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Discussion Forum

Underlayment Gaps between the sheets

| Posted in Construction Techniques on May 24, 2003 05:13am

What do the floor guys think about 1/8th to 1/2 inch gaps between and around the sheets. Leaving it loose definitly cuts down on the installation times. Your measurements don’t have to be perfect , and you don’t have to keep cutting because you measured too tight. i guess the 18th is for expansion which i find questionable anyway since , thinset fills in that gap anyway. which actually in my mind could do more harm than good. if the sheet expands or shrinks against the mortar, It isn’t going to give.

1/2″ cdx under ceramic tile with at least an 1/8th inch gap, is that typical. It looks like

. I just wonder if any other floor contractors worry about it for a technical reason?

Where there’s A wheel there’s a way, got any wheels?

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  1. GHR | May 24, 2003 05:47pm | #1

    The 1/8" gap is to allow size changes during construction.

    If the sub flooring is glued in place or in your case tile is placed over it, the gaps are not neeeded for long term expansion control. (think about all of the 3/4" T&G sheathing that is glued along all of the edges)

    1. Edgar76b | May 24, 2003 07:19pm | #2

      Thanks George, I think I know what you mean but let me say it back to see if i got it.

      The gap isn't for long term expansion, it is for epansion that might occur before the tile goes on, in some cases a few weeks.

      I am working on a finishe crew . we are also doing underlayment kitchens and baths. But we don't nail in the field. just the perimeter of each sheet about every foot.

      I guess the floor installer comes along and nails it home before the thinset goes down. I hopes so. At that point its not going any where.

      I would think the whole t&g Floor was glued. That shouldn't go any where should it?

      Another question: So for the sake of speed, does it matter if the gap is bigger say 3/8  or 1/4"? they still need to fill in the gaps.

      Its a pain in the butt when your "going like hell" to lay a piece down , to find out it is just a little to tight on one edge. then You have to pick it up carry it out cut it again....etc. when you can just make it "a little" loose, to begin with . You just run the risk of it being wider than an 1/8th, some where along the sheet. Does it matter? Will the thinset take care of that?  Its easy to gap factory edges, but your walls aren't always square. It just saves time. is there anything to be said for a maximum gap?

      Where there's A wheel there's a way, got any wheels?

      Edited 5/24/2003 2:19:07 PM ET by MuleSkinner

      1. calvin | May 25, 2003 01:33am | #3

        Muleskinner,

        As a guy that does reno I see it as run it right and leave the gap under the base.  Helps me on the next sheet measurements, makes turns easier, tells me b/4 setting cabs where the goofiness lies, and every floor guy that follows has a smile on his face.  Quicker to just let it lay?  Not if you take the whole thing together.  Then again, I'm just a dumb carpenter. __________________________________________

        Remodeling Contractor just outside the Glass City.

        http://www.quittintime.com/

        1. Snort | May 25, 2003 02:46am | #4

          Even plywood that's out of the weather's gonna move. 1/8" gap is what we are asked to do...but Cal's right, what's the problem with getting the stuff to fit? I'm also guessing your crew doesn't glue, if you're only edge nailing...hmmm. EliphIno!

          1. Edgar76b | May 26, 2003 06:37pm | #5

            No problem at all lolWhere there's A wheel there's a way, got any wheels?

          2. Snort | May 27, 2003 02:55am | #7

            So, what was this thread about?<G> EliphIno!

      2. jimmythetoe | May 26, 2003 09:43pm | #6

        make the tile-setters put their own underlayment down that way when something fails they cant blame it on you.i had a floor guy tell me that the underlayment I put down was excellent hadn't seen anyone do such a good job on it .two years latter when his lino seams failed and the floor bubbled up he tried to say that it was my fault because I put the wrong underlayment down.just another way to pass the buck so we don't have to take responsibility for our own mistakes.

        1. Edgar76b | May 28, 2003 03:00am | #8

          i am An Employee on this one so its not my problem. But That exact same thought occured to me. Who will get the blame.

          I know we are doing it because we are faster, &  cheaper, but I don't know what they do before tile.

          We just nail the perimeter. I was always taught evrey four inches on underlayment .

          Every 6" on sub-floor, which is by the way the 13/16" T & G oriented strand board , made for decking.

           In some rooms it was buckled from aall the rain we had i bet.

          The under layment is CDX which I guess is OK for tile.

          I guess it all has to be spec'ed out by the architect, But i hope they at least nail it better .Where there's A wheel there's a way, got any wheels?

          1. jimmythetoe | May 29, 2003 05:25am | #9

            out here they normally put thinset under the underlayment before they nail it off,at least the good setters do.should carpenters be doing   that ? Sounds like your in the pit!

          2. Edgar76b | May 30, 2003 01:38am | #10

            Yes Sir!Where there's A wheel there's a way, got any wheels?

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