A vibrating poker compacts wet concrete, forces air out, and ensures the mix fully surrounds mesh, rebar, and pipes. Skip it, and you risk honeycombing, voids, and structural failure — especially on deeper or reinforced slabs. This guide explains how to use a vibrating poker in a concrete slab correctly, when to insert it, how long for, and why timing matters as much as technique.
For domestic slabs (100–150mm), a 25–45mm head is usually enough. For deeper slabs, pads, or trench pours, you may need 50mm+. Most pokers run on electric or petrol power. Check your access to power, and make sure the shaft is long enough to reach the full depth of your slab. A poker that’s too large or small won’t vibrate efficiently — or may cause over-compaction at the surface.
Don’t start vibrating too early — wait until the slab section is poured and loosely levelled (raked or roughly screeded). This gives you room to insert the poker vertically and work it cleanly. Never vibrate dry or compacted mix — the concrete must still be fresh, workable, and able to move when agitated. Work in sections as you pour, rather than waiting to do the whole slab at once.
Push the poker in vertically — not on an angle — to avoid disturbing rebar, mesh, or formwork. Let the weight of the poker drop it through the mix, don’t jam it. Insert it deep enough to reach the full slab depth, and if you’re layering over a previous pour, push 75–100mm into the layer below to bond and avoid cold joints. On thin slabs, insert carefully to avoid hitting the base or insulation.
Once inserted, hold the poker steady in each position for 5–15 seconds depending on mix slump, slab depth, and vibration strength. You should see air bubbles rise and the surface flatten slightly. That’s how you know compaction is working. Overdoing it can cause segregation — where aggregate settles and water rises — so always watch the reaction. Once bubbles stop or the surface stops shifting, withdraw slowly.
When removing the poker, lift it out slowly at about 3–5cm per second. Pulling too fast creates holes or gaps — especially near pipes, corners, or mesh. On vertical edges or against formwork, be extra careful. Some pros use a slight wiggle on withdrawal to collapse any narrow air paths. Once out, move laterally about one poker width (300–400mm) and repeat across the slab.
Once a section is fully vibrated, let it settle for a minute before screeding or bull floating. You should see a flat, slightly glossy surface with no holes or trapped air. If it’s lumpy or collapsed in places, re-vibrate with care — but don’t overwork. Screed gently from the edges, and avoid standing where you’ve just vibrated. Proper poker use leaves the slab dense, level, and ready to finish.
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