerned about it.

Just understand that tile and grout are not waterproof so care needs to be taken to eliminate as much moisture from the surfaces as is realistic in any given application. You know – don’t make your kitchen floor a swimming pool.

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  • Jon

    High Elf… I have a small bathroom with sheet vinyl I want to remove, and lay down semi-vitreous ceramic tile (8 mm thick). The subfloor is plywood that was adhered to southern yellow pine (I think it is petrified now). After I clear off the vinyl, backing, and dried glue, should I use a sealer or put down plastic sheathing (as a impermeable layer) before I start the tile job. Thank you for all the helpful information.

  • MaryCatherine Rothwell

    I have a 1962 tiled shower. I do not have the money to do any remodeling right now. I think the shower leaks. Is there any commercial product that I can use to basically seal the whole floor of the shower to make it waterproof? I was reading about GacoDeck and thinking I could just paint the floor of the shower and seal it up to give me some time to save for a remodeling job down the road. Previous owner used some sort of plastic tape? and it is pealing up. Ive not even owned the house a year.

    • Roger

      Hi MaryCatherine,

      No, there is no product that will make an improperly built shower waterproof. I have no idea what gacodeck is, I know it’s not a product for showers. I have no idea whether it will buy you any time or not. Sorry.

  • Jan davis

    Hello! I would like to out a mosaic marble tile around the face of an outdoor fireplace (which is located under the cover of a patio).
    However, just saw that is says indoor use only- do you think this will be a problem? Live in Austin- not very cold during the winter months. Thanks!

    • Roger

      Hi Jan,

      If it’s marble it can be used outside.

  • Michelle

    Please help. We are havubg our bathroom remodeled. I ordered the Kerdi- schluter shower kit. I noticed that the roll of barrier that I’ve seen in many photos was not placed behind the shower tiles. They were put directly in the durock. The tiles were installed 3 days ago. What are my options? They only used the membrane on the shower floor. How hard is it going to be to get the tiles off and is that my only option? I have a photo which clearly shows no membrane.

    • Roger

      Hi Michelle,

      You can leave it and hope nothing goes wrong (not recommended) or you can have whomever installed the shower incorrectly come back, tear it out and replace it correctly. The tile will not come off the wall in one piece (unless they were incorrectly installed also), it will need to be replaced.

  • Norm Mosley

    Hi Roger. I’m putting in a tile shower and have done a lot of research on it. I do not want to have one of those “diy nightmare” stories. The shower is 40″x42″. I made my subfloor a good 2″ solid. Put down 2 layers of felt paper. Then put in the membrane. The concrete shower pan is 1 ½” thick at the drain (yes I used pea gravel around the weep holes) and about 2 1/4″ thick at the edges. A little too much slope but I wanted it that way. I’m ready to start laying tile, I think. I have 2 coats of Redgard on the walls and over lapped it on to the cement shower pan by two or three inches. I have a couple questions for you.
    1- is 2 coats of Redgard enough? I’m all nervous and stuff about water getting through.
    1a- is it possible to have too many coats on there? Will it affect tile adherence if there’s too much?
    2- should I Redgard the cement shower pan? If so, how many coats?

    • Roger

      Hi Norm,

      The thickness of the cured redgard should be about as thick as a credit card. There is a maximum thickness of the membrane, but I don’t know what it is. I know it’s ridiculously thick, like 3/8″ or so. NO! Do not use redgard over the deck if you have a membrane beneath it.

      Do you have a preslope?

  • Ming

    Again, thank you for such informative information. I’m having a hell of time finding a reliable tiler downunder. Or a good old tradie who is patient to explain. Not like I doubt about their skills, but I’m born with a curious mind, asking questions is just a way to learn.

    By the way, what you do does make a difference (ref: your bio), it makes lots of people’s life better, so they are happier! And I have learned a lot from your forum just by reading it. I can pass some of the information to my students in Australia. So, thank you.

  • gargey patil

    Hi Roger,

    We have a sunken master shower with porcelain tile and have had an unidentified slow, taking about 1year to develop, moisture leak to bedroom wood floor on the other side of the wall. The leak detection company could not find the leak. We replaced the damaged wood with 100% moisture resistant thin set glue. Now 2 years later, a new area of damage has emerged on wood planks beyond the repaired area. There is no shower pan, the angulation of the shower floor is decent, and there is special drywall behind the tile. Would you have any idea on the source of this leak? And any ideas for a solution without taking apart the shower floor?

    • Roger

      Hi Gargey,

      What the hell is “100% moisture resistant thin set glue”??? And what type of “special drywall”?

      The problem is that water WILL ALWAYS get behind your tile. If there is not a waterproof barrier of some sort there the water will find the path of least resistance. Before it was where you installed this glue, after it has moved past the glue, because it can’t soak or travel into your framing in that area. Now it’s simply found another path. Something in either your floor or wall is not properly waterproofed, the fact that it took 2 years to show up tells me it’s from water behind your tile, likely in the walls directly above or around the initial water damage.

