Concrete Expansion Joints- Not Enough? & Concrete Crack Repair

by New Home Buyer
(Pleasant View, UT)

Q: I have a house under construction currently. Our 3rd car garage is cracked right down the middle of the full length of the garage, and approx 30' long. Would this be caused by the lack of expansion joints? If so, what are my options to fix the slabs in the garage. I understand concrete cracks, but this seems a little much. The builder says it it is what it is...that's the nature of concrete. I just want to know what my options are? We have expansion joints saw cut N. To So., but not E to W.

A: Dear New Home Buyer,

Thanks for stopping by my site!

Even though I've always hated the saying "it is what it is," it certainly is the nature of concrete to develop cracks, plus, sometimes you can do everything right and still end up with cracks. Sometimes it has to do with things like shifting and settlement of the ground underneath your concrete pad, and even things like weather conditions during the curing process. That said, when putting in large expanses of concrete, there are a number of things that can be done to minimize, but not completely eliminate the possibility of cracks.

Of course, expansion joints are your main defense. You didn't say how far apart the expansion joints are, but the general rule of thumb is that expansion joints should be spaced in feet no more than two to three times the slab's thickness in inches. Therefore, a slab that's 4 inches thick should have joints spaced at most 8 to 12 feet apart, and they should be cut to one-fourth the depth of the slab, which, in this case would mean joints one inch deep.

Concrete Pavement Research & Technology has a document that you can read at http://www.pavement.com/Downloads/RT/RT6.03.pdf that is actually about the placement of joints in concrete traffic roundabouts, but there's a lot of good information contained in it. While their advice may be overkill for the standard residential driveway or garage, there is plenty of food for thought. For example, here are a few things on their list of Things to Avoid:

● Slabs less than 1 foot wide

● Slabs greater than 15 feet wide

● Joint angles of less than 60 degrees (which shouldn't be an issue in your case)

● Creation of interior corners by making L-shaped slabs (which also shouldn't be an issue)

For concrete roundabouts, some government agencies require that a contractor submit a concrete jointing plan prepared according to recommendations of the American Concrete Pavement Association (ACPA) recommendations.

The ACPA has a number of "dos and don'ts" listed in another document you can get online at

http://www.pavement.com/cpp/2008/CPP-06-08.html#3.

In it they mention that transverse and longitudinal joints are necessary for controlling cracking in concrete pavement, so your comment that you placed expansion joints in one direction, but not the other may have something to do with the cracking you experienced. Typical maximum joint spacings are 15 feet for transverse (across) joints and 12 feet for longitudinal joints, though it depends on the thickness of the concrete and what type of sub-base it was placed atop.

You didn't mention the thickness of the slab used in your garage, but unless your contractor clearly spaced the expansion joints improperly based on the slab thickness, your main option is simply going to be to have the crack repaired.

For narrow cracks of 1/8 inch of less, you (or your contractor) will chip away any flakes or loose pieces of concrete, then scrub it with a wire brush to get rid of debris. Then, the crack is rinsed out, and concrete patching compound with latex additive is troweled into the crack. It's smoothed out and feathered while the compound is still moist because this stuff sets up quickly.

Larger cracks - 1/4 inch wide or more - will require caulking or sand packing. Caulking will self-level, so you won't need to smooth the surface, but you might have to make multiple applications. Sand packing is used with concrete patching compound, preferably with a latex additive in it. You pour in a layer of sand, then use a trowel to apply the patching compound. You have to smooth it quickly and feather the new surface to the edges to give it a finished look.

Even bigger cracks than that may mean you should call in a concrete professional who can do a risk assessment to see if there is some structural problem that needs to be addressed.

But whatever you do, don't just neglect the crack. It's often a case of "a stitch in time saves nine."

Good luck,

Alan
Meet-Mr-Concrete.com
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