Vibrating screeds: levelling and compacting
A vibrating screed is an aluminium beam with a petrol engine and a centrifugal vibrator mounted at its centre. It is pulled across the top of the formwork to strike off surplus concrete to level and to vibrate it into place at the same time.
Beam length is the specification that matters. Too short and the operator chases the level in sections, which shows up as a wavy slab. Too long and the beam is unmanageable and sags in the middle. Choose a beam that spans your typical pour width with a small margin.
Power trowels: closing and finishing the surface
Power trowels come in three practical sizes. Small edge trowels with discs around 570 mm reach up to walls, columns and door openings. Walk-behind machines with a 1,000 mm disc handle the bulk of a slab. Ride-on machines with dual discs and working widths around 1,600 mm are for large-area production where finishing speed sets the programme.
Machine weight is a real selection criterion. Heavier walk-behind trowels with added ballast float wet concrete more aggressively, which matters when the mix is wet and the slab is thick. Lighter machines suit finishing passes and hire fleets where one operator moves the machine frequently.
Trowel blades wear and are replaced far more often than any other part. Confirm blade availability and price at the same time as the machine, and check that the blade mounting pattern is a standard one.
Scarifiers: preparing and removing the surface
A scarifier is a rotating drum of carbide cutters that planes the top of the concrete. It is used for surface preparation before coatings and overlays, for removing failed toppings, and for creating a mechanical key on a smooth slab.
Scarifiers are specified by milling width and depth per pass. Walk-behind machines around 250 mm wide are suited to smaller areas and edge work. Wider hydraulic machines from 350 mm to 500 mm cover large areas, and tracked remote-controlled versions keep the operator clear of dust and vibration on long runs.
- Milling width sets the number of passes needed to cover an area.
- Depth per pass sets how many passes are needed to reach a removal depth.
- Cutter count and condition drive the surface texture and the finish rate.
The order the machines are used
On a new slab the sequence is pouring, then striking off and compacting with the screed, then hand floats at the edges a trowel cannot reach, then power trowelling as the concrete sets. Scarifying is a later operation — on a new slab, before a coating or topping goes on.
- Vibrating screed — strike off and compact the wet concrete
- Hand float — open up and level margins and tight corners
- Edge trowel — finish alongside walls and openings
- Walk-behind or ride-on trowel — finish the open slab area
- Scarifier — prepare or remove the surface once cured
Choosing by the work you actually do
A contractor pouring small slabs and repairs needs an edge trowel or a mid-size walk-behind machine and a short screed beam. A slab contractor running large floor plates needs a ride-on trowel to keep up with the pour rate, plus a walk-behind machine for the margins.
Scarifying is a separate decision because it belongs to a different stage of the job. If you already own preparation equipment, the question is whether the machine you have is wide enough to keep up with the area, not whether you need one at all.
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