Cracks In New Concrete

Discussion in 'Buildings & Infrastructure' started by Timmer, Jul 16, 2017.

  1. Timmer

    Timmer Member

    This year we had an extremely reputable builder construct a new steel framed building, the whole project has been perfect except the concrete apron. We have cracks right across in 8 places, although these have been cut and filled with mastic it looks very untidy and several people have said we should not accept it. Builder says it's because of the hot weather and that concrete will crack no matter what precautions but I now look at every piece of concrete I walk over wherever I go and have not seen anything like this. Any advise would be much appreciated, the last thing we would want to do is fall out with the builder but at the same time this is probably the worst bit of concrete on the farm and he so far doesn't seem that interested. Can these cracks be cut out and re- concreted?
  2. simmy_bull

    simmy_bull Member

    North Yorkshire
    Did he take any precautions such as covering it etc to help with the hot weather?
  3. Steevo

    Steevo Member

    Small cracks or larger ones?
  4. Lazy Eric

    Lazy Eric Member

    Are they just surface cracks ? If so be ok.
  5. multi power

    multi power Member

    How big is the apron? Any expansion strips?
  6. ARW

    ARW Member

    As said are they just surface cracks or actual cracks that will make it turn to crazy paving. Maybe worth contacting the concrete company an analysing the sample
  7. 2 things are guaranteed with concrete
    it will cure and it will crack, now obviously you can try to stop the random cracking by laying on visqueen instead of straight onto hardcore, wetting the concrete immediately after it's cured, spraying a sealer on, putting in movement cuts or laying the floor in much smaller slabs, once you have a got a random crack it shouldn't grow in size much but will look unsightly
  8. Forever Fendt

    Forever Fendt Member

    Plastic shrinkage cracks appear very quickly ,should be no deeper than 3mm not nice to look at but sometimes unavoidable the surface has dried out quicker than the concrete lower down in the slab, Poly fibres in the mix helps reduce this and a blended cement would help ,warm days with a bit of breeze are the worst it can happen on indoor slabs to if there is a doorway allowing a breeze to blow over the slab but these are not seen as power floating will rub some fat from the top into the cracks, best thing to do is finish the concrete and pull some dpm over it a water this to slow the hydration process down and it could be sprayed with a sealer as soon as the concrete is finished
  9. Forever Fendt

    Forever Fendt Member

    its more to do with the choice of mix used and not a quality issue
  10. Forever Fendt

    Forever Fendt Member

    Just re read the op post it does not sound like the above although this is a common problem if it had mesh in it correctly placed and had been saw cut correctly and timely this should not happen as @RWG Contracts has said, if they are random shrinkage cracks i think i would be telling them to sort it and not accept sealant filling as a repair
  11. Turra farmer

    Turra farmer Member

    The concrete should have expansion joints cut every 6m in both directions , 25mm minimum into the slab to allow controlled cracking ,
    Sometimes even with that , if there is a strong sun and a shadow you might get cracking up the shadow line , if the concrete has mesh init I don't think it's much of a problem if it's only small cracks ,
    Dyffryn likes this.
  12. Clive

    Clive Staff Member

    How many expansion joints did they cut and how soon ?

    Last floor we had done they cut the joints as soon as they finished floating it making 6m squares

    No cracks at all as a result
  13. Timmer

    Timmer Member

    From what I can see at the edge, the cracks are very thin but do seem to go down to the bottom. Cutting them out and sealing them has made them stand out more but it was thought this would be better than letting water get down into it. The entire apron is 11m wide by approximately 35m long. It was laid in 2 halves with expansion joint in between and 1 across each length. It has metal reinforcing and was sealed afterwards but no sheet. Mix was rc40 no fibres. Can we cut these cracks out in perhaps 1m wide strips and re concrete with expansion joints each side? It would still look better than what we have now!
  14. Forever Fendt

    Forever Fendt Member

    slabs way to big i am afraid,no going back from here max size here 4.572 x6m and no cracks
    Sussex Martin and multi power like this.
  15. Interesting. @RWG Contracts what's the sealant you talk off?

    Laying a c40 pad between 5-7 inches with mesh on Thursday, 5 x 25 m. Planing on cutting it 3 times and filling with mastic - that ok?
  16. Forever Fendt

    Forever Fendt Member

    max distance 36 x thickness and not more than 1.5 times the width,if you know where your cuts are going to be consider cutting every other one of the bars out of the mesh under the saw cut and make sure the strands do not cross the cut joint
  17. I spray a sealant on the top to help concrete cure, stops dust rising etc etc, what's slab for?
  18. Farm / tenant yard. Also outside biomass boiler so will get a bit of use
  19. Timmer

    Timmer Member

    So could I cut out these cracks in strips and re-concrete? Bit miffed with the builder, can't help feeling I'm being fobbed off. Keeps basically saying he did everything and it will still crack just one of those things. He does a lot for some really big set ups and I can't imagine they would be ok with this
  20. Morph

    Morph Member

    photos ?

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