Foundation a new construction is cracking. (where is)

[Houston321]

I constantly get this question. Great answer CHDOC. As with anything to do with construction & real estate, everyone...especially "friends" have an opinion. That is why I had a concrete expert - structural engineer - type this up...and I give it to customers every time they complain about cracks:

I often get asked about cracks in concrete foundations. Many home owners are nervous when they see cracks in concrete and wonder if they are bad or dangerous. While it’s a natural reaction to be concerned when you see something cracked the reality is that 95% of cracks in concrete are harmless and nothing to worry about.
Why Does Concrete Crack?Concrete cracks when it is subjected to tensile stress (forces that pull apart on something vs forces that push together something). Concrete has very strong compressive strength and very poor tensile strength. That’s why concrete is reinforced with steel reinforcing called rebar. So you end up with a composite material, the concrete takes the compressive loads and the steel rebar takes the tensile forces.There are many factors that cause concrete to crack. Some of the factors that can cause concrete cracks are:
Drying Shrinkage – as concrete cures and goes through it’s chemical reaction between the water and cement particles it begins to “dry” out. As with most materials that dry out they begin to shrink causing hairline cracks to appear.
Thermal Shrinkage – all materials shrink and expand with changes in temperature. As concrete cools down (the chemical reaction that’s created when water and cement is mixed creates heat) it shrinks. The shrinking from cooling down can also cause hairline cracks to appear.
Restraint – This topic is a bit harder to explain but it’s caused when concrete is confined and prevented from moving due to the structure. If the concrete wants to move due to loading, thermal or other effects and it’s restrained from doing so it will crack.
Settlement – If the ground around a foundation settles it can cause the concrete to crack. Settlement can cause significant damage under certain circumstances.
Loads – As I mentioned when concrete is subjected to loads that cause tension it will crack the concrete. Tension can be caused by many different loading conditions and it’s best dealt with by designing reinforced concrete that uses rebar.
Corrosion – When steel rebar corrodes inside of concrete it expands and causing the concrete around it to crack.
Which Concrete Cracks Are Bad? Obviously this is a topic that has many answers and not easily answered in a simple way. However, what you need to know is that ALL concrete cracks. In fact, reinforced concrete must crack before the rebar can take hold and do it’s job. Most cracks are so narrow that you can’t see them unless you look very closely with good light.
So which cracks are bad? Typically if you see a concrete crack that’s less than 1/8 inch wide then I’d say you can totally ignore it. If you find a crack that’s between 1/8 inch and 1/4 inch wide it is most likely nothing to worry about. In this situation it’s important to look at the concrete on both sides of the crack and try to determine whether or not there has been any relative movement between the sides, up/down, left/right, in/out. This would be an indication of settlement and therefore a potential problem.
If you have a concrete crack that’s 1/4 inch wide or wider then I recommend you contact a local structural engineer. Cracks of that width indicate significant movement within the foundation and warrants further investigation.

[CityScout1]

Thank you Houston 321 for the information. This is very helpful and excellent info. A few days ago they tighten the cables on the slab and it appears that the crack as closed up just a little. We'll keep an eye on it, especially when they start putting on the concrete tiles.

Thanks again

[arubaatori]

I believe I have the same issue. They haven't stressed the slab yet. They did start the frame work two days after the pour. Now they have the second floor and roof up already. I'm waiting to talk to the engineer who is responsible for the slab. I know most people said it's normal, but I looked around 10 other new constructions and none of them had crack like yours and mine that goes from one end to the other. I know after the pull the gap will probably close, but I still want the engineer's proof that the slab will perform. Plus I believe they'll have to seal the crack too.

[marksmu]

Its after the fact, but regardless of what anyone says, post tensions slabs in Houston are a bad idea. Builders like it b/c its cheap and easy, but if you wanted a rock solid foundation you should have insisted on piers with grade beams....too late now. Builders don't tend do these except in expensive homes b/c they cost about 30% more.

Engineers will tell you that everything is fine with post tension and also reinforced concrete, but in expansive soil, if you don't have piers and grade beams tying it all together, its not so much a matter of if you will have problems, its when. Most new slabs are on compacted select fill so they tend to last 10-18 years without issue...Its funny how the duration of the performance of the foundation just happens to exceed most builders warranties.

