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Concrete Vibrator

A concrete vibrator consolidates freshly placed concrete by transmitting high-frequency vibration into the mix, liquefying it momentarily so trapped air escapes and the material packs tight around reinforcement and into form corners. Proper vibration is what turns a placed load into dense, honeycomb-free structural concrete.

Models

31-58 mm on listed models

Head diameter

Brands

Cat classes

Pick a size class — capacity and reach differ across the range.

How it works

Internal (poker) vibrators — the dominant format in this class — spin an eccentric weight inside a steel head at the end of a flexible shaft, driven by an electric motor, gasoline engine or high-frequency converter. The operator inserts the head vertically into the fresh lift, lets entrapped air rise, and withdraws slowly, working a spaced pattern so vibrated zones overlap. Listed heads run 31-58 mm in diameter with protection hoses of 5.0 m; electric drive units span 42-250 V nominal and draw 1.4-20.0 A. Form-mounted external vibrators clamp to the formwork and vibrate through it where the mix is inaccessible, and surface vibration (screeds) consolidates thin slabs from the top.

Types & variants

Flexible-shaft poker vibrator: Motor or engine drives a flexible shaft with an eccentric head; the general-purpose internal vibrator for slabs, footings and walls.
High-frequency internal vibrator: Motor-in-head design fed by a frequency converter; consistent speed under load, common on structural and low-voltage-mandated sites.
Backpack vibrator: Engine carried on the operator's back driving a flex shaft — mobility for footings and remote placements without power.
External form vibrator: Clamps to formwork and vibrates through the form skin where congested reinforcement blocks internal access.

Key specifications

Specification	Typical range	What it means
Head diameter	31-58 mm on listed models	Smaller heads fit tight rebar and thin sections; larger heads move more concrete per insertion on mass pours.
Nominal voltage	42-250 V across listed electric units	Low-voltage units serve wet locations and sites mandating reduced-voltage tools; standard units need matching supply.
Nominal current	1.4-20.0 A	Draw must fit the circuit or generator feeding the unit, especially when several tools share supply.
Weight	5.3-30.0 lb on listed units	Carried weight drives operator fatigue across a full pour of repeated insertions.
Protection hose length	5.0 m listed	Sets the reach from drive unit to head, which determines how far the motor can sit from the placement.

How the industry sizes it

Internal vibrators are sized by head diameter against section thickness and reinforcement spacing: the head must pass between bars and suit the lift depth, with each insertion consolidating a radius roughly proportional to head size. Crews match head diameter to the thinnest congested section on the pour and increase insertion count rather than forcing an oversized head.

Applications

Consolidating slab-on-grade pours
Vibrating footings and foundation walls
Working concrete around dense rebar in columns and beams
Precast concrete production
Driveway and sidewalk placement
Consolidating tight formwork sections and corners

Safety & operation

Electric vibrators work in wet concrete by nature — ground-fault protection and intact cords are non-negotiable, and low-voltage systems exist specifically for wet-location safety.
Prolonged operation transmits hand-arm vibration; rotation among crew members and grip-friendly handling reduce cumulative exposure.
The spinning head must never contact the operator or run dry against formwork and rebar for extended periods, which overheats the head.

Standards & certifications

ACI · 309R: Guide to Consolidation of Concrete — insertion spacing, duration and withdrawal practice for internal vibration.
OSHA · 29 CFR 1926.404(b)(1): Ground-fault protection requirements for cord-connected tools on construction sites.
OSHA · 29 CFR 1926.702: Concrete and masonry equipment provisions applicable to powered placement tools.

Frequently asked

What head size suits a given pour?

Listed heads run 31-58 mm. The head must pass between reinforcing bars, so congested or thin sections take the small end and mass pours the large end, with insertion count adjusted accordingly.

What happens if concrete is under- or over-vibrated?

Under-vibration leaves honeycombing and entrapped air pockets; over-vibration segregates the mix, driving aggregate down and paste up. Correct practice inserts vertically, holds briefly, and withdraws slowly.

Why do some sites require low-voltage vibrators?

Operators stand in wet concrete holding an electric tool; reduced-voltage systems, down to 42 V among listed units, lower shock severity in that environment.

What is an external form vibrator for?

Where reinforcement is too congested for a poker head, external units clamp to the formwork and consolidate the mix through the form skin.