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Garage slab cracklines

Discussion in 'Repairs & Maintenance' started by Wukong, 26th Jan, 2016.

  1. Wukong

    Wukong Well-Known Member

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    Noticed these cracks in the garage recently. Reckon they would be part of the main house slab.

    One long crack that is ~3.5meters long.

    Big concern? i.e. defective slab or something that can be easily fixed.
     

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  2. Hanison

    Hanison Well-Known Member

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    2 notable things about concrete.

    1. It can never be patched and made to look the same. Using concrete to patch concrete will always result in a discoloration. Not sure about the science of it but its a real world fact.

    2. Concrete will always crack. Even expansion joints at every 3 meters on reactive soils will still crack. Soil expands and contracts with moisture content. Its an inevitable problem unfortunately.

    Having said that.
    I love concrete.
    I plan to build a house out of concrete some day.
    But you cannot expect perfection from an imperfect product.

    If your still really concerned. Get a contractor out to take a look at it.
    They will be able to tell you within 30 secs if you have something to worry about.
     
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  3. WestOz

    WestOz Well-Known Member

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    Whilst poured at the same time (many trucks, mixes can vary) they are usually two separate slabs.
    Depending on specs the House slab could be thicker than the garage floor.
    The house slab likely has rio mesh running through it, not usually done for a garage (or drive/path) due to cost, material & labour.

    Mix ratio plays a big part as well as weather during pour and cure (shrinkage), i.e. if its a hot day the truck driver may be asked to add more water to the mix before pouring so it slows the cure process giving the boys extra time to work it.
    You can read more about it here - Why Concrete Cracks - The Concrete Network.

    Nothing to be overly concerned about, if you want to cover it up and make the garage tidier, stop oil stains etc, there's lots of options - garage floor - Google Search
     
  4. Scott No Mates

    Scott No Mates Well-Known Member

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    It's a crack. Don't step on it or you'll fall all the way to Hades.

    No need to patch, it's not a fault just a weak point in the slab (could well be the place where the reo was discontinuous & meant to crack/shrink)?
     
  5. hematite

    hematite Well-Known Member

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    Garage slab is usually different to the house slab.
     
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  6. Propertunity

    Propertunity Exclusive Real Estate Buyers Agent Business Member

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    Unless the crack/s are 4-5mm wide, they are considered cosmetic only and not structural.
     
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  7. monalisa

    monalisa Well-Known Member Premium Member

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    Hi @Wukong

    These are probably settlement cracks. I understand these may be linked to the type of soil.

    I think clay soils are more prone to it.
     
  8. Paul@PFI

    Paul@PFI Tax Accounting + SMSF Business Member

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    Very common in our climate. Your building warranty will define a crack based on its thickness not its length. If you cant put a object like your pinkie in the crack its not a crack. Hairline stuff is very normal. One treatment to hide it is to clear the garage then waterjet it absolutely clean. Even then it wont be clean. ie oil paint fuel etc drips. Paint with a membrane sealer like in carparks. Its a concrete colour and REALLY STINKS.

    Only now you have to put up with the squeally noise when you turn car wheels.
     
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  9. melbournian

    melbournian Well-Known Member

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    this are normal comestic cracks. it has to be with the weather at the time it was poured, the curing of the slab, moisture levels, soil type and how long did you wait before the frames were put in. Unless a 20 cents coin can go in, it is fine. Also if it was raft slab, waffle slab all makes the difference

    Also - not sure abt garage slabs being different - as they're all poured at the same time and using the same steel mesh. Unless it is the driveway.
     
  10. norwoodman

    norwoodman Well-Known Member

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    Those are shrinkage cracks rather than anything major - the result of changes within the concrete itself due to the curing process. Concrete loses water during curing, which results in some internal tensile stresses in the concrete which causes cracks due to concrete being weak in tension.

    As structural engineers we often detail sawcuts in slabs deliberately to control the most likely location of cracking - still no guarantee though. Width of the crack is also a good indicator of crack depth, and if it is hairline in width it won't be deep at all. Pretty common in slabs and nothing to be concerned about.
     
  11. Jony Wen

    Jony Wen New Member

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    It looks like it is less than 2mm or even less than 1mm.

    It is considered normal cracks.