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No underlayment for ceramic tile?

jdarylh1 | Posted in Construction Techniques on November 3, 2005 01:00am

There’s an area about 6′ x 8′ in front of our front door that has 8″ x 8″ ceramic tile on it. The ceramic is level with the carpet which tells me that it was applied directly to the OSB without any additional plywood underneath. I should pull up a corner of carpet to be certain, but I’m 99% sure that’s the case.

We’re the third owner…I don’t know when the tile was installed, but we’ve been here 4 years and there isn’t one bit of cracking. There’s another area upstairs that’s 3′ by 18′ with the same situation and no cracking. I always thought you had to put down some form of underlayment over the OSB before tiling.

I’m just about to replace the carpet in our 2 small bathrooms with ceramic. Based on what I’ve seen on the other tiled areas here, it seems like I can put the new tile down directly on the OSB with no problems. I’m sure that would be quite risky if I used marble, but should I be OK with ceramic?

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Replies

  1. MikeSmith | Nov 03, 2005 02:05pm | #1

    think about ditra...

    Mike Smith Rhode Island : Design / Build / Repair / Restore
    1. User avater
      AaronRosenthal | Nov 22, 2005 04:22am | #24

      Ditra? Did I miss something?
      I was under the impression that ditra is great (it is), but you needed to have a solid substrate just because of the weight of all that stone.
      Did you suspend the laws of physics on me again, Mike?Quality repairs for your home.

      AaronR ConstructionVancouver, Canada

       

  2. piko | Nov 03, 2005 05:12pm | #2

    Tile would be abt 3/8" thick - carpet with underlay abt twice that...go ahead and lift a bit of carpet to be sure. As for the new work - make sure you do it right, even if it means a transition strip at the thresholds and taking some off the bottom of doors. That something has lasted well doesn't mean that future work will, but because it has lasted indictes it was done right.

    All the best...

    To those who know - this may be obvious. To those who don't - I hope I've helped.

     

  3. fingers | Nov 04, 2005 12:48am | #3

    I may be going out on a limb here but, yes you can use ditra or some kind of underlayment, but my understanding of tile installation is that the most important factor is the solidity and stiffness of the floor.

    A friend of mine who installs tile daily says that tile will stick to almost anything more or less permanently if the substrate is flat and stiff.

    That translates into "no deflection when a load is placed on the floor".  Of course there's no such thing as "no deflection" but you know what I mean.

    Good Luck!

  4. WayneL5 | Nov 04, 2005 03:37am | #4

    You can get by with tile on a wooden substrate when the environment is dry.  It was common practice 20 years ago before cement board was available and the only alternative was a 2" thick layer of concrete.  But in a bathroom the water that splashes around all the time will, in seconds, soak through the grout and dampen the wood below.  If it happened daily you'd soften the OSB.  You could get a number of years out of such a floor, but not a truly reliable one.  Also, under the toilet where you had cold porcelain in contact with the tile combined with poor air circulation you'd almost certainly have long term dampness and it would rot.

    Skipping cement board would be asking for trouble in a bathroom.

    1. jdarylh1 | Nov 04, 2005 12:42pm | #6

      I didn't think about water soaking through the grout to soften the OSB. Or problems with cold porcelain. Good points. OK..I'll hunt up some ditra AND seal the grout. Never heard of ditra, I assume it's some kind of cement board? Hope it's thin stuff. I've never been fond of the looks of a built-up floor even if there is a nice transition strip.Just thought of something...as an alternative, could I coat the OSB with deck waterproofing instead? Or marine polyurethane? Or oil based paint? Not trying to get out of the work or cost of ditra, just trying to avoid the buildup.

      1. FastEddie | Nov 04, 2005 03:00pm | #7

        Ditra is about 1/8" thick.  Comes in rolls about 4 ft wide (or is it 5 ft?) by as long as you need.  Cuts with scissors or a sharp knife.  Most tile stores have it.

          

        "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

        1. jdarylh1 | Nov 05, 2005 12:59pm | #12

          If Ditra is 1/8", that's nothing. I'll use it without a second thought. Since the floor area in each bathroom is about 20 sq. ft it won't amount to anything cost wise.

      2. WayneL5 | Nov 05, 2005 03:54am | #10

        Coating OSB won't work.  Anything that will repel water will repel thinset mortar.

        Ditra is a plastic material that has a waffle like pattern.  It is designed to be used over a floor that is stiff but cracked, like a concrete slab.  It keeps cracks in the slab from telegraphing through to the tile.

        I have heard it is expensive, but I've never used it.

        1. FastEddie | Nov 05, 2005 04:21am | #11

          I have heard it is expensive

          It's only expensive if you don't use it, and the tiles crack.  :)   About $1.40/sf 

          "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

          1. CJD | Nov 05, 2005 05:21pm | #13

            Is $1.40/Ft² installed of for the Ditra material alone?

            I have a 2nd story, interior, hydronically heated, R-25 insulated, concrete floor that is 34' square that I plan to tile. I am looking for a good product to uncouple/isolate slab for tile crack prevention. Ditra seems like it is more than necessary since temperature isolation and waterproofing is not needed. Any thoughts?

