What Is a Poker Vibrator? Internal Concrete Vibrators Explained

What a poker vibrator is

When fresh concrete is placed, it holds a surprising amount of trapped air — often 5 to 20 percent by volume. Left in the mix, that air sets as voids and honeycombing: weak spots that cut strength, let water and chlorides reach the reinforcement, and shorten the life of the structure. An internal vibrator is the tool that removes it. A vibrating steel head — usually called the poker or bottle — sits on the end of a flexible hose and is plunged straight into the pour, so the vibration works from within the concrete rather than from the surface. Depending on region and trade you will hear it called a poker vibrator, internal vibrator, immersion vibrator or needle vibrator; in other markets the same tool is a buława wibracyjna, a trilnaald or a Rüttelflasche. They all describe the same device. Lievers Holland has designed and built this kind of concrete compaction machinery in Mijdrecht, the Netherlands, since 1954.

How a poker vibrator works

Inside the steel head, an eccentric weight or pendulum spins at high speed and strikes the inner wall of the bottle, making the whole head oscillate rapidly. A typical site poker runs at around 12,000 vibrations per minute — the Lievers P18Li, for example, vibrates at about 12,000 vpm through interchangeable 28, 38 and 45 mm heads. That energy passes straight into the surrounding concrete and briefly liquefies it, so the trapped air rises to the surface and escapes while the cement paste flows fully around the reinforcement and into the corners of the formwork. The concrete is consolidated when the large air bubbles stop rising, a thin film of paste glazes the surface around the head, and the note of the vibrator steadies. The head is then withdrawn slowly so the concrete closes behind it, and the operator moves to the next insertion point. Each insertion consolidates a roughly circular zone, so points are spaced to overlap — commonly about 50 cm apart for a typical site poker.

The main types of poker vibrator

Poker vibrators are grouped mainly by how the head is driven:

• Cordless battery pokers. A rechargeable battery drives a small electric motor in the handle, which spins the flexible drive shaft that runs the head. Because there is no cable or converter, these tools shine on sites without mains power and on small, scattered pours. The Lievers P18Li is an 18 V lithium-ion example weighing about 2.35 kg with the battery fitted.
• Electric high-frequency pokers. These reach the higher frequencies that give fine, even compaction. Some run through a separate frequency converter or transformer; others, like the Lievers LHF-E, use an integrated inverter that converts a standard single-phase supply into the high-frequency output the motor needs, so no external converter is required on site.
• Pneumatic pokers. Driven by compressed air rather than electricity, these are chosen where an air supply is already on site or where an air-driven tool is preferred for the working environment.

Within each type, different head sizes and hose lengths let you match the tool to the element being poured.

Head diameter and what it affects

The diameter of the poker head is the main sizing decision. Common heads span roughly 25 to 65 mm, and the choice is a trade-off. A smaller head — around 28 mm — fits into thin sections, heavily reinforced elements and precast moulds where access is tight, but consolidates a narrower zone per insertion. A larger head — 45 mm and up — moves far more concrete per insertion and suits mass pours, foundations and thick walls, at the cost of extra weight and more vibration reaching the operator's hands. Head diameter also sets the compaction radius: across the Lievers high-frequency range the consolidated zone runs from about 45 cm for the smallest head up to about 85 cm for the largest, which is what determines sensible insertion spacing. Bigger is not automatically better — the right head is the one that reaches the concrete and delivers enough energy without being unwieldy.

When to use a poker vibrator — and when not to

A poker vibrator is the tool for consolidating concrete in depth: walls, columns, foundations, beams, thick slabs and most structural elements where the mix has to flow around dense reinforcement. Because it works from inside the pour, it reaches consolidation that surface methods cannot. Surface tools — such as a vibrating screed or beam — work only the top layer of a slab to compact and level it; on a floor pour the two are used together, with the poker consolidating the full depth and the screed finishing the surface. There is one important exception: self-compacting concrete (SCC) is engineered to flow and release air under its own weight, and it must not be vibrated with a poker, as that would cause segregation. For ordinary structural concrete, though, an internal poker vibrator remains the most reliable way to reach full strength and durability.