Paving Screed Bars and Levelling Systems

What a screed bar does in paving work

A screed bar, also called a levelling or profiling bar, is used to level the sand-cement or aggregate bedding before paving blocks are laid. The principle is simple: two rails are set on the prepared base at a given height, material is spread between them, and the bar is drawn along the rails. Surplus aggregate is struck off, leaving a layer of exactly the same thickness along the whole run.

Typical bedding thickness under block paving is 3–5 cm and has to be held to a tolerance of a few millimetres. The deviation is not cosmetic: a block laid on too thick a layer will settle lower than its neighbours after compaction, and one on too thin a layer will stand higher. Running a plate compactor over it will not fix this — compaction locks in whatever the levelling stage produced. Even bedding is therefore a condition of even paving, not an optional refinement.

A screed bar is a purely paving tool and should not be confused with a vibratory screed, which compacts and finishes fresh concrete — those are in vibratory screeds.

Types of bedding levelling system

The distinction follows the scale of the job: the larger the area, the more a wide, telescopic system pays off.

TELEPLAN telescopic screeds have an adjustable width — the TP-100/165 works across 1,000–1,650 mm at a weight of 4.6 kg, while the larger TP-150/260 and TP-200/350 cover 1.5–2.6 m and 2–3.5 m respectively. One tool therefore handles runs of different widths without carrying several fixed bars. The TAS-UNI systems are stationary structures weighing 85 kg, set up across a wide working front.

Choosing a screed bar

The first criterion is the width of the run you want to level in one pass. A 1.5 m pavement is covered by the TP-100/165 or TP-150/260; a 3 m driveway by the TP-200/350; a yard or car park by a TAS-UNI system reaching 4.5 or 6 m. The wider the reach, the less rail repositioning — but also the heavier the equipment and the greater the need for two operators.

The second criterion is how levels are set. On small areas, rails placed at a given height and checked with a spirit level are enough. On larger ones, levels and falls are set with a laser level, and the bar merely reproduces the established plane. On driveways and yards a fall is mandatory: typically 1.5–2% towards the drainage point, meaning 1.5–2 cm per metre of length.

The third point is accessories. AZL levelling rails hold a constant height along the full run, and the AW-120 aluminium square with 1200 × 1200 mm arms lets you check right angles at corners and edges — an overlooked detail that decides whether courses of blocks start drifting out of line.

Frequently asked questions — screed bars and bedding preparation

What is a screed bar for block paving used for?

A screed bar levels the bedding before blocks are laid: drawn along two rails, it strikes off surplus aggregate and leaves a layer of uniform thickness, typically 3–5 cm. Every block then seats at the same level. This operation determines how flat the finished surface will be — an error in the bedding cannot be fixed by later compaction, because a plate compactor locks in the shape of the layer rather than correcting it.

How thick should the bedding under block paving be?

Standard sand-cement or aggregate bedding under block paving is 3–5 cm thick after compaction, held to a tolerance of a few millimetres across the whole area. A thicker layer causes uneven settlement after compaction; a thinner one leaves no room to adjust the height of individual blocks during laying. The bedding does not replace the sub-base — it sits on a load-bearing aggregate layer of far greater thickness, sized to the loading the surface will carry.

How does a screed bar differ from a vibratory screed?

A screed bar is an unpowered paving tool — it levels dry bedding under blocks by striking off surplus material. A vibratory screed is a powered machine that compacts and finishes freshly poured concrete by vibrating it. Both have a long profile and both level, but they work on different materials at different stages of construction.

What width of screed bar should I choose?

Width is matched to the run levelled in a single pass. Pavements and perimeter strips 0.6–1.6 m wide are served by the telescopic TP-60/100 or TP-100/165 weighing from 4.6 kg. Patios and paths call for the TP-150/260, driveways up to 3.5 m for the TP-200/350. Yards and car parks over 3.5 m use TAS-UNI systems with a working width of 450 or 600 cm, which weigh around 85 kg and need two operators.

What fall should a block-paved surface have?

Block paving requires a fall to shed water, typically 1.5–2%, which is 1.5–2 cm per metre of length, directed away from the building towards drainage or a planted area. The fall is set while levelling the bedding, by placing the rails at correspondingly varying heights — most often with a laser level. A surface without a fall leads to standing water, and in winter to frost damage to the joints and sub-base.

Do I need a laser level to level the bedding?

On small areas — perimeter strips, paths, modest patios — rails set at a given height and checked with a spirit level and string line are enough. On driveways, yards and car parks, levels and falls are set with a laser level and the bar simply reproduces the established plane. The larger the area, the faster errors accumulate when transferring levels by hand, so beyond a few hundred square metres a laser stops being a convenience and becomes a condition of repeatability.

Can a screed bar be used on aggregate and crushed stone?

A screed bar works on fine loose materials — sand, sand-cement mix and the grit used as bedding. Spreading and initial profiling of thicker crushed-stone sub-base layers is instead done with spreading machines such as the PowerPlan, because large aggregate fractions jam under the bar's profile. Bedding for block paving is always laid on a previously compacted sub-base, never directly on natural ground.