          2. FastEddie | Nov 05, 2005 08:30pm | #14

            That price is out the door at the tile shop.  The labor is free if you do it yourself  :)

              

            "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

          3. kevreh | Nov 11, 2005 05:28am | #17

            Ditra would work well for your situation. I've used it a couple times and think the stuff is the best.... its' German engineering helps too :o)If its 2nd story, the cement floor is floating over joists? If so, you'll still need to factor in deflection. I'm guessing the floor is plenty stiff to prevent cracking.BTW, you can buy ditra online here:http://www.tile-experts.com/products.asp?id=47Kevin

          4. CJD | Nov 20, 2005 06:33pm | #20

            Kevreh:

            The 2nd story deck is cast in place Lite-Deck — 10" beams on 24" centers topped with 4" slab for a 14" finished beam thickness. There are two #5 Grade 60 rebars at the bottom of each beam and a 12x16 rebar mat on top. The deflection under residential dynamic loads is nearly immeasurable.

            Thanks for the info.

        2. BillBrennen | Nov 11, 2005 08:29pm | #19

          WayneL,You said, "Coating OSB won't work. Anything that will repel water will repel thinset mortar." This is actually false. There are several liquid waterproofing systems that can be tiled over with thinset, prime example being Red Gard, sold at HD. Red Gard is also rated as an isolation membrane, when applied according to the directions on the bucket.That being said, the Ditra still seems like a better system over the OSB, since it can accomodate more movement.Bill

          1. Scooter1 | Nov 25, 2005 09:45pm | #29

            I'm not as big of a Schulter fan as most around here. I'd use any pvc antifracture membranes--about a 16th of an inch, and cheaper than Ditra and easier to install.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934

          2. jdarylh1 | Nov 26, 2005 02:38pm | #30

            Could you tell me more? I'm not familiar with the pvc membranes. Do you have any brand names I can look up? Do you have to go to specialty tile stores to get it or do HD & Lowes carry it?

          3. Scooter1 | Nov 27, 2005 02:00am | #31

            Yes, you will have to go to a masonry supplier or Tile Store, such as DalTile. The brand names are Nobel, Pasco, and Compolite, that I have used, but there others. They run about $2-3 per foot, about half the price of Ditra, and don't cup or have to be weighted down like Ditra does.These membranes are only about a 16th of an inch, and are covered with a while fleece which assists the tile to bond with membrane. The membrane is, in turn, bonded to the substrate.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934

          4. FastEddie | Nov 27, 2005 02:09am | #32

            about $2-3 per foot, about half the price of Ditra

            Let me sell you some ocean-front land in Arizona.   My tile store sells Ditra fo0r about $1.50/sf.

            I used the DalTile brand of Nobleseal (only diofference was the color) and I had a little problem with it trying to curl.  I think it is sold mainly as a waterproofing membrane, but they do admnit that it help with crack control.   You're right on one thing ... it is a lot thinner than the Ditra.

              

            "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

          5. jdarylh1 | Nov 28, 2005 01:50am | #33

            Thanks. I'll check it out.

  5. User avater
    Dinosaur | Nov 04, 2005 05:36am | #5

    I'd recommend the same thing as Mike--think about using Ditra. It's easy to use, and for a small bathroom the extra cost won't be a big percentage.

    Yes, I, just like most others who've been around long enough, have laid tile directly over plywood, and gotten away with it. But OSB is another animal entirely. I wouldn't take a chance on it, especially in a wet area, no matter how well your foyer has held up.

    Besides, 4 years is nothing in the life of a tile floor. The one in my grandmother's bathroom had  lasted well over 60 years with nary a crack in it when the house was finally sold in the 80s.

    Of course, the tile was laid over a full mud bed on the subfloor and it was 1" hex tiles. No dummies, those old-timers....

    Dinosaur

    A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...

    But it is not this day.

  6. pickings | Nov 04, 2005 06:00pm | #8

    You only have to "redo" ie, tearout and replace ONE tile job to want to do it right in the future.

    What works in the foyer is not relevant in a bath. Apart from actual water, baths are a lot more humid. Tiling a bath w/out an underlayment is begging for trouble. As stated here....the life expectancy of a tile floor is about 50 years. (OSB-???)Depending on your age, you should not have to tile the same area twice.

    If you are really worried about "buildup".....I have had success w/ 1/4" thk hardibacker before. Adds an evening to the job...but compared to 50 years....

    Have not used Ditka, so I can't comment on it. Personally, I like a stiff floor for tiles.

    1. FastEddie | Nov 05, 2005 02:48am | #9

      Hardieboard does not make the floor stiffer.

      And Kilz does not kill mold.

        

      "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

      1. pickings | Nov 07, 2005 05:41pm | #15

        "Hardieboard does not make the floor stiffer."

        Even when screwed down over thinset? Have used the 1/4 " and the 1/2" in different baths over 1x6 t&g sub-floor, and after they were laid the floor felt a lot stiffer to me.

        Maybe they don't do much for a plywood sub-floor???

