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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Sue Auerbach

Hi- I just installed a 1×1 tumbled marble mosaic tile floor in a bathroom. The floor always looks wet, even days after a shower. This isn’t an issue in the shower, where it has a rubber liner under it. The rest of the floor also looks wet but now we are getting moisture issues at the wood floor outside the room. We also have a bit of mold at a joint where wall meets floor (both tiled).
Our belief is that the water is seeping through the floor (it has been well sealed), and running under the floor. If we get the water to dry, what can we put on the tile and grout to prevent this issue from continuing or getting worse??

Thanks for the help,
Sue

Reply

Paul

Hey roger,
Similarly to some of the above questions: Do I need to remove my tiles?
I ripped out a vinyl tub/shower to the studs, installed a steel/porcelain tub, cement backer boards, mortared and tiled. In the process, I got ahead of myself and didn’t apply the waterproofing to the walls before tiling. Do I need to remove and start over with the waterproofing first or are the walls sufficient as they are now?

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Victoria

Hi, I’m really hoping you can answer this question since every time I ask someone, I get a different answer! I want to use a 16 x 32 tile on all three sides of my shower/tub surround, and continue it to the end of the 3rd wall. It is a white body wall tile that has a 3 dimension effect to it. The tile is half inch and 8.5mm. The catalogue says the water absorption rate is 10%-20%. The company says that it can go in a wet shower environment no problem. It just can’t be submerged in a pool setting. From my online research, I thought that the water absorption rate should be less than 3% for showers. Do you have any ideas on this? Thanks so much for any advice!

Reply

Roger

Hi Victoria,

Unless you are installing it in a steam shower (which would infuse vapor into the tile) a tile with a high absorption rate is not a problem. If your shower is properly waterproofed you can place nearly any type of tile into it. Regular clay-body ceramic tiles used to be close to 25%. We would actually soak them in water before installing them. :D Your tile is fine.

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Victoria

Wow…you made my day! Thanks for the info—I feel better about using this tile now :)

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Victoria

Actually Roger, can I ask one more? :)

This tile has a 3D effect to it…it has a raised wave pattern in it.
It’s going on all the walls of my shower.
Some people say it can’t be used on the shower fixture wall because the silver plates of the fixtures won’t lay flat on it.
Other people say that the tile itself is waterproof and the plates are just for show, so it’s fine if they don’t lay flat.
Others say that I should silicone around the plates (using more where the tile is lower in the wave) to make sure it is waterproofed.
Others say I should cut out the tile and recess my plate into the tile.
Others say I should cut out a flat tile in a square and put all my fixtures on the flat tile, and then cut out the wave tile around the flat tile and fixture square.
Any ideas one if this is doable…hanging fixtures on a wave tile while still maintaining waterproof conditions?
It’s the ribbon tile on this page:
http://www.atlasconcorde.it/en/collections/marvel-pro-wall-design/decori/statuario-select/shinyrettificato/

Thanks again!!

Victoria

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Karen

Hi, We just DIY installed our mud shower pan over a professionally hot mopped shower pan. We thought it would be a good idea to test the slope of the pan by pouring water over it to watch if it pooled anywhere. Much to our surprise, all the water was quickly absorbed by the concrete pan. Is this normal? The mud/concrete ingredients that we read up on and used included quite a bit of sand. We used pea gravel around the weep holes and it seems like we followed all the rules. Thanks, Karen

Reply

Roger

Hi Karen,

You did follow the rules – it’s supposed to do that.

Reply

Melanie

we renovated our new 100 year old farm house with the help of a contractor. He got a tile guy to come in and put the tiles down in our bathroom floor and the walls in the bathtub. We noticed after he was done that he used one floor tile on the wall in the shower, the rest of them have a gloss on them. We have tried to get a hold of him to ask him about it but haven’t heard back yet. Will the one floor tile make a difference? Can we still shower and leave it as is? Or should we call him back and ask him to fix it.

Reply

Roger

Hi Melanie,

It’s not going to hurt anything, but I would definitely have him replace it, simply because it’s not right. It will not compromise your shower at all.

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Rhonda

We have bought an old house built in early 1900’s the bathroom looks like it was remodeled in pieces from the 70’s and possibly recently but I want to redo the shower surround in tile they just used a plastic surround do I need to rip it out to the studs and just install the hardibacker board to place my tiles?

