SIMAQ School · Course

Concrete vibration

Honeycombing doesn't appear when you strip the forms. It appears on pour day, between one insertion and the next.

The fundamental

Ten times the head

A vibrator head consolidates a circle of roughly ten times its diameter. A 38 mm head reaches about 38 cm. That number decides everything else.

Concrete between insertions never got vibrated. Air and mortar-starved gravel stay there: classic honeycombing, invisible until stripping.

Circles overlap and leave no dead zone. It's the only way to guarantee the whole element was consolidated, not just the entry points.

No structural harm, but you waste time redoing done work — and on a pour, time is set.

The largest head that passes freely between bars is the one that performs. Tell us your element and your rebar.

What are you pouring?

Element thickness15 cmClear gap between bars12 cmMeasure it at the tightest mesh: the head must pass without touching steel.

Your vibrator

SQ28 PRO

Petrol, long hose · 5.5 HP · 6 m hose

In slabs you don't dip point by point: drag the head almost horizontally, with passes the same 30 cm apart.

The technique

1
Plunge fast
One movement to the bottom of the lift. Going down slowly pushes air downward instead of letting it escape.
2
Hold still
A few seconds, until the concrete stops settling and a thin sheen of paste appears. That's when the air is out.
3
Withdraw slowly
3 to 5 cm per second. Yanking it out opens a channel the concrete can't close: an air tube left inside the element.

When pouring over a previous lift, sink the head ~10 cm into it while it's still plastic: the two knit into one piece with no hidden cold joint.

Using the vibrator to move concrete
Dragging it sideways to spread the mix separates gravel from mortar. Place concrete with a shovel; the vibrator only consolidates.
Touching the rebar
A vibrating bar loses bond with the concrete around it, then telegraphs or cracks at the surface. Keep the head clear.
Hitting the formwork
Closer than 10 cm to the mould, grout leaks through the joints and leaves stains and porosity on the exposed face.
Running it in the air
The vibrator is cooled by fresh concrete. In air it overheats, shortening head and hose life.
Over-vibrating
Going too far segregates the mix: gravel sinks, water rises. You get a milky surface and a weak layer right at the top.

The vibrators