New concrete patio has hairline cracks throughout-what are my options?

Tina1112

We recently had a new patio put in my backyard. About 2 to 3 days later hairline cracks started appearing some running from the front of the area to the back. When I mentioned it to my contractor he said that on his second trip to finish the job he also noticed the cracks. Since he is the landscaper for my backyard project he consulted with his concrete person and was told that he was probably given a "hot load of concrete", and that the concrete stayed in the mixer too long. My contractor is willing to do whatever needed to fix the job. But my question is what are my options? We were going to put flagstone over the concrete at a later point, so the contractor suggested that we could get it done sooner and he would give us a better price to have it done now, rather than next year. He is also willing to take up the whole thing if need be. I don't really want to go through putting a whole batch of concrete down again, but I also don't want the cracked concrete under the flagstone to haunt me later down the road. Is it okay to put the flagstone over the concrete or should we go with doing it over again?

jomama45

The concrete guy should know, without a doubt, if it was a "hot load". For someone who does it for a living, there's not much "grey area" in this part of it.

I'd let it sit at least a month, longer would be better, to ensure that it's done shrinking before installing a wet-set flagstone over the top of it. If it's going to fail structurally, it's best to let it sit through a winter (assuming you're in a cold climate that sees freezing) to put it to the test.

W/o seeing the patio, it's relatively hard to troubleshoot though.......

Canarywood1

I agree with jomama45,if it was a "hot load" he should have known and rejected it,although there are other reasons for hairline cracks to appear,soil compaction and weather being two of many.

by the sun which causes faster evaporation of the concrete water contents. The rapid drying of concrete causes the concrete composition to contract early in the curing process, causing hairline cracks. Additionally. this concrete dries quicker on the surface than at the core. The differences in drying and expansion and contraction will almost always yield hairline cracks.

Tina1112

Thanks JoMama and CanaryWood for responding.

Mort

This normally happens when a contractor tries to do two things. The first is order the concrete with a lot of accelerator so he isn't there all day, and the second is add a lot of water so it's easier to work with. I can't say this is what happened for sure, but I'm guessing it was. All the water he probably added will increase the shrinkage, thereby causing the spider cracks.