Hair line crackings in garage floor post tension slab

Hi all,

I just bought a new townhouse and when I moved in I did not have inspector visit assuming that new house will have less trouble (boy I was in for a rude awakening).

I just moved 2 weeks ago and I saw some hairline crackings in the garage post tension slab concrete.

The crackings are randoms so they are not one of those controlled points.

Do you guys think this is normal crackings or I need to contact my builder to fix them?



Sounds like normal concrete shrinkage/curing cracks, even for a post-tension slab. However, some more information would be helpful. “New” meaning how new? How wide and how long are the cracks.

Common shrinkage/curing cracks are caused by many things, so guessing the cause here is a shot in the dark.

Do your neighbors have the same conditions? Presuming that their houses are also new and that yours is not a new house in an old neighborhood.

I apologize for lack of info since I am kind of newbie of “home owning”.

The cracks are varied in length. In average its about 10-20" in length.
There is one about 30" which start from the center of the garage entrance and going left to the wall of the house.

But all of them are hairline in wide (less that 1/64 ").

I have been trying to post pics but my camera seems to have problem capturing the cracks. I will post them once I am able to get focus pics of these cracks.

My house is in new development area which are finished last year.
All the houses in this complex are new.

I saw at least 3 houses in the complex have the similar crackings in the slab. However some of them have perfect concrete slab. =(

Will these crackings be getting worse and cause problem to the foundation of the house? Also will they casue humidity problem or leakings (the water from the ground infiltrated these cracks)?

Thanks for the reply guys, I really appreciated.

  • Henry

Hairline cracks are typical in any concrete slab.

If these cracks worsen over time, then I’d consider getting a PE to evaluate your situation. As for the repair method for now, if water can seep into these cracks then you may want to have them properly sealed to prevent any moisture from seeping into these cracks which will rust the embedded tension cables and in turn, worsen the situation.

Are all concrete will crack (inclusing post tension) or I am basically unlucky to get this house?

I am just keep asking myself had I have chosen different unit, it may not have this crack in the garage floor =(

How do I know if they will get worse, ie: will I have to keep watch them closely over time?

  • Henry

Show me a concrete floor that does not have hairling cracks and I will show you a twig that is not made of wood.

Post Tensioning or normal concrete floors will crack as you described two hours after it was poured. Even before saw cut control joints are attempted at times.

I would not be alarmed at cracks of this magnitude but would monitor and make sure that any excessive shrinkage that might endanger the post tension cable system should be sealed accordingly.

Jeff Pope would be the one to further elaborate on this subject and will most likely kick in when he sees this Post.
In the mean time, I don’t believe you have anything out of the ordinary for a concrete floor.

Good Luck.


Cement is spelled C-R-A-C-K…

…from my disclaimer…

Many slabs are found to contain cracks when the carpet and padding are removed, but there is no absolute standard for evaluating them. Those that are less than 1/4" wide and which exhibit no significant vertical or horizontal displacement are not regarded as being structurally threatening. They typically result from common shrinkage, but can also be caused by a deficient mixture of concrete, deterioration through time, seismic activity, expansive soil (such as clay—and the Ohio Valley has a lot), and poor drainage, and if they are not sealed they can allow moisture to enter a residence, and particularly if the downspouts discharge adjacent to the slab.

Cement is spelled C-R-A-C-K…

Jae, did you mean concrete? Cement is what they add to the sand and course aggregate to make the stuff.

Marcel :slight_smile: :slight_smile: :wink:

Yeah… (man I didn’t know he was going to get so technical…)

as homer simpson would say “doe”

or as jae might say “that would equal 24 %”:wink:

hmm, i’ve seen that somewhere else before:D



How do I know whether the cracks are because of common shrinkage or bad implementation of the post tension slab concrete?

If I asked the builder’s contractor I bet he would say normal shrinkage automatically.
Should I hire home inspector to take a look?

  • Henry


If you really want peace of mind regarding those post tension slab cracks, go here and enter your zip code and it’ll give you a list of NACHI inspectors in your immediate area. You then have the option of having the inspector of your choice call you right away. Or simply send that inspector an email.


As you’ve read in the earlier posts, all concrete will crack. A 1/64" crack in a garage floor would not be considered serious by a concrete man. There are so many variables in concrete especially when comparing to your neighbor’s. Some factors are the temperature on the day of the pour versus your neighbor’s. Other factors are the actual mix of the concrete.

Always monitor, but just realize that many concrete cracks are superficial.

Enjoy your new home.

Some cracking is superfical, and some cracking is the first signs of a problem … more so with new construction or a crack that has recently appeared or is active. If there is a concern a specialist should look at it to make the call.

JMO & 2-nickels … :wink:

How do you know its post tension concrete slab?

I’m not sure about where you live but in Florida 90 percent of the garage floors have hair line cracking.
With post tension slabs Re-bar is seldom used throughout the slab. Consequently, although post-tension slabs will generally hold together, they have a higher propensity for cracking than do slabs built with plenty of re-bar.

Actually, that’s not true. PT cables are used to compress the concrete and reduce cracking, whereas rebar is dormant until the concrete cracks.

Although hairline cracks are common in all concrete, they become more of a concern in PT slabs. For cracks to form in PT slabs, they must fist overcome the compression created by the cables.

If they are indeed “hairline,” and there are relatively few cracks, I wouldn’t be too concerned. Without actually seeing the issue, it’s difficult to make any definitive statements.


But it takes a conscientious builder, conscientious concrete pourers, and proper technology to prevent hairline cracks. There are several areas here that have been built since 1994 that have no hairline cracks. However, there are, indeed, some other areas where there are, indeed, lots of hairline cracks, also built since 1994. And the difference in cost of the houses? Oh, about a million dollars.

I agree … :wink: