Hi, Just completed the pour of a garage foundation and notice there are hairline cracks in the slab. The foundation was pour with 6 sack pea gravel and #4 rebar with a 4" slab. Contractor said it was the way the concrete is dried - too quick... He said he will fix it. Should I be concerned for a new slab has cracks? Or this is common? The slab did exposed under the sun while drying. Thanks in advance,

All concrete slabs crack. Actually, all concrete anything cracks; walls, roads, piers, floors, etc... I would not worry too much about a hairline crack. I am surprised the contractos is offering to fix this but would like to know his proposal. Expansion joints and proper drying conditions would make less cracks initially but eventually they crack.

Yes, They all crack! I saw a contractor place long thin wires in the top surface 1/4 inch into the wet concrete, When I asked? He stated they would give you nice straight controlled
Cracks instead of crooked ones. He was right!

We are building a new home and the foundation was poured the other day and there is a continuous hairline crack from the bottom of the foundation across the slab to the other side of the foundation (to the bottom of the slab). Basically one continuous crack. I know some say not worry about hairline cracks in cement but this goes all the way across and down the sides of the slab. Should I be concerned.

The builder not the concrete guy said there is nothing to worry about it, ours is not so bad. Anyway, to fix, we just bought the concrete crack fix from Home Depot and paint over the concrete inside the garage. Yes, they are still there but no so noticeable. Hope this helps.

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Originally Posted by dtexas

we are building a new home and the foundation was poured the other day and there is a continuous hairline crack from the bottom of the foundation across the slab to the other side of the foundation (to the bottom of the slab). Basically one continuous crack. I know some say not worry about hairline cracks in cement but this goes all the way across and down the sides of the slab. Should I be concerned.

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This question probably should have been asked in a new thread,I just happened across it.

And,NO,you shouldn't worry much about the crack,if there is rebar or wire mesh below grade the slab will stay together.

Also think about the land the slab was placed,was it new soil,backfill,an old landfill... etc,some settling may occur(just like on the cereal boxes)as long as it doesn't tear some sub level pipework or other utilities,don't fret it,It's Very common.

Hope this helps,

Ken

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Originally Posted by yip88

Hi, Just completed the pour of a garage foundation and notice there are hairline cracks in the slab. The foundation was pour with 6 sack pea gravel and #4 rebar with a 4" slab. Contractor said it was the way the concrete is dried - too quick...He said he will fix it. Should I be concerned for a new slab has cracks? Or this is common? The slab did exposed under the sun while drying. Thanks in advance,

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All slabs crack to some degree. Especially, those slabs the were not properly cured. A lot of slabs have temperature cracks - where the slab does not cool evenly from the middle out to the surfaces (top and bottom). Air entrainment can help. I recommend placing a blanket over the slab after the surface has hardens a little. Also, slab uniform thickness has a great part in how the concrete cures.. If it is not an even thickness, then concrete will crack at its weakest point - usually at the thinnest point. Which is why a slab with control joints placed properly through out the slab, will crack outside the control joints if the thickness is thinner elsewhere.

As everyone else has stated above hair line cracks do not effect the slab structurally, it is just a barely visible drying/shrinkage crack. On most slabs we brush in dry cement powder and spray with curing agent to seal but most are barely visible and only noticed if really looking for them. Big cracks due to poor workmanship need to be addressed as if you wish to tile or similar over the floor these can cause cracking in the grout etc.