Paving units of concrete, clay, brick, timber, stone or tile are popular and attractive options, though it’s essential they are installed correctly and designed to manage run-off and permeability requirements
The following is the second of a three-part guide on how pavers should be best installed and managed.
Pavers
Pavers are manufactured in a range of shapes, colours and materials. Pavers can be shaped so that they interlock when installed or are close butted and restrained by an edging. They are suitable for both pedestrian and vehicle traffic, depending on the paver type and the sub-base preparation.
Most pavers are manufactured from concrete or fired clay, although wood-block pavers have been common in European cities.
Clay pavers are usually square or rectangular. Their colour is determined by the clay they are manufactured from and the firing temperatures.
Concrete pavers can be produced in a range of colours and in a very wide range of shapes, surface finishes and thicknesses. Options range from large precast flagstones (500mm or 600mm square) to smaller (150–200mm) shaped, square or rectangular units. They range from partially or fully interlocking paving units through to units designed to allow grass to grow through them while still providing a solid surface.
Concrete paving can be finished with a number of surface finishes – smooth faced, honed, shot blasted, exposed aggregate, sand blasted or acid etched – each offers different aesthetic properties and differing slip properties.
Concrete pavers should be manufactured in accordance with NZS 3116 or AS/NZS 4456. Concrete pavers are produced in a variety of ways, and the quality varies with the method of production. In general, pavers with higher technical properties such as strength, resistance to abrasion, colour retention and dimensional correctness are produced using a hydraulic press. The more common method of wet casting (where concrete is poured into moulds) produces pavers that are generally prone to greater variation in size and quality but may be more dense in the top surface.
Pavers can be manufactured with bullnose edge profiles for steps and pool surrounds.
Also used as paving are:
Old bricks – these can be uneven in size and profile, slippery, relatively soft and are not suited to vehicle traffic or heavy pedestrian use.
Stone setts, cobbles or blocks.
Hardwood blocks (or treated timber blocks or sleepers).
Accessories
Accessories to complete paving work include:
Flexible PVC or aluminium concealed-edge restraints.
Interlocking precast kerbs, including radiused units in a number of styles designed for specific uses.
Mountable precast kerbs (with one sloping edge).
Bullnosed pavers for steps, edging and cappings.
Paver shapes
Common forms of paving units can be non-interlocking, interlocking in one direction or fully interlocking. The interlocking action improves the overall strength and in-service performance of the paving by dissipating loads across the paving area.
Pavers are available in a range of thicknesses (typically 40-80mm) to suit the expected loads (light pedestrian, heavy pedestrian, light vehicle or heavy vehicle).
A range of laying options is available. Laying patterns for fully interlocking paving are limited to herringbone, basketweave and stretcher bond patterns, while semi-interlocking pavers can be laid in herringbone and stretcher bond patterns only. Herringbone is the preferred pattern for trafficable areas (laid diagonally at 45° to the direction of traffic).
Other components
Pavers are the visible finished product, but equally important are the unseen components, which include:
Edging – for example, timber, steel, plastic.
Concrete to bed edge pavers into, called haunching.
Base course of graded granular material, free of organic matter.
Bedding sand – clean, well graded sand with a particle size between 0.75-4.75mm.
Crusher fines for bedding pavers into.
Joint sand – fine dry plaster sand with angular particles (2mm maximum particle size), also available with cement content for permanence and to minimise weed growth
Planning work
When planning paving design and construction, consider:
Minimising areas of hard-paved surfaces.
Unless subsoil conditions prevent reasonable percolation, trying to provide drainage from impervious paving to permeable surfaces at edges rather than to stormwater drains.
The dimensions and layout of the paving – paving units are modular, and tailoring dimensions of the area to be paved at the design stage will minimise the need for cutting pavers and will improve overall appearance and performance.
Avoiding cutting pavers into less than one-third of their width – where cutting is unavoidable, insert the cut portions into the pattern to avoid having them at the end of a row.
The space available for excavation, storing materials and carrying out the work – will there be sufficient space or will materials have to be stored elsewhere and carried in as required?
Access for equipment.
