Cracks in new concrete

10 years ago

I just had 1400 sq feet of concrete patio done last month, with color concrete, stamped. The contractor did the work on a very hot day, and then when I asked him if I should spray water on the concrete, he said no.

We had 105+ days for a week right after that, and looks like the concrete has not cured well. Right away nearly half of the controlled joints had long cracks, and cracks started appearing (and getting longer) on the concrete surface (see the pictures).

It also seems like the top layer of the concrete is not very strong, as I dropped a screwdriver from 3 feet height and it chipped the concrete.

The contractor says this is normal (no surprise there :-)). Is that correct? He says he will put a quick patching, and once the concrete is sealed, the cracks won't be visible at all.

What do you guys think? Thanks for your advice.

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Comments (4)

TxMarti
10 years ago
I think your concrete guy is wrong, or telling you this just so he can get out of his responsibility. When we had a slab poured in July, the contractor told us to keep a sprinkler on it moving it around every so often. I can't remember how long, 24 hours I think.

I don't think a patched crack will ever be unnoticeable.

I'd have another contractor take a look at it. If you have to take the first contractor to court to pay for this, you may have to hire an expert.

This post was edited by marti8a on Thu, Aug 29, 13 at 21:55
StoneTech
10 years ago
I agree. Totally unacceptable.
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StoneTech
10 years ago
I agree. Totally unacceptable.
GardenWeb9
Original Author
10 years ago
Thanks for all the feedback!

I called the ready-mix concrete company my contractor had used, and inquired about what exactly was ordered by my contractor. It turns out that he ordered the concrete with a slump of 5, which is marginal at best (4 or less is desirable). So the concrete was already somewhat watery. On top of that, he added 40 gallons of water on arrival (to 16 cubic yards of concrete), making the slump to 7.5 - WAY too watery. The water to cement ratio was 0.59, making both the ratio as well as the slump too high to make acceptable concrete.

It turns out that he clearly violated the ASTM C 94 standard. According to the ready-mix quality control guy, he should have requested plasticizer instead of adding so much extra water. Plasticizers are cheap ($1-3 per cubic yard), so it is really surprising that he cut corners there.

Now I also understand why he asked me not to spray water, as he know he already had put in too much water to begin with. So we ended up with too much water during pouring, and too less water during curing.

Just to gather some conclusive evidence, I have asked the concrete quality control guy to come by tomorrow and do some Schmidt hammer testing, so that I can clearly show that the slab is weak. (For those who do not know this, the test is free, and non-destructive).

Then the fun will begin when I break this to the contractor...