Concreting

The choice is decided by the geometry of the element. An internal vibrator (a 25–65 mm poker) is immersed in the mix and suits elements thicker than 15 cm — foundations, footings, walls and columns. An external vibrator is bolted to the formwork and compacts through the wall of the mould, so it fits precast units and thin-walled, densely reinforced elements. A vibrating screed compacts and levels slabs and floors up to about 15–20 cm thick at the same time, using a 2–4 m beam.

An internal vibrator works from inside the mix: a poker 25–65 mm in diameter is immersed every 30–50 cm for 5–15 seconds, and the vibrations (12,000–18,000 per minute) drive air out of the cross-section. An external vibrator is bolted to the formwork and transmits the vibrations through the wall of the mould. A poker is used for massive elements accessible from above; an external vibrator suits thin, heavily reinforced or precast elements where the head cannot be inserted.

A vibrating screed and a power trowel work at two different stages. The screed is run over the fresh mix immediately after it is spread — a 2–4 m beam compacts the top layer and strikes the slab off to level. A power trowel (a machine with rotating blades or a 600–1,200 mm disc) is only started after initial set, when a foot leaves a mark of about 3–5 mm; it smooths and hardens the surface. The order is fixed: screed, set, then troweling. For levelling choose vibrating screeds, and for finishing the concrete troweling range.

For massive foundations and footings the best choice is a 50–65 mm poker with a large radius of action (up to 50–70 cm), which quickly compacts big volumes. For columns and walls a 40–50 mm poker works well, and for dense reinforcement and thin elements a slim 25–38 mm head. A thin slab up to about 15–20 cm is compacted mainly with a vibrating screed, assisted by a 25 mm poker along the edges. In thin-walled and precast elements where a poker will not fit, external vibrators fixed to the mould are used.

The poker diameter is matched to the bar spacing and the volume of concrete. Heads of 25–38 mm slip between closely spaced bars and suit columns, ring beams and thin elements; 40–50 mm pokers are the all-round choice for walls and floors; 50–65 mm is reserved for footings and massive foundations. A poker that is too large will not reach the bottom in dense reinforcement — in that case an external vibrator performs better.

Vibrating removes air bubbles from the mix that can make up 5–20% of the volume in uncompacted concrete. Every 1% of trapped air lowers compressive strength by about 5–6%, so compaction genuinely increases the load-bearing capacity and density of the element. Vibrating eliminates honeycombing and voids and improves the bond between concrete and reinforcement. Standard EN 206 requires the mix to be fully compacted. Over-vibrating that causes aggregate segregation is just as harmful as under-vibrating, which is why the vibration time at a single point is limited to a few to a dozen or so seconds.

The alternative to a poker is other mechanical methods, not giving up compaction. Slabs and floors up to about 15–20 cm thick are effectively compacted by a vibrating screed; thin-walled elements and precast units by an external vibrator bolted to the formwork; and self-compacting concrete (SCC) flows without vibration thanks to admixtures. Manual rodding with a bar only works for very small volumes. For typical structural elements a 25–65 mm poker remains the most effective, and under-compacted concrete can lose as much as 30% of its strength.

A frequency converter turns the standard 50 Hz mains supply into a high-frequency current of around 200 Hz, which high-frequency vibrators with the motor built into the poker require. Without it, such heads will not reach the full 12,000 vibrations per minute or full compaction power. Models from the range, such as the Enar BOXEL 215, 225 and 325 or the Husqvarna CF25M (230 V) and CF25T (400 V), power one or several pokers at once and protect the motor against overload. The choice depends on the number of pokers and the supply — single-phase 230 V or three-phase 400 V.

Prices depend on the type and output of the equipment. Light electric pokers start on the market at a few hundred euros, while complete high-frequency vibrators with a converter cost from around €500 to a dozen or so thousand euros. Single-disc walk-behind power trowels usually fall in the range of a few to a dozen or so thousand euros, and ride-on twin-rotor machines cost tens of thousands. We give the current prices of all items in the department on the individual product pages, and orders are fulfilled online.

The concreting department carries equipment from leading manufacturers. The largest share of the range is Enar — a specialist in internal vibrators and converters — and Wacker Neuson, known for internal and external vibrators. They are complemented by Altrad Belle, plus Beton Trowel in tools and power trowels, Norton Clipper, and Husqvarna Construction in external vibrators and screeds. You will find the individual equipment types in the five subcategories of the concreting department.