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Faulknertw 05-16-2009 09:08 AM

Should new (one years old) concrete crack?
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My home is 15 months old. I live in Pleasant View Tennessee, just north of Nashville. The concrete in the garage was poured in Fall of 2007. There are cracks throughout the garage including the photo I attached. This piece is in a corner running from wall to wall about four feet long. I can put a piece of thin wire completely through the crack to the bottom.

Every bay in the garage has cracks running from the front wall to the driveway. These cracks were established before we moved in. Before we moved in in March 2008 the builder sealed these cracks but they came back.

The driveway also has cracks that run off off expansion joint and are separating into other cracks. The driveway was poured later on a separate date probably December 2007-January 2008.

I was told by the builder that concrete is only guaranteed to do two thing: get hard and crack. Yet my last house was 30 years old and there were no cracks at all in the garage. I did notify the builder about the cracking before the one year mark.

Any ideas? Recourse with the builder? Is it difficult/expensive to repair this?

Daniel Holzman 05-16-2009 09:22 AM

Your contractor is essentially correct. Concrete always cracks, there are no techniques to PREVENT cracking, however there are numerous techniques to control cracking.

Concrete cracks for several reasons.

1. During the curing process, concrete absorbs moisture from the mix, and changes chemically. During this period of time, which can last for months or even years, the concrete shrinks slightly, and cracks.

2. Concrete is weak in tension, therefore any significant tension forces, which can come from wind, frost heave, changing building loads, impact, or dimensional changes to attached building elements such as posts, are likely to cause cracking of the concrete.

With a floor slab, there are two common techniques used to control cracking. One is to cut relief joints into the concrete. These are generally V shaped grooves cut into the concrete at regular spacing (4 foot on center, 8 foot on center are common spacings). The V grooves "attract" cracking, allowing the remainder of the slab to be relatively crack free.

A second technique is to install wire mesh reinforcing in the slab. The mesh is not there for strength, it simply minimizes (does not eliminate) cracking. You can order concrete with special admixtures that also minimize cracking, and there are special additives such as plastic fibers that can be added to the mix to reduce (not eliminate) cracking.

Careful curing of the concrete also minimizes cracking. Proper curing involves covering the concrete with moist burlap or similar product for several days, and avoiding excessive heat or cold during the curing process.

Needless to say, most of these techniques are NOT USED in residential garage slab construction, because most people take low bid, and these techniques cost money. So the question is, did the contractor explain to you that there were options to minimize and control cracking, that they would cost you extra money, and did you elect not to go with them? Or did he just build the slab the way he normally does?

The good news is that the small cracks as shown in your photos are cosmetic problems, not structural. There is no need to repair them, unless you find the appearance objectionable. "Repair" typically would mean sealing them, either with epoxy or a similar material. This would potentially improve the appearance, but as I said, is not a structural issue.

jaros bros. 05-16-2009 02:33 PM

I have not seen concrete crack unless the base was substandard or the concrete was not properly hydrated during and afterwards. Do you have a lot of cracks? To me that is unacceptable but only because I'm really fussy. Generally this kind of thing is standard in new construction and no one raises their eyebrows too much. I have never had any of my slabs crack like that even once...but I make sure the base is compacted and has the proper material for the area, and I like to lay out burlap or straw and leave a sprinkler on it for at least a week afterwards misting it lightly every so often. Also rebar is very important. Number 4 or 5 2' on center is standard, and an engineer can help with tricky soil. The fiberglass alone has not impressed me and I have seen it crack on slabs.

JohnCarpenter 05-16-2009 10:56 PM

If I see anything more than tiny spider cracks, then the soil wasn't properly prepared. That crack would be unacceptable to me. I have only seen a handful of slabs with cracks that wide.

Johnny Jackson

yesitsconcrete 05-17-2009 01:40 PM

your contractor's trying to dodge a bullet impo,,, concrete will crack - the reason it cracks is the tension force that's applied to it during the process of hydration ( curing ),,, when its changing from plastic ( out of the chute concrete ) to solid, it transforms thru a ' green ' stage - not hard & not soft - during which time the conc's hardening,,, that's when wire mesh can add strength to the slab,,, after its cured, the wire mesh holds the broken pieces together & makes it easier to cut yourself when removing the fail'd conc :mad:

however, the mesh MUST, by ACI spec, be plac'd at the vertical midpoint of the slab +/- 5% - in a typical garage floor of 4", your allowance would be +/- .05: ( one/one-hundredth of 1/2" - impossible ),,, seeing as the jabonies ( jaboneys for those of you in rio lindo :laughing: ) walk all over the mesh, its pointless using it as its never in the right spot,,, fiber helps us ' feel better ' but is just about as useful as you-know-what on a priest impo,,, it also costs more :huh: than reg conc,,, rebar ( steel ) adds FLEXURAL strength, not compressive,,, that's why we usually put it in driveway throats subject to shock loading & on bdge decks.

