crack in house slab noticed

hi all, just wondering if we (my partner & I) should be concerned after noticing a crack on the concrete house slab (hairline) which runs from a bedroom into the main lounge dining area of our current house which we are building. The house slab was layed in March and we are a month off completion/final inspection. The carpet layers have not been in as of yet hence how we saw the crack. The main lounge dining area has been layed with ceremic floor tiles already. Any help on what to do would be greatly appriciated.

I don't know where you are located or anything but
I had a crack in my slab that ran from bathroom, across the hallway finishing up about the island bench. When I mentioned it to my SS he said unless they are wider then 5mm it is just a surface crack and they will not do anything about it.

My point is give your SS a call and mention it, before the carpet gets laid so he can actually see it.

My personal theory is that it is possibly just above the water pipe that runs from bathroom to sink in island bench (as it is more or less a straight line) but I don't know how true that that is.

I have been living in the house for 5 months and the crack has not gotten any wider or longer in that time so I don't think it will be an issue for me.

My tiles are going down this weekend so no one will be able to see it after then anyway. YAY

A 4 mm crack in a slab would be a disaster!!!!

The Guide to Standards and Tolerances 2007 (Building Commission VIC) indicates that slab cracks greater than 2mm are defects. Hairline cracks <.3mm are insignificant. Anywhere in between should be monitored for a year.

We have several hairline cracks in our garage slab, which I'm not worried about, and also some in our driveway, again not a concern. There is one particular crack in our driveway that is an issue however. Even though we have been in our house for 21 months we had the maintenance guy here yesterday (he's new - and fantastic) finally finishing off some minor stuff (door latch adjustments etc) but the main reason we wanted him here was to monitor the widest crack in the driveway. He has taken photos for reference. His motto is that the crack is a concern if (1) you can stand a 20c coin in it, and (2) if, at the junction of two cracks, little 'islands' of concrete are created, like this:

We are not overly concerned at this stage, at least officially our builder now has a reference to go by.

Ouir driveway was included in the contract.

Great info - in fact I just measured a 20c coin, and it appears to be very very close to 2mm thick!

Can't wait to get home tonight and try the 20c coin trick

I cant believe that the concretor who done that driveway couldnt have at least put expansion foam between the brickwork before the concrete was poured. It would have prevented it from cracking.

Did they put saw cuts on the concrete? Because that also helps to eliminate cracks from occuring.

The lack of foam was immediately noticed by the maintenance guy.

There are plenty of saw cuts in the driveway, the largest hairline crack runs diagonally across one of the sections, corner to corner....

Hey Eager, how did you or your builder resolve this? I'm having the same issue as well.

No, the cracking never got any worse so we didn't bother making an issue about it.