When can concrete start to get cracks?

[ron in sc]

If concrete is going to crack will it start to do so within any specific time frame after it's poured? Or can it start cracking just about anytime?

I had concrete poured 13 months ago and so far no cracks. My foundation is a stem wall system with rather substantial footings.

 

[ddawg16]

I have very limited experience with concrete....but what I have seen....
'Issues' ususally show up in the first few weeks....
As I understand it, concrete is about 90% cured after 28 days (magic #)...but continues to cure over the life of it...with many variables...especially moisture and temperature.

I would speculate that you did well...no cracks yet... Sounds like you did a good job....will you ever get cracks? I don't know......but with each passing month I would say the odds are less and less.

 

[toxicz28]

There are alot of factors that make it hard to determine if and/or when it will crack. I've seen concrete cack after a few days, and after a few years. So there is no set time to say when it will no longer crack.

 

[rsanter]

the rule of thumb I have always heard is that there are two typrs of concrete.
the type that IS cracked and the type that WILL crack

many track houses have cracks in the slab within the first year

bob

 

[Charles (in GA)]

My slab was poured in October of '99. About three years ago, a couple of hairline cracks showed up radiating from stress points, where the door track was anchored in the slab.

Other that it is pretty much crack free. I do expect more to show up, concrete takes up to 50 years to fully cure (Yes, you read correctly) so its not unexpected to have cracks show up five or ten years after it was poured.

Charles

 

[jimvannoy]

I'd say it can crack within the first week of being poured to 50 or more years later. Depends on a lot of stuff.

 

[Printer Mike]

If good concrete is reinforced properly, has a steady base and proper expansion joints, I can't see any reason for it to ever crack.....

In 40 years, I have never had any like that!

Someone needs to come up with, "The cracked look finish!" lol

 

[boiler7904]

No major way to tell when or if concrete will crack. If you could do that, you'd be a very rich person in the construction industry. Bob is right about the two types of concrete. Cracking is one of the two things concrete is guaranteed to do.

It can start cracking on day one if the control joints aren't in the right places. You can also get stress cracks or load-imposed cracking. Unless something happens down the road to the base (like water intrusion and movement), you should have too many problems from that aspect. Unless you plan on driving a semi on a 4" slab or dropping 1000 pound loads on a regular basis, that won't be a problem. That leaves stress cracking as your main source of potential cracks and there's nothing you can do about that but anticipate where they will form and cut joints there.

Like it was said before, concrete gets to about 90% of the design strength within the first 28 days unless there are extenuating circumstances. Since concrete cures by hydration, it never completely cures. The lime in lower portion of the slab will take longer to fully hydrate since water near the surface evaporates so fast.

When I took out my 2 year old concrete patio this spring, the bottom half was dark gray like fresh concrete and was somewhat softer / easier to break than the top portion of the slab.

 

[Vinko]

If good concrete is reinforced properly, has a steady base and proper expansion joints, I can't see any reason for it to ever crack.....

In 40 years, I have never had any like that!

Someone needs to come up with, "The cracked look finish!" lol

I just had a concrete "ramp" poured where there had been asphalt. The concrete will need to support container trucks with 20,000 lbs. or more. Every 6 inches we did #5 rebar. 300 sq. ft. area total. Went at least 6 inches deep.

I had the guy who was widely considered the best in town do it. He did our other bay area at the loading dock in 1985 and still no cracks over 20 years later. And it sees use 5 days a week from at least 10 trucks a day.

 

[Benchloader]

Depends on care and method with which it is poured.

My parents home in MI has driveway as old as me (over 50) with no cracks any where. it was poured on a good prepared base with re inforcement bar & wire net.

Where I live now in LA they poured fiber reinforced concrete directly on the clay surface. No other prep at all. Cracked first time it was driven on 3 days later. Now there are more cracks than can be counted.

 

[BuickFarmer]

"Typically" if concrete is going to crack it will do so within the first year or so. It has gone through a period of expansion in the summer and contraction in the winter. Contraction and expansion are probably the number one cause of cracking i a properly poured and finished slab. If you get an extremely hot summer or cold winter after the first year it could still crack. Proper curing is the most critical thing. If it was poured 6 inches thk with 3000 psi concrete, jointed correctly and sprayed with a membrane type curing compound and not allowed to dry out within the first 7-14 days, it should be fine.