I am however of the opinion that your cracks are non-structural surface cracks as stated above.

[astrohip]

Originally Posted by marksmu

Its after the fact, but regardless of what anyone says, post tensions slabs in Houston are a bad idea. Builders like it b/c its cheap and easy, but if you wanted a rock solid foundation you should have insisted on piers with grade beams....too late now. Builders don't tend do these except in expensive homes b/c they cost about 30% more.

Post tension is not a bad idea. Is it as good as piers & beams? No, but as you say, it costs less. And a properly done PT slab can last decades.

It's like everything else, if we built using only the best technology & construction techniques, only the 1% could afford a home. But using less expensive methods makes homes more affordable for all. The trick is making sure less-expensive still equals lasting quality. And in most houses, it does.

Expensive cars have a fancy ant-skid system that makes it almost impossible to slide sideways in the rain or ice. Yet 80% of cars don't have it. Why don't we mandate it? Because it adds a couple hundred in cost to a new car.

So you've upgraded the slab, now you require a better window, then a better lumber grade. Then trusses instead of whatever. Now that $150,000 home costs $210,000, and you just priced 30% of home buyers out of the market.

All of life is a compromise. The trick is in the balance.

[marksmu]

Originally Posted by astrohip

Post tension is not a bad idea. Is it as good as piers & beams? No, but as you say, it costs less. And a properly done PT slab can last decades.

It's like everything else, if we built using only the best technology & construction techniques, only the 1% could afford a home. But using less expensive methods makes homes more affordable for all. The trick is making sure less-expensive still equals lasting quality. And in most houses, it does.

Expensive cars have a fancy ant-skid system that makes it almost impossible to slide sideways in the rain or ice. Yet 80% of cars don't have it. Why don't we mandate it? Because it adds a couple hundred in cost to a new car.

So you've upgraded the slab, now you require a better window, then a better lumber grade. Then trusses instead of whatever. Now that $150,000 home costs $210,000, and you just priced 30% of home buyers out of the market.

All of life is a compromise. The trick is in the balance.

I don't disagree with anything you said cost wise...but - I am of the opinion that the foundation is the ONE place that a builder should not skimp at all. Can you build it for less another way? YES - should you? No - Im ok with cheaper windows, doors, ac, insulation, whatever else you want - but at least build the best foundation. The foundation (when concrete) is the only part of your house you can't easily replace - literally every other system can be replaced or upgraded later.

Foundations can be repaired, and most post tension homes built 20-30 years ago, have been repaired, but the cost to repair exceeds the cost to just have done it right the first time.

I recognize pricing is a fine line with builders - but that is because consumers are idiots. They would rather have a house with fancy appliances and granite that will look nice for a few years, than one with less expensive appliances and counters that will stand the test of time structurally.

Builders are selling what people are buying and its all image. The builder is off the hook by the time the problems arise.

[astrohip]

And I don't disagree with any of your points. Well said.

[Mandres]

Originally Posted by marksmu

Foundations can be repaired, and most post tension homes built 20-30 years ago, have been repaired, but the cost to repair exceeds the cost to just have done it right the first time..

I'm always been under the impression that there is no way to permanently repair a slab once it has settled/cracked. Mudjacking is a bandaid solution that lasts a few years, but once the bearing soil has failed you basically have to live with the result. Is there a new repair procedure that works long term?

Monolithic slabs are terrible foundation choices for Gulf Coast soils, but it's really hard to find a builder with the knowledge/willingness to do anything else.

[Jerry100]

Originally Posted by arubaatori

I believe I have the same issue. They haven't stressed the slab yet. They did start the frame work two days after the pour. Now they have the second floor and roof up already. I'm waiting to talk to the engineer who is responsible for the slab. I know most people said it's normal, but I looked around 10 other new constructions and none of them had crack like yours and mine that goes from one end to the other. I know after the pull the gap will probably close, but I still want the engineer's proof that the slab will perform. Plus I believe they'll have to seal the crack too.

My house slab got the similar cracks. What did the builder do for the cracks in your house slab?

[Chheng0000]

Hello I'm just curious the outcome of this after several years later. Just had slab poured and same thing happened where is is cracked in the middle all the way down to the dirt