Pool Deck - Tamped concrete

Hamilton, USA

We've just had a pool installation completed which included a stamped concrete deck and patio surrounding the pool. We chose a pattern known as ashler slate. There are a number of what I would call surface defects in the concrete. Mostly on the edge of the individual slates there are spots in which the concrete is not smooth. It appears grainy and slightly depressed below the finished surface. I asked the mason if the forms were kept clean as I thought the problem might have been caused by concrete on the form pushing into the surface. The mason said no. It is caused by tension on the surface of the concrete when they tamp down on it. He indicates this is normal for stamped concrete and won't affect the integrity of the concrete. I don't know much about concrete, and I also don't want to be unreasonable, but his explanation sounds a little too convenient. I would appreciate any advice you could give. 

Thank You, C.L.
Charles,

It is not easy to visualize the problem from your description, so do not expect too much from my answer.

It is not clear to me what size and depth are these depressions. Does it look like something broke off (spalled) or what you see is the surface as left by the mason?

His explanation does not make much scientific sense, but that may be because he does not know the correct terms. It sounds to me like some concrete stuck to the forms when they lifted them. The stress he is referring to may be the stress when the 'skin' of the concrete stretches and breaks. This would leave a rough surface inside a depression.

I tend to agree that there is no danger to the integrity. If the concrete is over 14 days old you should take a pocket knife or sharp screw driver and try to scratch the surface of the concrete (do not push hard). It is OK to see a lighter color scratch, but no material should come off. Surface dusting is a sign of finishing problem.

Is the concrete colored? If yes, is there a difference in color inside the depression?

Is that a visual problem? Seems to me that a slight irregularity will fit ok within the stamped texture (whatever ashler slate is...).

If you need more to make you feel secure go look at some of his other stamped concrete (you did that before you hired him, right?). If this is a common thing then you may accept the explanation and enjoy the pool...