# Large Concrete Crack repair - detached garage.



## alecmcmahon (Apr 30, 2010)

I have some fairly large cracks through out the pad of my detached garage pad.

Most of them are toward the garage door, i assume they started as small cracks, neglected winter after winter and they just expanded.

I just moved in this spring, so i'd like to get this fixed up before this winter, and hopefully do some sort of expoxy treatment.

The worst of the cracks are pretty big and deep, and go right down to earth. I also have some other cracks the previous home owner repaired, the pad cracked and raised in some spots, so they are at different heights. 

I'd like to properly fill these cracks, and float out the uneven areas, What products / methods would you guys reccomend to properly take care of these cracks the right way? I'd also like to expoxy the floor after this is taken care of :

Pictures:









( height difference, note ladder legs )


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## Daniel Holzman (Mar 10, 2009)

These are large cracks, and are almost certainly due to improper preparation of the subgrade below the slab. Poor subgrade preparation allows the slab to settle differentially, which can lead to large cracks such as you have.

The best way to permanently fix the problem would be to jackhammer the existing slab, and install a proper subgrade, which would typically consist of 6 to 12 inches of compacted crushed stone. This is a lengthy process, and you may not have the time, money or energy to do this.

The cracks can be filled using either ordinary concrete, modified concrete, or epoxy mix. In all cases, the cracks must be cleaned thoroughly, which generally requires pressure washing out all soil and other foreign material. You can then place the epoxy mix or modified concrete according to manufacturer's instructions. The Thoro corporation has a whole line of special concrete mixes for just this purpose. The Sika corporation has a line of epoxy mixes that can be used for filling concrete.

Recognize that simply filling the cracks will not provide permanent relief, but a few years may be all you need.


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## alecmcmahon (Apr 30, 2010)

I wouldn't doubt that the sub pad is improper, but digging anything up is out of the question, i just dont have the money , time, or effort to put that sort of work in. Plus, it wouldn't be worth it. The house was built in the 1950's and i wouldn't doubt that the detached garage was built then either.

Just looking for a fix that would slow down / stop the expanding so that i can sort of finish up the garage and set up shop.


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## concretemasonry (Oct 10, 2006)

Can you tell is it is slab with a thickened edge? If it is there would be cracks in the edge of the foundation.

If it is a floating slab inside a stem wall system the supports only the walls, the correction is easier and cheaper. You can usually spot the difference if it has a stem wall projecting above the slab (for drainage and cleaning) and separation of the wood from the surrounding soil and no cracks. This is a better way to do it because of the long term benefits and gets the wood above the surrounding grade.

One of the problems is that that type of garage slab (attached or detached) is it is usually poured after the garage is up and the soil can be uncompacted and can contain construction debris. The good news is that it is a one day job for contractor with a skid steer to rip out the floor and bad soil, compact some good gravel and pour a good slab and a new apron slab. I am in a townhouse community that had a few isolated floors (2 car, 26' deep attached garages) with similar cracking and settlement. Because of the location of the cracking the contractor charged the association $2000 to make a saw cut between the good and bad and remove the front half of the 2 car slab for about $2700 to do the complete floor. It was amazing to see the beer cans and rotted drywal that came out when they dug.

Dick


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