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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  • Frank

    Does ceramic tile with epoxy grout still absorb water vapor? Installing a stem shower and deciding if I must use porcelain or if the less expensive ceramic glazed tile will suffice.

    • Frank

      Installing a steam shower

    • Roger

      Hi Frank,

      Yes it does. Always use porcelain in a steam shower. When you’re building a steam shower the small amount of money you pay for porcelain over ceramic is nothing, certainly not worth any problems that may arise from using the improper product.

  • Paul

    So why not just make tile and grout waterproof? This is the part i don’t get. Is it just in case water does get past your waterproof grout and tile so it has a way to evaporate or is there some other reason. I just had my tub converted to a walk-in shower and they used the kerdi system. That kerdi board seems like it will fail after awhile since water is going to be constantly hitting it. Plus the thinset they use for the seems isn’t waterproof so as small as that gap is water has a way of getting through places.

    • Roger

      Hi Paul,

      Because no one would be able to afford it. Hit google and price large format glass tile. Even with that, there needs to be area for vapor to escape – that’s why you don’t use epoxy grout with large format glass-the glass will crack.
      Pressure build up in and behind walls, it needs someplace to escape. When you have an open cavity with zero movement capability over it something’s gonna give. It will be your tile, every time.

      Water is constantly hitting the waterproof surface of the kerdi-board, which is foam (the board itself is foam, not the waterproof surface). Water WILL NOT (ever) change the physical shape or size of kerdi-board. It could conceivably wear it down, as water does with everything. However, that would require water be physically hitting it directly, which is why we tile over it. and the surface is waterproof. I’m not sure why you think it will fail, unless by ‘awhile’ you mean 100 years…

      Thinset does not need to be waterproof. Capillary action is limited in size (there needs to be enough space for the capillary action to take effect), thinsetting kerdi to something like more kerdi or kerdi-board eliminates that needed space. It’s waterproof. Really. If it wasn’t schluter would have been bankrupt 25 years ago.

  • Matt

    Cool article. But what about vinyl tile and grout for floors? Is it better than regular vinyl plank flooring? Which is more waterproof? Which can handle heavy dog traffic who on occasion get wet and muddy?

    • Roger

      Hi Matt,

      The only vinyl tile and grout of which I am aware is an armstrong product – is that what you’re talking about? And when you say ‘vinyl plank flooring’ I assume you are speaking of LVT (luxury vinyl tile)? In the case of those two the LVT is the better product, although neither is actually waterproof. As far as durability the LVT is much better.

  • Glenn

    What is best tile for a screened porch. I would like to use porcelain but does it have to be a special type of porcelain?

    • Roger

      Hi Glenn,

      Yes, porcelain is best. No, it doesn’t need to be any particular porcelain. If it’s porcelain it already has the needed absorption rating – all porcelain does.

  • Brett

    Hi Roger,

    Great site and article. I have a question about moisture traveling in the other direction. I have a newly poured concrete bathroom floor and I’ve been wondering how long to let it cure and dry before tiling over it. I’m wondering if I could create a problem if there is too much water evaporating from the concrete and accumulating under the tile. After reading this article about tile being porous, does it stand to reason that water vapor could safely evaporate from the concrete and escape through the tile and grout?

    • Roger

      Hi Brett,

      Minimum 30 days – minimum. That is if you are tiling directly to the concrete. If you use something like ditra you can do it in seven days, and the fact that there are air channels beneath the membrane eliminate ANY issues with moisture migration from the concrete.

      Moisture migration from concrete into tile assemblies normally manifests in the grout lines (path of least resistance). It will usually show up as efflorescence (white chalky substance on your grout). So yes, it will evaporate through your tile assembly, but it will do it through the grout, not the tile.