Is this slab normal?

Discussion in 'Development' started by Perthguy, 2nd Feb, 2017.

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  1. Perthguy

    Perthguy Well-Known Member

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    First build so I have some questions about the slab. I have raised these with the builder but running it past the brains trust in case I get told it's normal and it isn't.

    These are the things I did not expect to see:

    1) a large crack running across the slab from one side to the other and to the ground on both sides.
    2) reinforcing bar visible which appears should be inside the slab
    3) large chunk of slab actually missing near the edge
    4) the edge of the slab looking quite crooked and rough.

    Apologies for the links, I could not get the images to upload:

    slab

    edge

    missing concrete

    crooked edge with rebar visible

    rough edge with rebar visible
     
  2. TerryN

    TerryN Well-Known Member

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  3. Scott No Mates

    Scott No Mates Well-Known Member

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    1) It's how wide???? 1mm. The slab is still very green and hasn't been cured. That's looks like a bit of drying shrinkage. Express your concern as it may permit termite entry but not likely. Are you having polished concrete floors?
    2) They're pegs which were used to hold the forms in place
    3) The brickwork will hide it
    4) the concretor failed 3D geometry, it takes alot of skill to get that shape.
     
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  4. Sonamic

    Sonamic Well-Known Member

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    In a word, no.
     
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  5. vbplease

    vbplease Well-Known Member

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    That concrete mix looks a bit dodgy to me.. I'd expect to see some exposed aggregate. You can request a copy of the concrete mix and compressive strength testing to make sure it complies with the engineer's specs. It shouldn't spall at the edges like that.

    Is the house going to be brick veneer?
     
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  6. WestOz

    WestOz Well-Known Member

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    From the pics, the mix looks like it has A LOT of sand in it, sand is obviously cheaper than cement to = same vol of required concrete.

    If it were me I might take the pics down to the council, ask to see one of the building dept guys, show them the pics, maybe they'll drop by for a closer look.

    Who's doing the build for you @Perthguy ?
     
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  7. Scott No Mates

    Scott No Mates Well-Known Member

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    There won't be any test carried out due to size of the pour ie wasn't required. They may provide the delivery docket to show that the correct compressive strength grade was used.

    The slab was stripped too early/too little care damaging slab edges.

    A well vibrated slab won't show aggregate.
     
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  8. vbplease

    vbplease Well-Known Member

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    At the surface no, but once up to 70mm of concrete has been knocked off there should be some visible aggregate :eek:
     
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  9. vbplease

    vbplease Well-Known Member

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    The strength isn't confirmed unless it's tested.

    http://www.ccaa.com.au/imis_prod/documents/Library Documents/CCAA Technical Publications/CCAA Guides/CCAAGUIDE2007-T53-HousingWEB.pdf
     
    Last edited: 2nd Feb, 2017
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  10. Perthguy

    Perthguy Well-Known Member

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    Double brick.
     
  11. Perthguy

    Perthguy Well-Known Member

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    Thanks guys. I just wanted to know if I should look into this further and wasn't just being first build picky
     
  12. TerryN

    TerryN Well-Known Member

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    It surprised me on my couple of trips over your way how little concrete they used in a raft slab compared to here, even though almost all of your houses are solid (double) brick as opposed to mainly brick veneer here.We have large beams etc, across our slabs that are sometimes 900mm deep.But I suppose we are sitting mainly on clay here and you are on sand.Another thing that surprised me was that the carpenters were still "pitching" the roofs rather than using trusses as they have been doing over here for a long time.The carpenters who I knew said it took a bit of getting used to when they went over there for work,especially the fix-out's,with the houses all been solid brick.Back to the subject Perthguy,the job looks pretty rough, going on the photos,but it's probably not going to effect anything much mate.
     
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  13. Phase2

    Phase2 Well-Known Member

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    Yeah, looks normal enough. As others have said, it looks like a rush job and is a bit rough cosmetically but I can't see that it will affect the house structurally. (provided they've tied the slab together with rebar and mesh) :)

    Your inner bricks sit on the top of the slab and the outers sit on the concrete footing beneath it, you won't see any of the 'defects' once bricks are up.
     
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  14. Perthguy

    Perthguy Well-Known Member

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    I went to speak to Chris the senior building survey at the City. Nice guy. I showed him all my pics and he explained how it works.

    1. The crack is superficial and the slab is reinforced so as far as he knows it won't be an issue. I checked the rebar before the slab pour and it looked correct to me.

    2. The external leaf of brickwork will go on the footings and the internal leaf will go on the slab. Any minor issues with the edge will be taken up with the brickwork.

    3. The rebar in the footing is a pin that the grano workers use for a level. It should have been removed but can be ground off at this stage.

    He has seen a lot more slabs than me and thought this was fairly typical.

    Thanks for the advice
     
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  15. Perthguy

    Perthguy Well-Known Member

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    Exactly what the senior building surveyor said! :)

    I checked the mesh before the slab pour and it looked right to me. The mesh had good coverage, the moisture barrier was in place and they used spacers to hold the mesh away from the moisture barrier. That's good! I have seen the mesh dumped on the moisture barrier before, which is not good.
     
  16. norwoodman

    norwoodman Well-Known Member

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    The crack running across the top surface isn't anything to be concerned about, as this looks like a shrinkage crack resulting from the curing process of the concrete (concrete loses water and gains its design strength over a period of approximately 4 weeks).

    The edge finish, however, looks quite poor and probably is a result of the formwork not being greased and removed appropriately.

    If this is meant to be a brick veneer house, I would expect to see rebates at the slab perimeter, which I am not seeing.
     
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  17. wombat777

    wombat777 Well-Known Member

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    They will need concrete evidence :p
     
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  18. vbplease

    vbplease Well-Known Member

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    It looks like the rebate for the outer brick leaf is covered in sand?

    I was thinking the dodgy concrete edge might be a problem for the brickwork..

    You should see the vapour barrier terminate up the side of the concrete edge. It prevents slab edge dampness for clayey sites (outside of WA) I've heard some get away with not putting in the vapour barrier at all in WA due to the sandy sites being self draining..
     
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  19. Perthguy

    Perthguy Well-Known Member

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    It is now because there is a lot of activity on site. I checked the rebate before the slab was poured and it looked good to me.

    Me too. I have bricked and I would not like to try an line up a wall on that slab. They better have good brickies then! I will check when the first courses are down and make sure they are straight.

    I'm not sure what happened to the vapour barrier. I checked before the slab pour and the barrier was definitely in place. Could they have cut it when they took away the formwork?
     
  20. Perthguy

    Perthguy Well-Known Member

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    Double brick.
     

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