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Thread: Filling expansion joints in concrete floor

  1. #1
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    Filling expansion joints in concrete floor

    My new place has expansion joints that were finished with a 1/2 radius trowel. That is a substantial opening and gets int he way of moving equipment. I was just out laying out the lighting and stepped off the ladder and rolled my ankle. It just about took me down. I’m going out to vacuum and brush the joints clean. What do you suggest for material to put in there to bring it up to grade.

  2. #2
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    You can get a filler at the home center or good lumber yard (or masonry supply) that can be put into the joints with a caulk gun and is self-leveling, but remains elastic. It's typically grey in color. I forget the exact name for it.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #3
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    Locktite PL polyurethane concrete caulk or similar. It is available in self leveling and vertical grade. A backer rod is recommended. It will not support the wheel of a heavy machine or a floor jack. I have filled a few expansion joints with non shrink grout where rolling heavy machinery is common. Grout or mortar is counter-intuitive for expansion joints. It is a bit of a Dilemma.

    Screen Shot 2023-03-03 at 7.18.12 PM.png
    Last edited by Maurice Mcmurry; 03-03-2023 at 8:27 PM.
    Best Regards, Maurice

  4. #4
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    I know some will probably freak out, but if it was mine, I'd fill them with Type N mortar (don't use Type S), and if it cracks all up, then scratch it out (shouldn't be hard to do if it has cracked) and replace it will something softer. I don't know about Northern California, but we don't have trouble with slabs cracking here unless they're really huge.

  5. #5
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    Quote Originally Posted by Tom M King View Post
    I know some will probably freak out, but if it was mine, I'd fill them with Type N mortar (don't use Type S), and if it cracks all up, then scratch it out (shouldn't be hard to do if it has cracked) and replace it will something softer. I don't know about Northern California, but we don't have trouble with slabs cracking here unless they're really huge.
    I have been doing been the same thing with weak homemade grout in driveways where the builder had used 1X4's to divide up the concrete. The wood rots away and folks want the cracks filled. Indoors, I call expiation joints "Control Joints" I have not filled mine in yet, If I do I will use mortar.
    Best Regards, Maurice

  6. #6
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    I don't know that you can even buy ready mix Type N mortar. If it says "high strength", that's probably Type S. To get Type N, you may have to buy the 80 pound bag of plain Type N mortar, and some masonry sand, to mix it yourself. 1 to 4 ratio of mortar to sand should work for this.

  7. #7
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    SIKA make a self leveling caulk that remains flexible. Some of the big box stores carry it.

  8. #8
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    Home Depot has the premixed type N Tom referenced.

    https://www.homedepot.com/p/Quikrete...0260/100318487

  9. #9
    The caulk type fillers shrink a lot and it would take a lot of it, even with backer rod. I did it recently on a carport that I built to prevent debris from building up in the joints.

    I would use high strength repair mortar similar to what Tom M King recommends. 2 or 3x the cost of regular sack mortar, but better result. A pastry-type bag would work well or just a trowel.

    The joints are not actually expansion joints, but shrinkage ones. Concrete shrinks as it cures, and the control joints are to give it places to crack uniformly, rather than randomly. So there is not and issue with filling the joints like there might be with wood.

    https://www.homedepot.com/p/Rapid-Se...188453#overlay

    This particular one I like but it ends up a more tan color so doesn't match concrete gray that well. There are other brands more gray.

  10. #10
    Quote Originally Posted by Paul Mosteller View Post
    SIKA make a self leveling caulk that remains flexible. Some of the big box stores carry it.
    +1 on the Sika

    Fill large gaps with appropriate sized backer rod, use Sika self leveling caulk/sealent and dust over with clean sand, sweep of excess sand when cured.
    I've done this many times and it has held up for years.
    Expansion joints need to be able to move.
    Just my two cents.

  11. #11
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    If you want it non-permanent, use dowel rods (wood or aluminum). I have one place where my planer is and it drove me nuts going across that when I move things into position for longer boards. A 3/8" dowel is almost flush and works fine for me.
    Last edited by Michael Burnside; 03-14-2023 at 4:12 PM.

  12. #12
    Quote Originally Posted by Edward Weber View Post
    +1 on the Sika

    Fill large gaps with appropriate sized backer rod, use Sika self leveling caulk/sealent and dust over with clean sand, sweep of excess sand when cured.
    I've done this many times and it has held up for years.
    Expansion joints need to be able to move.
    Just my two cents.

    You can tell that they are not expansion joints because they are only 3/4" or maybe 1" deep. The 3 or more inches of concrete below is solid.

    An expansion joint, usually at perimeter or transition to other material, will have a strip of fiberboard or foam.

  13. #13
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    True, the sawn recesses used today are there to help tell the slab where it should crack if it wants to. Older slabs, however, may have an actual expansion joint that has a fiber material embedded. The floor in the shop in my old property was like that; poured in the early 1980s in effectively three pieces. Those gaps were "yuge" and would not have been fun with mobile tools.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  14. #14
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    I don’t think these seams can handle a backer rod. They are broad and fairly shallow. I think on the side with shelving I will try a tube of Sika and see how far it goes. I think it could easily become a couple hundred bucks for Sika. If it calc’s out like that I will go with Cameron’s suggestion on the mud.

  15. #15
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    I just used some left over sanded tile grout to fill some control joints and it make a very smooth joint. 15 years later and is is still as solid as when I did the grouting.

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