Concrete Mix, Slump Test

How would you define slump?
According to the Tennessee Ready Mix Concrete Association, slump is a measurement of concrete's workability, or fluidity.

It's an indirect measurement of concrete's quality, states Gabriel Ojeda, president of Fritz-Pak Corp. in Dallas.

And Joe Daczko, group manager of concrete technology for Degussa Admixtures Inc. (formerly Master Builders) in Cleveland, maintains it's a measurement for consistency, both from a quality-control perspective and to determine how fluid or stiff a material is.

However you define it, though, the bottom line remains the same: Slump is a test for the rigidity of uncured concrete. Lower slump concrete is very stiff, and higher slump concrete is more fluid.

Most people in the business agree that a typical slump for ordinary decorative concrete applications would be in the 4- to 5-inch range, but there's no hard-and-fast rule. “The slump should match the application,” says Daczko. “It could be anywhere from 1 to 10 inches depending on what you're doing. If you're paving a road, you need a much stiffer material that can stand on its own. If you're doing a wall, the flow needs to be much more fluid.” And if you're pouring a patio, it needs to be somewhere in between.