How falls for drainage will be incorporated and the placement of drainage points – falls are typically 20-30mm per metre to allow for efficient run-off (2-3%).
The detailing and construction to be used at changes in level.
The edging detail – some options can result in inconspicuous edges.
The use of colour to define edges or create patterns – when creating patterns in areas subject to vehicle traffic, interlocking pavers will hold the pattern as they are better able to resist the turning forces generated by vehicles, especially in areas where cars back and turn hard, such as exiting from a garage or car park.
The use of other surfaces in conjunction with the paving and the detailing of the junctions between the two materials.
Cutting of pavers will be required where:
Interlocking pavers or pavers that are not square or rectangular are used.
There are curves or angles in the paved area.
Herringbone, stretcher bond or some other laying patterns are used.
Excavation and hardfill
The key to good paver performance is the preparation of the base to provide a sound, even footing for the pavers to be laid over. Inadequate preparation may end in expensive remedial work.
Excavation of the paved area must include removal of topsoil and all organic matter. The depth to be excavated will depend on paver thickness, hardfill and sand depths and the intended use of the paving.
The bearing capacity of the soil under the paving can be indicated by a heel test carried out after the initial excavation has begun:
Weak – walking leaves a very noticeable sunken footprint.
Medium – a footprint is left with a small amount of soil compression.
Strong – no impression is left in the soil.
Areas of soft ground must be removed down to solid bearing and the resulting excavation filled with compacted hardfill. If not remedied, areas of soft ground will show in the completed paving as a hollow or settlement.
When excavating:
Remove excavated material clear of the work area.
Form falls in the excavated base.
Finish the surface to +0 or -20mm.
When placing hardfill:
Compact the material in 100mm (maximum) layers – for small works, use a plate compactor or a hand-pulled roller.
Finish the surface to +0 or -10mm.
Edge restraint
All paving requires some form of edge restraint to hold the pavers in place. Options are:
Square or rectangular pavers set into a concrete haunch.
Concealed flexible PVC paving edge for paving 40-80mm thick.
Kerbing – precast concrete, stone blocks or cast in situ concrete.
H4-treated timber (or durable hardwoods) securely pegged.
Stone blocks.
Stone blocks, precast kerbing, pavers and other unitary edge units all require setting into a concrete haunch to accurately locate and hold them in place.
Bedding material (sand/crusher fines)
Sand or crusher fines are the beddings that the pavers are laid directly onto. The bedding supports the pavers but will not mask irregularities in the hardfill if it does not meet the required tolerances.
The bed should be 20-30mm thick when compacted (allow 5-10mm for compaction) and damp but not wet.
When laying, allow additional thickness for compaction and screeding to level. Limit the area of prepared bedding to a size that will be paved over in a single work session. Jointing sand or joint-filling sand is specially produced to lock pavers into place. Some proprietary products are suitable for paving on sloping ground, areas of high wind or areas that are regularly swept (including by mechanical sweepers). Even after curing, these products typically still allow slight movement of the pavers. Some have additives that inhibit weed growth or insect infestation. If choosing a branded product, ensure it does not produce leachates.
Laying pavers
Good practice when laying pavers:
Start from the straightest convenient edge.
Always work uphill on slopes.
Maintain the manufacturer’s recommended joint width – typically 3mm.
Regularly check the laying pattern for alignment/squareness and accuracy.
Compact the pavers into the bedding sand (carry out a test on a small area to gauge the required sand depth before compacting). Compaction using a plate compactor is recommended, but for small areas, use a rubber mallet or hammer and a short thick piece of timber.
Cut pavers to fit as work proceeds. Recommended cutting methods are a concrete saw or paving splitter as they give more accurate cutting, but for small jobs, a bolster chisel may be used.
After laying, sweep dry sand into all joints then revibrate the area, repeating the process until all joints are filled.
Keep vehicles off the paved area until all work is complete.
Use a running board when transporting materials across the unfinished paving in a wheelbarrow.
This article was first published in BRANZ’s Landscape Construction book, Second Edition and is reproduced with permission.
The book covers the design, building and planning rules as they apply to landscape construction and provides guidance on design and construction to ensure good practices are followed. It can be purchased at www.branz.co.nz.