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Smart to tile outdoor over concrete?

Streamline | Posted in Construction Techniques on June 25, 2008 01:50am

I’ve got an outdoor patio (450 sf) that is now compacted gravel (several feet thick as it is used to backfill against foundation wall. I want to pour 4″ concrete patio over this 5/8 minus, cut some control joints after the pour, and sometime next year put on ditra and tile the patio. My questions:

1. Where I cut my control joints, and lay ditra over, will that present problems to my tiles above? That is, if there is a real movement at that joint, will ditra be adequate to protect the tiles from cracking above? I don’t know how much tolerance ditra offers. Should I even cut the control joints at all?

2. What to do with the concrete possibly shifting or drifting away from the house? is this even a concern. The patio is pretty much flat, but the adjoining yard is a little slope (1′ drop over 15′ grassy area). I would prefer NOT to drill into the foundation to hammer in rebars because the foundation has a waterproofing coat on it that I don’t want to pierce. Thoughts?

Thx.

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Replies

  1. Henley | Jun 25, 2008 03:42pm | #1

    Seams like a call to the Ditra people would be your best bet.
    Although if your slab did move considerably I don't see how a layer
    of plastic would protect your tiles.
    Don't know the true dimensions of your pad would be but
    21x21=441 sf would seam like it could use a control joint.

    Several feet of compacted stone. How long has it been there?
    How much water does it get?
    Mechanically tamped?

    Judgment call really.

  2. jrnbj | Jun 25, 2008 04:27pm | #2

    Save yourself years of trouble & expense and do decorative concrete, or good pavers. I suppose it's possible to do outdoor tile over slab and have it hold up well, but more often than not it's a maintenance headache. More so in a freeze thaw climate, but even in a dry climate it's a lot of extra work....

    1. User avater
      Dinosaur | Jun 25, 2008 08:07pm | #3

      He's in the Great NorthWet, so a dry climate he does not have. Dunno how often it freezes, tho.

      Your advice is good, but there is a way to get what he wants. The tile has to be set into the slab itself before the 'crete cures. Major PITA, tho. Lotsa flush scaffolding work and done leaning over and under deadline. I wouldn't want to try 450SF of that alone LOL....

      Dinosaur

      How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

      1. jrnbj | Jun 25, 2008 11:18pm | #4

        Nice to hear from you!!!
        Not sure that direct set tile would hold up any better than a good thinset job, though--and not sure good slab mud makes good setting mud, so to speak.
        Anyway, it's usually the grout that's the weak link (when it isn't a tile that doesn't stand up well outside to add to the headaches). I suppose an epoxy grout might improve your long term chances...
        Anyway, my main thought was that if you want a masonry deck (which I certainly would-even Ipe' wont last as long a stone-why not just find a paver you like.

        1. stevent1 | Jun 26, 2008 12:04am | #5

          Ditra is an uncoupling mebrane. You need a crack suppression membrane such as Noble CIS. Nothing will help for verticle movement or heaving.

           

          Chuck S

          live, work, build, ...better with wood

          Edited 6/25/2008 8:00 pm ET by stevent1

        2. TBone | Jun 26, 2008 12:12am | #6

          I'll second that. Get a good porcelain or similar vitreous tile and epoxy grout. Should lessen any cracking issues.

          1. jrnbj | Jun 26, 2008 12:22am | #7

            I was just suggesting his best chances for getting it done with some chance of success. Myself, you'd have to pay me big bucks to tile an outdoor slab--and I like doing tile.

          2. TBone | Jun 26, 2008 02:56am | #8

            Agreed, not the best idea...just seconding your recommendations.

        3. User avater
          Dinosaur | Jun 26, 2008 07:34am | #11

          Not sure that direct set tile would hold up any better than a good thinset job, though--and not sure good slab mud makes good setting mud, so to speak.

          Well, thinset is notoriously non-structural so the slab 'crete oughta be stronger. And if you can embed stone rubble in concrete for a foundation, I don't see why you can't embed tile in a slab and expect it to stay where you put it.  As for grout, yeah, that's the weakest part of a tile job. But I was thinking really embed the tiles flush in the slab, so no grout would be needed. Okay, maybe 'thinking' isn't the right word; 'fantasizing'...?

          LOL. Sounds like even more of a PITA than it did the first time. If anyone every pays me enough to try it, I'll let you know how it worked out!

           

          Dinosaur

          How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

  3. User avater
    ToolFreakBlue | Jun 26, 2008 05:24am | #9

    The control joints are to control the cracking of the concrete. It will crack, so telling it where to crack is the best approach.

    Let me throw this out there and see if it sticks to anything.

    What if you placed your control joints in reasonable locations and then tiled each of those areas without bridging the control joint. Put a good flexible caulk at that joint in stead of grout.

    (OH, the concrete may still crack someplace other than a control joint, but a tleast you tried to tell it where to crack)

    TFB (Bill)
    1. User avater
      BillHartmann | Jun 26, 2008 07:18am | #10

      That is exactly what the Tile Council of America suggest.Actually I think that they say to use a movement or expansion joint such as these.http://www.schluter.com/141.aspxbut I think that a caulked joint would also work..
      .
      A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

    2. Streamline | Jun 26, 2008 03:59pm | #12

      Thanks for your feedbacks. The gravel has been there for 2 years now and was mechanically compacted every 6" lifts. This room is actually an L shape outdoor room so the connections between the 2 rectangles would likely crack. Knowing that it will crack, perhaps it isn't a bad thing just to let it crack where it wants to (I can cut control joints to guide it, but why, since it will be covered with tiles anyway. After a year of cracking, I can place ditra on it, and tile over. Ditra will give me some flexibility as further cracking on the concrete takes place. I can place Schluter expansion strips where the two rectangles meet at the tile level. Isn't this a safer approach?A few of you mentioned pavers. I understand this to be non-grouted pavers where they just sit tight against each other and bedded on sand and jointed with sand. I was originally going there, but seeing how the sand can get into the house and killing my wood floor, I've opted for a cleaner tile surface where I can hose off without worrying about my joints coming loose. Is there another kind of paver that I am missing? thanks.

      1. jrnbj | Jun 26, 2008 05:43pm | #13

        No direct personal knowledge, but the new "polysand" used on pavers shouldn't track the way plain sand does. FWIW, go Japanese.....shoes off at door please. Simple life tip to help with American obsession with cleanliness.....

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