Hello.
I had the walk to my front door and steps redone in early Sept. The old flagstones were removed, cement cleaned up, and new cement was poured over the old concrete base, in which a mixture of the old and new flagstones were reset. The walk is 3ft wide, sitting on the ground. The last few days, the temperature dropped below 40 F for the first time since the walk was redone -- I live in New Jersey. The cement showing between the flagstones is now full of fine hairline cracks in a spiderweb pattern.

Is this normal? Do cracks like that always happen? If not, what may have caused this to happen?

I am concerned that rain water will fall inside the cement cracks and cause the cracks to open up more when it freezes. I don't want that to happen. Part of the reason for redoing the walk and steps was to prevent water from seeping into the basement through cracks/opening in the walk. The walk/ground slopes toward the house, and I get a lot of rainwater runoff coming down the walk. What can I do to prevent the cracks from getting wider? Should I have the walk redone?

Thank you in advance for any information you can give me.

 

Unfortunately. concrete cracks.

Am told if it reaches 1/4" of separation, there was an error or event that should not have happened.

I would guess the majority of concrete walks, drives, etc. will crack. You shouldn't have a problem if the job was done well.

Major cracks will depend on the soil prep, min of 4" thickness, use of rebar or steel grid and proper placement of the steel in the pour. If it was cold (40 deg or lower) when poured and they used calcium additive with steel mesh, some of it could have disintegrated. If it reached that cold during the first 3 days after the pour, it is also not ideal. If steel reenforcement wasn't used, then fibercrete should have been.

Talked to more than a few concrete pros who have told me, nothing one can do about eliminating cracks.

Most cracks won't go all the way through the slab so rain water freezing shouldn't be a concern.

Hope your concern isn't really a problem and time will show all is well.

 

Thanks for the reply. I don't believe any steel was used under the cement and flagstones. There was just some concrete. Total thickness of at least 4 inches. The temperature in the first few days was not an issue. It was warm for 6 six weeks after it was done, which was 7 weeks ago.

Is it possible that the cement was not mixed properly? Like too much water was added when mixing it. Or could it be that it did not cure properly because successive layers were applied after waiting too long and the previous layer got too dry?

 

The spiderweb cracks between stones set into concrete would be completely normal. This is because the stones should not have been set into concrete. They should have been laid atop the concrete in a mortar bed. Any concrete shrinks a bit as it hydrates. It can't shrink around something rigid like a stone, or a re-entrant corner (a corner pointing into a slab) so it has to crack around it.
Also, when concrete cracks, it cracks all the way through the slab, not just on the surface as some people suggest. The only cracks that are strictly on the surface are crazing types of cracks caused by the surface drying out too quickly. I would assume that yours are shrinkage cracks caused by pouring concrete around a static object. It may have been compounded by pouring too wet, because wetter concrete shrinks more, but it would have cracked no matter what.
As to the rainwater getting through the entire thickness of the walk, I doubt it. You said the new concrete containing the flagstones was poured over the old concrete base. The rainwater may seep through the new stuff, but will stop when it hits the original concrete layer. However if it freezes and expands there, it can pop the new layer loose from the old.

Pecos

 

You said the flagstones should have been placed on top of concrete in a bed of 'mortar'. That was what they did, except I thought it was a bed of cement. How is cement different from 'mortar'? What is the difference between concrete and cement?

How can I prevent the hairline cracks from opening more due to water freezing? Is there a way to seal them?

Thanks!