Mechanical internal 'poker' vibrators¹ are the most commonly used, and the most versatile, of all vibration equipment. They can be powered by electricity, petrol engine or compressed air.

While their length is generally fixed at around a foot-and-a-half, the girth and cycle speed (vibrations per minute) varies.

Smaller sizes, say 20mm to 60mm diameter, are most commonly used for general purposes, and typically vibrate between 150 and 250 cycles per second.

Larger vibrators, up to say 180mm diameter, vibrate more slowly, say between 90 and 140 cycles per second, and are used for large-scale jobs. One of these will probably require two men to operate it, and for really big jobs (say six cubic metres plus), two can be operated in tandem to achieve 'melt down'.

Practical Tips

• The whole length of an internal vibrator should be immersed.

• Vibrators should be inserted vertically.

• Vibrators should not be allowed to touch the sides.

• Withdrawal should be undertaken slowly and carefully to ensure that all holes close up.

• Vibrators should only be used for compaction of wet concrete. They should not be used to move or transport concrete laterally.