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Maximum tile size for shower floor

March 6, 2012

My shower floor is 4' x 5' with a Kerdi drain in the center. The floor is sloped 1/4" per foot from the drain to the furthest point.

I'm thinking about using slate on this shower floor and I have received conflicting advice regarding the tile size. Some have advised not to go larger than 4" x 4", while I have also heard that I can go as large as 12" x 12".

From what I've read, the smaller size is recommended for two reasons. One, it will allow for more grout which will provide traction. But, slate has texture so perhaps extra grout for traction is not needed? Second, smaller tiles will make it easier to tile the sloped floor. But, with a 4' x 5' floor, could I make larger tiles work?

If I try to use larger tiles, is there a recommended layout which will allow this to work? And, is using slate on the shower floor going to result in maintenance problems down the road (eg water sitting in the crevices, etc)?

Comments (15)

  • MongoCT

    You have both issues well in hand.

    It's a matter of traction; the slicker the tile, the smaller you want that tile to be so the grout lines will afford traction, and

    It's a matter of conforming to the shape of the slope; smaller tile can conform to "twists and turns" of any changes in slope without creating lippage between adjacent tiles.

    I've done shower floors in mosaic, I've done conventionally sloped shower floors using just four slabs of material, one for each quadrant.

    With small tiles you can create a patternless sloped "bowl" of sorts on the shower floor, the breaks in slope are pretty much indistinguishable within the tiled floor. The floor I did with one slab for each quadrant? There were four very distinguishable cut lines in the floor running from each floor corner to the drain.

    So there are pluses and minuses, but as silly as it sounds, it depends on what you consider to be pluses and what you consider to be minuses.

    Much also depends on how your existing slope is shaped. Does your floor have defined breaks in the slope from corner to drain? Can a 4" tile, a 6" tile, a 12" tile that is simply dry set over that change in plane, will the tile sit "okay" or does it rock excessively since you have a flat tile sitting over a non-flat surface? Any excessive rocking will result in lippage, the inability of the edges of the rocking tile to properly mate up with the edges of the neighboring tiles.

    So "how big can you go?" You can go as big as you can go until you can't go any bigger. When the tiles rock, you're too big.

    If your mud slope has well-defined breaks in the changes of plane that run from corner-to-drain, then you can go as large as you choose if you incorporate cut lines in the tiled floor at those four corner-to-drain break lines.

    Do be careful with "slate" on a shower floor. You really need a tight grained stone, or the floor could turn into a putrid mess over time. A high quality true slate can perform well on a shower floor. Unfortunately much of what is sold today, especially in the form of natural cleft slate, is far from high quality.

    Honed slate will generally be a better quality slate, the stone has to be good quality to survive the honing process.

    There are some very good faux-porcelain slates being manufactured today. They might be worth checking out if the cleft look is what you really want. You may give up a little on looks and naturalness, but you'll potentially gain a lot in terms of durability and maintenance.

  • jaidog


    Thanks for your detailed explanation. I will lay the large slate tiles in the shower and check for rocking.

    As far as using slate in the first place -- we have had this slate tile sitting in our basement for a few years with no opportunity to use it. We are now trying to incorporate some of it into our master bath shower, with hopes of using the rest in other portions of the bathroom in the future. I almost feel obligated to use it since it is essentially "free" and has a nice color/texture. But, I don't want to use it in the wrong spot (eg shower floor) if it will cause problems down the road.

  • Dando

    cut the tiles you have if they are too large

  • pricklypearcactus

    Thank you for your very detailed explanation, mongo, especially the part about checking for "rocking". When I (eventually) get to redo my master bathroom, I was wondering how I would know the right size of tile. This was very helpful.

  • PRO

    As a general rule, 6x6 tiles are about as large as you can do in a conventionally sloped shower. Even then, you may get some issues. It will cost more to have a pro do the quadrant slope that Mongo mentions, (it's a bit trickier to accomplish) but it is a great look for a modern bath. Another choice would be to slope the entire floor in one direction only and use a trench drain. You could use one single slab of (flamed or honed) stone for that, but it would be a headache logistically.

  • jaidog


    The shower pan has already been poured. I've laid some tiles down on the pan and there is significant rocking, so I am going to go for the 'traditional' 4x4 or smaller tiles.

    Regarding the trench drain, I wanted to use a trench drain and build a curbless shower, but backed off due to the cost of the trench drain and floor height issues. Just read a post by Bill Vincent stating that Laticrete has a less expensive trench drain in the works, and realized that my floor is naturally pitched allowing for a trench drain without any structural modifications. If I hadn't already poured the pan, I would go down this route. But, now it's too late.

  • aspentexan

    i have a 3/4" square glass mosaic tile, would it prove to be too slippery to utilize as the floor in a walk-in shower?

  • PRO
    Cabot & Rowe

    Not slippery at all. The grout will provide traction

  • nicole___

    Slate.....OK....lets talk slate on a floor. My neighbor put down slate on his entire first floor and has regrets. It's uneven, hard to keep clean, hard to walk on.....ever tried walking on an uneven surface....it's very unpleasant. Now imagine putting that on a shower floor.

    I do my own tile work and used 2" slate on a pinwheel pattern on a bathroom floor. When walking on it barefoot you can "feel" the slate tiles....they're different than the ceramic....almost bumpy.

    Cutting slate. The cut edges will be sharp. You would need to file ALL the cut edges to use them on a shower floor. The labor alone to do this "right" would be huge!

  • PRO
    Creative Ceramic & Marble/ Bill Vincent

    Even with a traditional pan, there IS a way to use larger tiles, but the pan has to be planned with that in mind, and the drain pretty much MUST be centered. The way it's done is the pan is made up of 4 flat planes, broken by a diagonal line from each of the four corners of the drain to each of the four corners of the showers. A continuous joint is then made along those four lines, and what you end up with is four flat "panels" on the shower floor, and the ability to use a larger tile, being that you're using flat surfaces to set your tile on.

  • PRO
    Ironwood Renovation L.L.C.
    We are doing a double shower with two drains using pre-sloped pans.
    The tile is a 3.5 hex and the home owner does not want quadrant grout lines.
    To solve the lippage issue we have to re-shape the two pans and build up a skim coat of thinset.
    The hex tile is on the fringe of being to large for 3ft. x 3ft pan and the peak where two pans meet in middle require extra care.
    A 2in to 2.5in. would be an ideal size in our scenario.
  • PRO
    Creative Ceramic & Marble/ Bill Vincent

    What about a single straight grout line at the peak between the two showers, and then slope each shower from there?

  • PRO
    Ironwood Renovation L.L.C.
    BV - we had the discussion about a grout line at peak where shower pans meet.
    The home owner rejected that idea and agreed to live with a little lippage.
    Looks like I will be doing more skim coat today - I'll post a photo when it's done.
    Kind of a wish and a prayer - nothing worse then a client who decides after the fact that it wasn't the best decision.
  • Mrs Pete

    I'd go as small as reasonably possible. Smaller = less chance of slipping. I have 2" in my current tiled shower ... and I'd like 1". I would not go bigger than 4" personally.

  • PRO
    Creative Ceramic & Marble/ Bill Vincent

    Ironwood-- I hate it when that happens!

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