the BEST way to prevent random cracking is ( odds on favorite ) cut the control jnts at the right time & use a correct jnt pattern,,, this tells the conc to crk where WE want, not randomly,,, its possible your crk came from early loading - said jaboney (ie) backing onto the fresh slab w/heavy pickup but my $$'s on the jnts,,, keeping slabs NO MORE'n 20xslab thickness as express'd in feet would comply w/another aci regulation, too.

since conc expands/contracts as a solid in reaction to temp, your crk MAY now be a jnt so don't be surprised if the crk starts spalling,,, the ' spider ' cracks ( crazing ) usually mean the finishers ' bless'd ' the screed'd surface w/addl wtr to prevent it from setting up too soon as guido/bo/bubba called in sick that morning :laughing: so the crew's a man down :furious:

the bad news is the crk probably conforms to acceptable limits of work,,, the worse news is, as holzman stated, the bum gc used a cheap crew OR his guys're ignorant/stupid/lazy,,, the other bad news is conc likes to be square which probably accts for your other random cracking altho it could also be soil prep as jack/jarros post.

if i were you, i'd be looking at my homeowner's warranty quik,,, too much random cracking's unacceptable !

Gary in WA 05-17-2009 02:13 PM

30 years ago they probably ran the water supply under your house (meters located anywhere), not in the garage. These days, usually, the water meters are near the property lines, and water supply run into the garage (close to power, cable, etc.).
So there is more trenching involved, more back filling of the garage area. Putting dirt back into a hole requires special needs. Any protrusions through the slab require special attention. As mentioned control joints, proper mix, etc. Those cracks are wide, unacceptable to me. Be safe, G

Faulknertw 05-18-2009 01:18 PM

Reply to all ref: should-new-one-years-old-concrete-cra
Thanks for the insight. I really appreciate it. Knowing that it is not a structural issue helps, although it is unsightly. I'm fairly sure the builder will not do more than repair with epoxy, which is what he did initially with the cracks noriced during the pre sale walk through.

Take care

yesitsconcrete 05-18-2009 01:44 PM

i'd guess the garage floor slab ' floats ',,, whoever coated the garage floor can ( or should be able to - ) sawcut the crk, seal it correctly, diamond saw a correct jnt pattern, AND place another coat of wtr-bas'd epoxy.

UpComingBuilder 05-18-2009 04:21 PM

They probably did not hydrate it enough. Or they might not of done it at all. You should contact the company definatley ASAP

jomama45 05-18-2009 06:23 PM

Unfortunately, the OP's problem is pretty common in new construction. It looks like the crack is stemming from the garage door opening. We've learned thru time that you either have to run a joint right to those corners, wrap them with expansion joint (like 1/2" sill sealer type material), or better yey, do both. Ocassionaly, a HO or builder thinks I'm crazy for running joints off on strange tangents, but after I explain the reasoning, it's always accepted. The main reasons for the cracking in the photo are #1, as Yes stated, the concrete slab has a corner, deviates from square, & thus a natural relief is created. #2, and more importantly, as the slab shrinks as a whole, the slab is locked in place by the concrete wall it is sitting directly against, & has no way to move at all at the control joints. As for the OP, I get a sense that they didn't put any control joints in the slab at all? Either way, if this is a slab inside (separate) from the garage foundation walls, it's not strutural, & only a cosmetic problem. It can be irritating to deal with "new" cracked concrete, but in my experiences, the best thing you can ask the builder is "would you want this at your house?"

Good Luck.

yesitsconcrete 05-19-2009 05:40 AM

my driveway's less'n 2yrs old & i've got a random crk - so what if it only measures .002 now - its THERE & i take it personally :mad: how DARE it ? ? ?

in fairness, i didn't place, finish, OR jnt/saw it 'cause i was too busy doing the same work in augusta for 3x what my guy here charg'd :thumbup: so i'll live w/it,,, IF he'd only cut the jnts WHEN i told him instead of coming back the next day but that's crying over spill'd milk,,, someday, if it starts acting as a jnt & spalling, that slab'll be replac'd,,, then again, IF frogs had wings, they wouldn't bump their *** when they tried to fly across the floor, right ? ? ?

my garage's another story - NO control/expansion/isolation jnts in a 3-car - you can only guess how many random crks as the conc tries to lessen expansion/contraction stress - spalling's common as the crks act as jnts,,, i don't feel insulted 'cause it was that way when i bought it,,, when i o'lay the garage floor, i'll ' weld ' the crks & diamond-saw full-depth controls to resolve it - IF i get time to work on my own :whistling2:

repairs & decorative overlays are our work but its like the shoemaker's kids :laughing:

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