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I'm having a house built and they just completed pouring the slab for the foundation a few days ago. When I inspected it today I noticed several narrow (but sometimes long; one or two do them appear to run nearly across the entire slab) cracks in the concrete. Here are some pictures:

Crack from corner of shower recess Long crack running from opposite corner of the same shower recess Continuation of above crack

Can anyone tell me if this is something I should be concerned about, or is it standard to find these kinds of small cracks in freshly laid concrete?

Secondary question; I also noticed a few other things that seemed like defects. Are any of these cause for concern:

Missing chunks of concrete: Missing a small chunk of concrete Another missing chunk of concrete

Fastener not secured to anything: Fastener is not actually secured to anything (concrete beneath it is missing)

Footprints in shower recess concrete: Footprints in shower recess concrete

Edit - Here's a shot of what was in place immediately before the slab went down:

enter image description here

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Looks like a rather sloppy pour. –  DA01 Sep 8 '12 at 7:09
    
Are there expansion joints in the slab? Also there's no lagging around the pipe where it penetrates the slab bad form! Did they used steel riobar? Did they use rio chairs to hold the steel at the correct depth in the concrete? –  UNECS Sep 8 '12 at 10:58
    
@UNECS - Negative on the expansion joints. They did use steel riobar, yes. And I'm not positive but I believe they did use chairs to hold the steel in place. What they did was before pouring the actual slab they excavated a network of trenches and filled that with concrete, and then had steel bars protruding vertically out from that at regular intervals (I'll add a picture of this). My assumption is that they used those vertical bars to secure the riobar in place, though I wasn't onsite at the time to see if that's what they actually did. –  aroth Sep 8 '12 at 12:22
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@DA01 - Sloppy as in "ugly but still functional", or sloppy to the point where the structural integrity has been compromised? –  aroth Sep 8 '12 at 12:32
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I agree that the pour looks bad, but to answer your title question: it depends. Cracking in concrete surfaces can be perfectly normal depending on the type of concrete and climate. Here in Northern Nevada, for example we have two types of concrete: concrete that is cracked, and concrete that is going to crack. –  Matthew Sep 11 '12 at 16:50

2 Answers 2

Concrete will crack naturally on its own unless it is given a place to crack such as control joint or expansion joint. As the concrete is curing it is heating up and expanding. In the summer time, I have seen the slab crack before being able to walk on it.

Regarding footprints, it is tacky. However, the roughness can actually help the concrete and thinset to bind unless it is flaking.

One criticism......the young lady wearing the flip flops should not be walking around a construction site. Stepping on nails, rusty re-bar, broken glass etc is a distinct possibility. Safety first!

As suggested by another responder, if you feel excessive water has been used then a core sample can be done and a test break can ascertain whether the concrete is no good.

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A blind person could of poured better than that! Looks like the pour had too much water in the mix. When too much water is added, the aggregate sinks to the bottom and weakens the final product

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