Today most concrete is consolidated by vibration. Vibration subjects the fresh concrete to very rapid impulses which temporarily liquefy the mixture and cause the concrete level to subside. The entrapped air, being the lightest ingredient in the mix, rises to the surface where it escapes. Concrete may be vibrated externally by attaching a vibrator to the formwork, by means of vibrating screeds, and by vibrating tables. Internal or immersion vibrators are most commonly used in general construction. They are often called spuds or stingers. They are generally of the rotary type. A casing or head containing an unbalanced weight called the eccentric is immersed in the concrete. The eccentric is turned at high speed, causing the casing to revolve in a small orbit which subjects the concrete to vibratory impulses. Internal vibrators generally have the eccentric turned by electric motors, but they may also be powered by gasoline engines, compressed air or a hydraulic pump.

Of the electrically driven vibrators, the motor-in-head (MIH) type is probably the most common. Most MIH vibrators are high-cycle, which means that 180-cycle current is required for their operation. They use induction motors and operate in the concrete at a speed of about 10,000 revolutions per minute, which is only 5 to 10 percent less than the speed in air. Other types of vibrators include flexible shaft and compressed-air-powered vibrators.

The vibrator must effectively consolidate the concrete mixes used on the job. It should have an adequate radius of action (distance from the vibrator head over which the concrete is fully consolidated), and it should be capable of "melting down" and de-aerating the concrete quickly. Insofar as possible the vibrator should be reliable in operation, light in weight, easy to handle and manipulate, and resistant to wear. The effectiveness of a vibrator depends mainly on three things the head diameter, frequency, and amplitude or "kick."