Reply

Roger

Hi Rhonda,

Yes, the plastic surround needs to be removed and backer put up.

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Matt

Hello,

I think I’ve made a blunder. I ripped out the tile in the walk-in shower, which is built on a slab. I then put up felt paper on the studs, followed by hardibacker, then mortar and tile. I did not apply Red Guard or any other waterproofing sealer to the hardibacker (I didn’t come across recommendations for it in the DIY tile books I bought from the big box store). I put up porcelain tile and am using Quartzlock 2 for grout. I haven’t yet done the bottom row of tiles or the tiles for the floor of the shower (slab). I was going to waterproof this with Red Guard (or something like it) and then go up the walls a few inches. Will this not matter and am I likely screwed anyway?

Thanks for any advice you can offer,

Matt

Reply

Roger

Hi Matt,

You need to use some type of liner in the floor which can be run up the walls and lapped BEHIND the felt paper. You can not use felt paper with a topical membrane on the floor. Water running down the wall will always end up behind your waterproofing on the floor, it defeats the purpose. You need to build a traditionally waterproofed floor with a rubber membrane.

Reply

Rodolfo

I am redoing a shower. The floor is concrete then there is a thick plastic shower pan followed by sloped cement/concrete. Can I break off the floor tile, scrape and smooth then apply red guard, thinset and tile. I’ll be tearing the wall down, which have greenboard, and installing hardibacker, which book do you recommend to get the most waterproofing

Reply

Roger

Hi Rodolfo,

You can, but you’ll have trouble tying into the drain. It would be best to remove the deck as well and start from scratch. If you’re using redgard then this is the one you want: Elastomeric membranes for shower waterproofing.

Reply

charles brown

After many years, we are draining swim pool and simply overlaying grout in between the tile spaces (but not replacing the tiles) to improve color/look.

Is it alright to use ordinary grout or should we use special sealant grout?

Reply

Roger

Hi Charles,

Regular grout is just fine to my knowledge – but I’m not a pool guy. I would check with the manufacturers to ensure the chemicals won’t negatively affect the grout.

Reply

Garth

I’m thinking of installing VCT (Vinyl composit tile) in a 2nd story laundryroom. I’m most concerned about water and mold resistance. I like the VCT mostly becuase of the retro look and colors. Do you think this is a bad idea – what can go wrong? If we do this – how can we maximize the possiblity of it lasting a very long time and resisting some water here and there from regular laundry room type things. Thanks!

Reply

Roger

Hi Garth,

Properly installed vct is not affected at all by regular water exposure.

Reply

Jeff Rudisill

Roger,

Please help with my condition of “cold feet” that extra socks won’t take care of.
Backstory:
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.

Reply

Roger

Hi Jeff,

All real tile guys have to become engineers to a point. :D The single layer 5/8 over your 2×6 joists is not sufficient, you need an additional layer of plywood over that to a minimum 1 1/8″ overall thickness. If you do that your bathroom floor will be sturdy enough, but you still need a proper tile substrate, like cement backerboard, ditra, greenskin, etc. The bare osb or wood, even with hydroban over it, is not a sufficient bonding surface for your floor tile.

Reply

Jeff

Thanks Roger,

Update: we ripped up the OSB and replaced it wimth two sheets of 19/32 exterior glue plywood, subfloor perpendicular to joists and underlayment perpendicular to subfloor. Upon checking in the crawspace under the floor, turns out there’s another steel beam 4′ from the centerline, so the span of the 2X6 joists is only 8′, which produces a deflection suitable for ceramic (porcelain) tile.
The tile pro floated the pan with cement and installed a PASCO membrane on the entire floor, shower and bath room. The shower’s been leak tested, and he’ll mud the bathroom floor to slope to the drain before he lays the tile. Looks like everything’s ok, unless you have other suggestions.

Reply

Roger

Sounds fine to me.

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Josh

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.

Reply

Roger

Hi Josh,

Unfortunately yes, it should be replaced. The first guy didn’t know what the hell he was talking about (obviously).

Reply

Greg

Roger,
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.

Questions
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
Greg

Reply

Roger

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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