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  1. #1
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    Oct 2014
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    Default Hairlines in grout, one small area

    Early 1950s house, slab on grade. Ground floor tiled bout eight years ago. The one image shows crosswise hairlines in the grout a few feet in, as shown, but they appear absent closer to or further from the slab edge, as in the other picture. No penetrations nearby. Not worried, just curious about likely cause.

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  2. #2
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    Mar 2007
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    Default Re: Hairlines in grout, one small area

    Pics are a bit small, hard to see on my screen.
    But in my area, tile on top of slab always equals cracks somewhere, though mostly I see the cracks running parallel to the tile edge, not perpendicular. Movement is the most common cause.
    Could have been poor workmanship in the grout process also.


  3. #3
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    Mar 2007
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    Fletcher, NC
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    Default Re: Hairlines in grout, one small area

    Photos are a bit small, and lose some detail when zoomed in, especially to 500X, but the cracks in the grout (perpendicular to the grout line) look like shrinkage cracks.

    Is the grout smooth to the touch or rough to the touch (smooth indicates non-sanded grout and rough indicates sanded grout).

    Non-sanded grout used in deep and wide grout joints (greater than 1/16" or so wide by maybe 1/4" to 3/8" deep) used for wall tile in bathrooms and the like does not have much grout to shrink and show shrinkage.

    Non-sanded grout used in grout joints joints wider than 1/8" or so, especially grout joints wider than 1/4" will show shrinkage lines, and the wider the grout joint is, the more shrinkage there will be. Add a wider grout joint with thicker floor tile, and there is a lot more grout to shrink.

    Sanded grout is rarely (if ever) used in 1/8" or less grout joints (especially in 1.16" grout joints) simply because the grains of sand cause issues with being able to force the ground into those narrow grout joints.

    If sanded grout was used in those wider and deeper grout joints, and shows those cracks only in a limited area, my guess would be: a) poorly mixed grout in that section; b) grout/tile replaced and grout poorly mixed.

    Another potential option, but this is typically along with cracks in the tile too, would be loose tile.

    When you tap on the tile in that area, so they all sound 'solid', or does one or more tile sound 'hollow'? Tile sound be fully bonded to the slab, in which case the tile sounds 'solid'. Tile loose from the slab will sound 'hollow'. And partially bonded tile will sound solid where bonded and hollow where not bonded.

    The two methods I used to use for checking tile was: a) a golf ball; b) a wooden stick with a rubber leg cap on it. Method a) was the best as I could show my clients how I dropped the golf ball ("dropped", not "thrown" down) and you can hear the sound, then I would ask if they wanted to do it, and they would all get a great smile on their faces as they went around checking the tile with the golf ball, especially when they found a hollow tile!

    Jerry Peck
    Construction/Litigation/Code Consultant - Retired
    www.AskCodeMan.com

  4. #4
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    Default Re: Hairlines in grout, one small area

    It seems to me that too much water in the grout mixture might also result in that type of cracking.

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  5. #5
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    Default Re: Hairlines in grout, one small area

    Quote Originally Posted by Gunnar Alquist View Post
    It seems to me that too much water in the grout mixture might also result in that type of cracking.
    Correct. Too much water makes the grout weaker, and create more shrinkage as the grout cures/dries.

    I'm thinking that it was possible that they hadn't mixed up enough grout, and they added waterss to what was left in the mixing bucket to make the grout go far enough to complete the job. Thaat would account for those cracks only being in one smaller area, A tlie repair would also create the potential for that, but then there would be a slight mismatch of grout color (old to new) and 'cold joints' where the new grout when in next to existing grout.

    There are several possibilities, we don't have good photos, and we don't have enough information for the details either.

    But we all do speculate at lot here (basically, we have to, even on the inspections because we don't "know" the background history of what we look at).

    Jerry Peck
    Construction/Litigation/Code Consultant - Retired
    www.AskCodeMan.com

  6. #6
    Join Date
    Oct 2014
    Location
    Maryland, DC, and Northern Virginia, electrical only
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    Default Re: Hairlines in grout, one small area

    Thanks, friends.
    I did go and tap the tiles (rubber mallet), and their underpinning appears sound. From the sound.
    Sorry about the photos. I tend to be in a bit of a muddle about how severely to resize photos I'm going to attach. If I did so frequently, I'd sort it out. I've added a tip to indicate size. (Does this make it a selfie?)
    It is, of course, sanded grout. Quarry tile, on a floor? The tile setter would have to have had to be a sheer amateur to try to use unsanded in those spaces. That he was not; he was old, and occasionally a wee bit careless. (I can identify.)

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    Last edited by david shapiro; 01-08-2023 at 02:56 PM. Reason: add image

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