I have about 10 cracks in my concrete so far. All concrete will crack.

1. How deep did they pour it?
2. What did they use to reinforce it, rebar or chicken wire?
3. What kind of base rock did they use. Did they pack it in and water it first?
4. Did they put control joints down?

90 degrees for a concrete pour isn't a big deal. It's not optimal, but it's within tolerable temp's.

I was going to ask the same questions as Barco and am especially interested in #4. Did they install expansion and/ or control joints and if so, at what spacing?

Also, are all the cracks hairline or is there separation? Pics might help.

Ripping out and re-pouring concrete is no big deal, but if you're getting cracks because of problems from Barco's list then you want to make sure they fix it before re-pouring.

thanks for the replies...I think the preparation & setup was right on: 4-6" slab, rebar, they saw-cut control joints.

the cracks are "hairline" cracks that formed prior to cutting the control joints (which they did about 24 hrs after pouring) which leads me to believe the concrete cured too quickly (which concerns me that in the long-term, could it worse?)

Yeh, when I contracted my concrete from a moron, I told him we need control joints, we even agreed exactly where each joint was going to go. Well, at the end, I asked him where the joints were and his eyes rolled in the back of his head because he never made them. Then he started going into how you can saw cut them after the fact.

Once you are to the point of saw cutting control joints in, you are pretty much SOL IMHO. I never bothered cutting them in....because many cracks in the concrete are formed right away like in the first 24-48 hours while the concrete is green ....you just can't see them yet. They just get worse and worse with time as the concrete contracts and expands. So when you saw cut them later...all you are doing is putting more cracks down adding to the ones you can't see yet. You need to put the control joints down when the concrete is wet using a jointing trowel so you will encourage the concrete to break on that line straight "WHILE its CURING". You may not see the crack for 1-3 months but it was most likely created in the first 24 hours when the concrete was partially dry enough to be rigid but "very weak" and crumbly.

Concrete is not plaster, 90 degrees should not be a problem. The only temperature problem with concrete really is "freezing".

They poured sidewalks out here "all day" in the 90 degrees awhile ago for a building expansion and theres no cracking at all. You just need professionals doing them that have laid 1000's of sidewalks. You think when they are building a road, bridge or elevated road here in Texas, they stop pouring concrete when its over 90 degrees. They would never get done started. Go check their work....Not a single crack.

I'm sorry, but you like me, have people that don't know what they are doing working on your concrete and for me, I should know better and still got fleeced.

We are going to top our concrete with a KoolDeck toping and may go with a pattern to disguise the cracks. Thats always an option if you just get tired of fighting.

The thing about pouring concrete in high temps is the concrete gets HOT when it's curing. If it's hot outside, it actually makes the concrete cure a lot quicker (and get that much hotter). The quicker it cures, the more likely it is to develop those stress cracks. There are admixtures that can be added to the concrete that retard the cure time, they also keep the concrete cooler during curing. In our commercial work the GC's usually call for retarders AND they start pouring at 3 or 4 in the morning to take advantage of the cooler nighttime temps. By the time the sun comes up the concrete has already set up.

Sawcutting control joints is acceptable practice as long as the concrete isn't allowed to cure out too quickly. I know they still hand tool joints in residential construction, but you never see it in commercial construction anymore.

I've watched them build a big piece of the Austin toll way here outside of my office...all through the heat of summer, all concrete, no cracks.

In my office building complex, I watched them pour sidewalks and concrete curbs with the temperature about 101 and there are no cracks there either. They work fast enough they don't need any retardants. I don't know how they do it at 101 degrees except they wear bandanas inside of their helmets. Its still relatively green stuff...but I don't expect to see a single crack.

All of this is commercial construction...all of them have hand tooled expansion joints.

Using a diamond blade to concrete concrete is a lot more expensive and a lot more time consuming. It takes about 2 minutes to run a jointer. In the case of our sidewalks they have felt expansion joints.

Once rebar reinforced 5-6" concrete is completely dry, you can take a sledge hammer to it and its unlikely to crack with a single blow.

The only case I believe heat could be a factor is "overworking" the concrete and so thus the surface is essentially dry and you are trying to force it to do something that you are past the time to try and do....but thats more of a problem of insufficient work force to do the work than actually the heat in my opinion.

Funny thing...I went to lunch and my car was parked in a parking garage they just put up. The entire drive and parking inside is concrete and its huge slabs of concrete so obviously hand trowling an expansion slot there would be more much more expensive than saw cutting it after the fact. Anywhere they got cracks...not many mind you...but a lot more than the smaller work they are doing without the saw cutting. Same people.

Just a side note....

Glowblue, how many "people" were working your concrete and how big in square feet in your concrete job?

I hate concrete!!!!!!I don't care how you do it or what you do you will get cracks period... surface cracks are going to happen and most builder's will have that as a guarantee in their contract

Quote: "In my office building complex, I watched them pour sidewalks and concrete curbs with the temperature about 101 and there are no cracks there either. They work fast enough they don't need any retardants."

I guarantee you they had admixtures in that concrete. You would not have seen them added, they're done at the batching plant. You cannot pour concrete in 100+ temps without them. Typically when the mix designs are submitted if it's a hot pour the admixtures are shown right in the mix design.

Maybe TXDot and cheaper commercial contractors still use hand-tooled joints, I don't really pay too much attention to road construction (other than cursing it profusely when I'm driving). None of the larger GCs that we work with (Turner Construction, Beck Construction, etc.) use hand-tooled joints. It's difficult to get a nice, straight line with hand-tooled joints. It wouldn't matter much for road construction, but commercial clients tend to be more picky about how the joints look. And these GCs don't use felt for EJ filler either :-)

No, they generally use a saw whenever the amount of concrete being poured is so large that its cheaper to cut it after the fact then have a guy on his hands and knees. Its cool when they do the roads, they have some kind of machine that rolls along. They dump massive amounts of concrete into them. They literally have 5 trucks backed up at a time. When it comes out the other end, its done for the most part. They come back with saws later.

However, for a small backyard project, a saw is expensive and more time consuming compared to a $3.00 Mexican laborer. And you are doing side walks or curbs, a saw doesn't work as well either.

If his concrete got messed up like mine, its because they only had 2 guys, really only 1 good one trying to do a pour that needed about 8 guys. They couldn't trowel the lines in because there was not enough time. So they had no choice but to cut them in. And like him, I had cracks I could see when "wet" about the second day.

The thing about concrete is there are a more people trying to do it that don't know how....a lot more than use to be.