Tile is NOT Waterproof

by Roger

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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Jeff Rudisill


Please help with my condition of “cold feet” that extra socks won’t take care of.
We’re remoding the bathroom in our newly purchased, less than 2 year old manufactured home. Our intent is to provide an accessible bathroom for my wife, including a barrier-free shower. We’ve purchased a 60″ linear drain to be the “barrier” between the shower and the rest of the bathroom, and sufficient 12″ x 24″ porcelain tile to cover the complete floor and the shower walls up to the ceiling. The tiling pro is planning to start next week to install a cement mud-pan and float the shower walls in mud as the backing for the tiles. I’ve installed “purple” (moisture resistant) drywall on the shower wall studs in prep of the cement wall going in.

The floor joists are 2×6’s on 16″ centers; the bathroom sub floor up to the shower is one layer of 5/8″ OSB glued and stapled to the joists; the floor under the shower has been stripped of the OSB and replaced with 2″x10″ dry Doug Fir blocks on edge between the joists to provide a solid floor and reduce the height of the drain.

In preping to apply HydroBan on the sub floor in the bathroom section, I’ve read some stuff that now gives me “cold feet” about the entire job. First, I’ve read that HydroBan can’t be applied on OSB, but I’ve also recently read that the floor joists on such a job should be a minimum of 2″x10″ (the span is roughly 12 feet). I’m concerned that the floor is not structurally sound enough to support the mud and tile weight, and would appreciate your thoughts, even though you’re a “tile guy” and not a structural engineer. My backup plan is to coat the entire wall’s and floors with an elastomeric acrylic such as Metacrylic and coat that surface with an epoxy compound made to improve wear-life on the surface.



In a pickle…
Already had tile put on my shower walls….it is Ivetta Porcelain Tile Item # 0399383 with a rating of 5 PEI and impervious. The installer said we did not have to use a waterproofing material on the walls. He said we could but did not have too, he kept saying it would be fine and he does it all the time. So he just put the tile on the drywall. Another guy we talked to said he puts cement board on every single time, Red Guard (I think) and then the Tile. Should we have the tile ripped out and redone? We are into it for $1000 on the shower already.



I have ceramic tile that is 18×18 I had planned om using for the floor and walls in my shower. The box says 3-6%.
I have the floor mud bed complete and used Oatey shower pan. I took great care when I did the mud bed to make sure this tile would slope to the drain and still lay flat wth no voids since it is so large. For the walls I have used hardibaker directly to the studs and plan on using redgard.

1) will I see problems with this 3-6% tile on the floor or walls as long as I get adequate thinset coverage?
2) should the redgard be sealed down the wall and on to the floor a few inches or just stop at the bottom of the hardibaker? I’m leaving about a 1″ gap between the hardi and the mud bed.
3) should the floor tile go as far under the hardi on the walls so the the wall tile comes down on top of the floor tile? I would leave a 1/4″ gap and then silicone floor to wall gap

Thank you



Hi Greg,

1. No, coverage has nothing to do with the absorption rate of your tile. Provided your shower is properly waterproofed that rate makes no difference in a regular shower.

2. If you have the gap stop at the bottom of the backer.

3. It can go flush with the face of the backer so the wall tile sits on top of it. You don’t need 1/4″ – 1/16″ to 1/8″ is plenty.


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