  • Idris

    Is the main reason for sealing the grout of shower to make it easier to clean? If I am conifdent I have a waterproof substrate do I even need to seal?

    • Derek

      Even if your shower is properly waterproofed yes you still need to seal your grout. It does keep grout from absorbing water and helps fight off mold.although I prefer using two cotes and sealing every 1-3 years.

  • Harold Ball Sr

    Our tile installer placed a handful of thin-set one each end of 12×24 inch
    porcelain tiles and installed them on concrete backer board….resulting in an open space around the perimeter of each tile.
    Should I expect any resulting problems in the future?

    • Roger

      Hi Harold,

      More than likely. If there is open space beneath your tile there is a high chance that it, or the grout, will crack.

      • Tristan


        On mentioning “if your kitchen floor was a swimming pool”…. what about actually tiling a swimming pool? We have re-cemented the entry stairs (rest of the pool is vinyl), waterproofed, and just set stone tile on the surface and glass tiles around the walls. We have not grouted yet and we’re looking into epoxy grout (going to cost a small fortune). Do you have any recommendations for how to best seal tile that will be submerged under water all of the time? Will epoxy grout make a big difference vs a regular grout and sealing it somehow?

  • Paul

    My builder used a very porous tile on my shower floor. I have to scrub it every couple of weeks to remove black spots from water/soap/etc. I’ve sealed it more than a dozen times and the water from the shower keeps pitting the tile and creating new places that aren’t sealed and they just soak up the water and turn black.

    Is there anything you can think of to help besides ripping out the tile and replacing it?

    I think it’s either a travertine or a natural stone.

    • Roger

      Hi Paul,

      Travertine is a natural stone, but water should not do that to it. To give you a correct answer I would need to know exactly what you have in there.

  • Donald

    Hello , I had my bathroom remodeled and now the tiles inside the showers is leaking down into my kitchen what can I do to fix this problem

    • Roger

      Hi Donald,

      Apparently your shower was not properly waterproofed. I would call back whomever remodeled it and have it properly replaced.

  • Pat keoghan

    The best I have read in a long time. :lol: :-D :-D

  • clive carrinton

    I have an outside patio in the south France. What is the best solution to water proof the cement base before tiling it

  • Nicole

    Hi Roger,

    I am wanting to tile my bathtub surround with travertine tile; however, according to Lowes, this tile is Vitreous. Can I still use it as a surround? Or should I pick a different tile to use? I know you have said a sealer will only protect against stains, but if I properly waterproofed the walls behind the tile then used a sealer on the tile, will it be ok?

    Thanks for your help!

    • Roger

      Hi Nicole,

      Someone at lowes get a word of the day calendar or what? :D Yes, provided your substrate is properly waterproofed it will be just fine. You don’t even need the sealer if you don’t want it.

  • Nikitta

    Hi there,
    I’m looking at tiling the down stairs part of my house.
    The floors at the moment are concrete, I know I’ll have to water proof the bathroom but I’m looking at tiling the rest of the area (to turn into a granny flat)
    I know they aren’t naturally waterproof so I was wondering will they lift if a bit of flood water comes in over top of the area? Weather it be waterproofed or not?

    • Roger

      Hi Nikitta,

      Water isn’t going to affect tiles that are properly installed with thinset. It doesn’t have to all be waterproofed.

  • Clay

    Hello Roger,

    I am renovating my bathroom.
    Due to my shower leaking through the common wall to our bedroom and the wife wanting the bathroom updated.

    I’m in Perth Western Australia and the house is brick construction all internal walls are single fast wall bricks with concrete floors.

    I have removed everything from the bathroom.
    Removing tiles from the wall, removed cement screed and tiles from floor.

    I have noticed there was no damp course or waterproofing behind the tiles or over the hob in the shower.

    We had the house built in 1989 (local builder) so its lasted for a long time before leaking.

    When I ripped or jack hammered the wall tiles off the shower wall it removed the cement render. I had a tradie in to re render the wall yesterday.

    I know the tradie (cement render-er) did not mix any damp proofing material in with the cement render. (I now know he should have reading your previous comments).

    Q1. Do I now paint or apply a water proofing membrane to the walls and floor to waterproof the area before getting a Tiler in to lay the tiles.

    Q2. Can I paint or apply water proofing to cement render.

    The new HOB for the shower will be installed or done by the tiler, as the hob is placed in situ so the floor tiles are easier to lay or more importantly the Tiles fit better so there isn’t any small pieces of tiles.

    Q3. Should I just leave it and let the tiler waterproof the entire Shower area.

    I would prefer to email you a couple of photos to explain it better, but there doesn’t seem to be that capability here.



    • Roger

      Hi Clay,

      It would likely be best to let the tiler waterproof it, but you can apply a topical waterproofing like redgard, hydroban or kerdi.