Joints for interior slab

Old 01-24-06, 11:04 AM
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Joints for interior slab

I'm about to pour a 8x14 monolithic slab/footing for an addition. The slab will be enclosed (cooled and heated), and will be covered with tile or carpet. I asked a contractor friend about control joints for that size of slab, and he suggested that since it will be an enclosed slab that will be covered with flooring, I don't need to bother with control joints. Rather, I should wait for it to cure and let the slab crack on its own.

My (admittedly limited) understanding of concrete is that control joints are a "good" thing, and that a slab of the size I'm pouring would typically have a joint or two in it. I do understand that the control joint is simply a pre-determined point for a crack to form, so I my friend's reasoning sort of makes sense.

So: should I joint the slab, or just let the concrete decide where it wants to crack?
Old 01-24-06, 02:02 PM
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If it's getting a floor covering, just let it crack and cover it up. It may not even crack at all. If you want to put a control joint in, cut the floor width ways so you end up with 2 8x7 sections.

Old 01-24-06, 04:25 PM
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When I had my shop floor poured, the guy who did it gave me the option to save a little money and cut my own control joints. He said very matter of factly the floor will crack. You just have to tell it where to crack. So I cut a 3/4" deep kerf along a snapped line with a concrete blade in my old saw, and if it has cracked, it stayed within the confines of the joint he told me to put in. Very neat job.

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