        1. kevreh | Nov 11, 2005 05:23am | #16

          It will make the floor stiffer between joists, but not overall when you think of the subfloor being supported by the joists. You need to do a deflection calc:http://www.johnbridge.com/vbulletin/deflecto.plKevin

          1. pickings | Nov 11, 2005 05:39pm | #18

            "It will make the floor stiffer between joists...."

            My thoughts exactly. Have not run into many bath floors (typically have been small) that deflect enough to warrant a framing "beef up", but then again, I don't do that many, only 1 or 2 a year.

             

  7. Wango1 | Nov 20, 2005 08:24pm | #21

    I think we are all missing the most important part. OSB is not to be used with ceramic tile. According to the Tile Council of America handbook, OSB is forbidden in tile setting!

    That said, the only two companys that will warrant it's use is Hardibacker and Ditra. (And I'll bet even they don't want to but realize that if half the houses nowadays are being built with OSB, they get a larger market share.) The TCA also states that a floor over joists should be 1 1/4" thick before tiling. (3/4" plywood sub and 1/2" CBU) and always set in mortar. How Ditra gets by this is it is an isolation membrane and allows the floor to move independant of the subfloor.

    Most installs need to have a 1/360" deflection over the span of the floor. (i.e. a 15' wide room = 180" divided by 360= 1/2" total flex. Stone materials usually require a 1/720", or half the previous or 1/4".

    You can find Ditra at Schluter.com 

     

    1. jdarylh1 | Nov 21, 2005 02:20pm | #22

      Thank you. I'm going to look around here for it but if I can't find it, I'll call Schluter.

      1. Wango1 | Nov 22, 2005 03:24am | #23

        I'm a trainer for HD here in WI and our district recently started carrying Ditra. A 54 s.f. roll goes for $69. Let me know if you can't find it.

        1. jdarylh1 | Nov 24, 2005 03:59pm | #25

          That's great to know! When I get to my tiling, I'll check the HD's around here. Right now I'm in the middle of some wiring.

  8. JRuss | Nov 24, 2005 04:38pm | #26

    One additional subfloor thought, that does not alter the previous good advice. I've seen some subfloor applications especially at entrance areas, where the 3/4" was cut out and a 1/2" piece was applied to accommodate a "backer" in the limited tiled area.  I've even seen the joist notched for that reason.  The carpet pull back should reveal all.

    Never serious, but always right.
    1. jdarylh1 | Nov 25, 2005 03:57pm | #27

      >'ve even seen the joist notched for that reason.<Now that's a heck of an idea. Lot of work, but that way you could get 1 1/2" of support before putting down marble or whatever and still keep it even with the other areas. Any ideas on whether or not it would pass an inspection?

      1. JRuss | Nov 25, 2005 06:32pm | #28

        Where I have seen it was in some townhouses we renovated. I assume it did, once the backer or tile is down, who would know. Actually I don't think there was a span or strength issue anyway.Never serious, but always right.

    2. JohnSprung | Dec 02, 2005 02:51am | #34

      Another approach is to pull the subfloor, nail cleats to the sides of the joists 1 1/2" down, then drop two rips of 3/4" ply between the joists on top of the cleats.  (Of course glue and nail the living s--t out of all this.)

      That gets you a solid surface at the level of the tops of the joists, without compromising joist depth.  Backer and tile from there up, and you can come real close to whatever adjacent floor surface level you want to match. 

       

      -- J.S.

       

      1. jdarylh1 | Dec 02, 2005 02:15pm | #36

        Now that's slick as heck also. I'm thinking deck screws instead of nailing though. Probably ought to glue the 3/4 to the cleats to eliminate future squeaking.

        1. JohnSprung | Dec 02, 2005 10:10pm | #38

          The downside to this is it's kinda labor intensive.  You have a lot of cleats and ripping to do.  If you go for it, make yourself a couple saddle-type jigs or gauges to get the cleats positioned quickly and accurately.  (The gauge is a sort of upside-down "U" shape, to fit over the joist top.  Hold it down with your knee while you pull the cleat up snug against the bottom of it, then shoot a nail.)

          Yes, glue everything.  Glue and nail the cleats to the joists.  Run glue on top of the cleats before you drop the first rip in.  Glue between the two rips to make it more like one piece of ply.  Good quality deck screws are fine instead of nails, but again more labor intensive. 

          Squeaking will not be an issue -- at least not until after a massive failure of the tile.  Enough relative movement to squeak would be far more than enough to make big cracks all over the place.   

           

          -- J.S.

           

          1. jdarylh1 | Dec 05, 2005 02:03pm | #39

            Good idea on the jig. Screws vs. nails - no shear concerns, so the advantage with screws is that they would pull the cleat tight, while the framing nailer would be faster. Toss-up I guess. Thanks for the advice.

  9. butch | Dec 02, 2005 03:01am | #35

    are you sure there isn't anything under the carpet?

    back in the olden days anything that got carpet got

    a layer of particleboard.

    That might be the reason the carpet is even w/tile.

    1. jdarylh1 | Dec 02, 2005 02:17pm | #37

      So OSB went down first, then particle board? I haven't looked yet but I'll keep that idea in mind. You can clearly see the OSB from the basement so I know it's underneath everything.

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