Garage floor cracks

Discussion in 'Repairs & Maintenance' started by Emboon, 9th Jun, 2020.

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  1. Emboon

    Emboon Well-Known Member

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    There are some cracks on the edge of my garage. The cracks seem pretty straight and the garage floor is higher than the external concrete.

    Not sure about the history of the house but is it possible the garage concrete was laid first before the external patio thats why the crack is very straight?

    Or can this be foundation issues due to movement? Should I worry?

    Pictures below.

    Cracks

    I am not very knowledgeable with it and I am hoping for your patience and understanding.
     
    Last edited: 9th Jun, 2020
  2. Lindsay_W

    Lindsay_W Well-Known Member

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    That looks like an intentional gap not a crack, possibly due to pouring one first then the other. Nothing to be concerned about in my opinion.
     
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  3. vbplease

    vbplease Well-Known Member

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    they should be poured separately.. I’d be concerned if they were poured together..

    The garage, which likely consists of a raft slab with the rest of the house should be constructed on firm natural ground, while the patio slab doesn’t get the same ground preparation and could even be on fill material.. so it’s inevitable there will be some differential movement unless they’re dowelled together.

    I wouldn’t be concerned.. you could fill the gap with some mastic sealant if you don’t like the look of it. If the patio slab really starts to move you may need an engineer to look into it
     
  4. Emboon

    Emboon Well-Known Member

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    Thanks to the quick response.

    The reason I thought it was poured together was this side of the wall so I assume they were connected and leveled before.

    IMG-20200609-152503

    Right now the garage floor is higher by about 1cm.

    How can I tell that the patio slab movement is unacceptable or not? Whats the best way to tell
     
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  5. Mark F

    Mark F Well-Known Member

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    It looks like the joint should be an expansion joint. Is there anything like a dense foam in the crack or can you see down 5-10 cms? It is likely that the rh side slab (garage?)is poured on top of the house foundations while the lh side (patio?) has been poured on compacted earth or gravel/sand which is prone to further compaction/shrinkage. This would explain the slight drop but it doesn't seem to be something I would worry about. I would only check further if the crack was widening rather than a little vertical movement.
     
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  6. Antoni0

    Antoni0 Well-Known Member

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    Long periods of dry weather can cause it depending on the sub-soil, it's quite common in SE Qld as there is a lot of clay around.
     
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  7. Propertunity

    Propertunity Well-Known Member

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    Its an intentional expansion joint. Soils expand and contract with moisture content - rain / drought / big trees nearby sucking up water and so on. Not really a concern and designed to stop cracks developing.
     
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  8. Scott No Mates

    Scott No Mates Well-Known Member

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    It's a sawn expansion joint.

    It is higher to limit the entry of wind blown rain into the garage.
     
  9. Antoni0

    Antoni0 Well-Known Member

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    Yeah, the saw marks are meant to be there but the slab is twisting, you can see it from the different heights which suggests something funky is going on beneath the ground
     
  10. Emboon

    Emboon Well-Known Member

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    Could you expand on what you mean the slab is twisting?
     
  11. Antoni0

    Antoni0 Well-Known Member

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    In the photo below it shows what looks to be uneven levels.

    Probably nothing to worry about as long as it's not your house that starts to crack or shift but house slabs do move over time too. It might cause a trip hazard, where you might want to fill it or grind it back. No harm in keeping an eye on it and calling in professionals to look at it if it gets a lot of worse.


    drop.PNG
     
  12. Scott No Mates

    Scott No Mates Well-Known Member

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    Looking at the last photo, it would appear to be a tooled joint on the edge of the garage slab and a float finish on the outside slab (green).

    There appears to be some slight difference (out of parallel) in the joint. @Emboon - have you got a wider photo of the area of concern?
     
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  13. Emboon

    Emboon Well-Known Member

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    Yup its uneven levels. The garage side is higher by about 1cm. Thanks for the tip.
     
  14. Emboon

    Emboon Well-Known Member

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    Did you mean photo that captures the full length?

    This one is about 80-90% of the area of concern.
    IMG-20200609-134303


    Here's another wider shot

    IMG-20200609-184358
     
    Last edited: 9th Jun, 2020
  15. Antoni0

    Antoni0 Well-Known Member

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    Sometimes they can put a small step in between the two slabs to stop dirt, leaves or water blowing into the home, it's a bit hard to see in those pics.
     
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  16. Emboon

    Emboon Well-Known Member

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    Yeah I tried my best to show how uneven it is. Do you know what thats called, The small step? Is that something I can install myself perhaps?
     
  17. vbplease

    vbplease Well-Known Member

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    Definitely poured separately.. it's not a saw cut joint, not an expansion joint, nor an isolation joint (typically contains compressible foam - ableflex)..

    it's a cold joint, where the garage slab was poured first and the patio slab poured hard up against it.. looking at the two slabs new the wall you can see the outline of the large rocks cast into the garage slab, formed into the patio slab where it has pulled away from ongoing ground movement.

    Unfortunately there won't be any reinforcement connecting the two slabs, so you'll be at the mercy of the weather, vegetation etc for ongoing movement.

    I'd install mastic sealant in the separation to prevent surface water entering, thus reducing further movement. Also a transition ramp similar to prevent a trip hazard.. if the movement gets too bad you'll have to rip the patio slab out. When putting a new slab in, make sure you dowel into the garage slab and work on drainage, vegetation causing the ground movement.
     
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  18. Antoni0

    Antoni0 Well-Known Member

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    It's cheaper to use the mastic sealant like vbplease said to fill the gap up but you can use products such as these to stop water and leaves rolling in along the ground.

    Weather Stop Garage Door Floor Seal Kit 20mm (High)
     
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  19. Emboon

    Emboon Well-Known Member

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    Sorry, I didn't quite get this part. Which outline of large rocks were you pointing out?
     
  20. Joynz

    Joynz Well-Known Member

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    Looks a bit like what happened when a new driveway was laid at my mother’s house.

    There ended up being a lip on one side of the driveway where it meets the footpath.

    They had poured the driveway correctly, but the old footpath was uneven so it looked like the driveway was laid wrong even though it wasn’t.