Concrete experts please look at these cracks

[gearhead78]

I am scared to even show these to anyone but I need to to sleep at night.

I used pretty much all my savings to build a 42 x 50 building behind my house. In the long run I hope to be making some money doing side jobs and using it as a personal hobby shop soon. I had the whole thing contracted out and I am already having a huge problem because they did the gutters all wrong and I get water running down my walls in a hard rain. I have been trying for 3 weeks to get that resolved and still have not been able to get the sub out to fix it. Worst case I know what it will takes to fix the walls and it is something I can do myself but I am hoping they are still going to fix it. He keeps saying he will fix it he has just been tied up.

That all being said I might have a much bigger problem that I am sick to my stomach about. I am getting random cracks all over the floor. The poor is about 3 months old now and the building was put up about 2 weeks after it was poured. The slab is 5-5.5" thick with rebar and it was stood up on stands. I don't see any uneven areas but many cracks are wide enough to catch my fingernail in.

Here are a bunch of pictures. I added the penny to get an idea of size. One of the cracks runs pretty much under where one on the legs of where my 2 post lift is going. Someone please put my mind to ease that these are just normal shrink cracks and I don't have a real structual problem.

[miketyler]

I'm no pro but I think most will tell you cracks happen all the time. On a visible slab, they usually put reliefs in so when the slab settles, the cracks will form at the reliefs. Your shop was metal construction? I would bet even if the slab does drop the metal design probably will be a lot more tolerant than stick construction. If it does bug you, call a foundation company and have them come out and check it to make sure its all on plane.

[Vertnut]

I wouldn't panic. A lot of things can cause those cracks. It was poured in the winter, for one thing. Good concrete men use additives to compensate for humidity and temperature. It looks like it's curing out now that we're warming up. Rebar doesn't mean much unless it was engineered by a certified structural engineer, neither does the slab "thickness".
I use a 4000psi mix with the fibers in it, even though my engineer calls for a 3000psi mix. I can't afford to have too many visible cracks due to homeowners freaking out.
More than likely, it's more cosmetic than structural. As Mike stated, the load it has on it is nothing compared to sticks and bricks.

P.S.- I deal with guys all the time that think they can save money by building their own house. This is a small scale example of why it rarely works out the way they think it will. Can you imagine if you were showing me the floor of your new $350k house and you had water pouring in the walls? It happens all the time.

[ceyko]

Others are more qualified then I am, but I can sure as hell see why you're freaking out. Those shops are not cheap either.

[gearhead78]

I wouldn't panic. More than likely, it's more cosmetic than structural. .

I'm not happy its looking like this but that is my primary concern. I just want to get back to car building and have this "building" building nightmare behind me.

[83coupe]

As long as it doesn't look like this I wouldn't worry about it. Small cracks are normal..

http://foundationrepairokc.com/wp-content/uploads/mudjacking-slab-crack.jpg

[forbes]

concrete does 3 things after it's poured. get hard, gets lighter and cracks.
those are just surface cracks, with it being poured in the winter (as some one mentioned above) we use accelerators so we don't have to finish all day. what that does is make the concrete flash (start a chemical reaction to harden) that in turn brings the milk (wet stuff to the top). You could get some Ardex and fill it and never see it again if it bothers you that much

[gearhead78]

concrete does 3 things after it's poured. get hard, gets lighter and cracks.
those are just surface cracks, with it being poured in the winter (as some one mentioned above) we use accelerators so we don't have to finish all day. what that does is make the concrete flash (start a chemical reaction to harden) that in turn brings the milk (wet stuff to the top). You could get some Ardex and fill it and never see it again if it bothers you that much

So if one of the legs of my lift needs to go on top of a crack like that its OK?

[dumpycapri85]

The rule is to let it cure for 28 days before building on it but NOBODY does . You will have cracks that will open up and close but as long as one side is not higher then the other it is pretty normal .

[Unicorn Jeff]

The rule is to let it cure for 28 days before building on it but NOBODY does . You will have cracks that will open up and close but as long as one side is not higher then the other it is pretty normal .

x2

[turbostang]

I don't know much about concrete pouring/repair etc.. but I ask this, when have you seen ANY concrete that was NOT cracked?

[Broncojohnny]

I don't know that much about how concrete cures even though I have poured a few slabs in my lifetime. I do know that my company owns around 450 industrial buildings all over the country and I read tons of reports from structural engineers and third party consultants. None of those pictures would even make me bat an eye. Now, if it buckles and one side of a crack is higher than the other, you got some problems, but even then in a warehouse or car shop type of application it isn't the end of the world, slabs can function just fine for decades with massive cracks in them even with thousands of pounds of forklift & freight rolling on top of them. At the very worst, you call in someone to amke some cuts, jackhammer the shit out of it and re-pour it. Really it is a cosmetic issue as vertnut said.

[gearhead78]

Thanks for the input everyone. Here are some new pictures so you can see exactly where they are. I used tape to mark them and took pictures from the roof at the LH front of the building and went clockwise around the shop. Not all of them I marked are as bad as the close ups but 50% or so are. Others are just barly visible. The big square next to the tool box is the apox spot for one of the legs of my lift. I really don't want to change where I mount it.