A concrete slump test is used to determine the correct water content in a batch of concrete. “Slump” is the distance, measured in inches, the concrete settles after the slump cone is removed. A concrete batch with high slump is an indication that the concrete has to much water in it and will likely be weak when fully cured. The ideal mix will not be too stiff or too soft, but will have a slump of about 4″. If you’re working in very hot or dry conditions, or if the mold has intricate shapes, you may want a slightly wetter mix. Keep in mind that the more water in the mix, the higher the risk of cracks. A mix that is too dry is hard to pour and vibrate.
Performing a concrete slump test will help give you an idea of what the right mix should feel like. Over time you’ll develop a feel for it, but in the beginning it helps to keep track of the amount of water you add so you can reproduce the same results throughout projects.