Laying Block Paving 4 to 6 cm Thick

The thickness of a paving block is about load, not looks. A thicker block is harder for a wheel to tip and spreads pressure into the ground better. A thin block under heavy point pressure is more likely to crack or tilt.

• 4 cm blocks are meant for foot traffic only: garden paths, patios, pool surrounds, the area under a bench or barbecue, the path to the compost heap.
• 6 cm blocks can also take pedestrian areas with occasional light vehicles, if the manufacturer states this for the product and the sub-base is built for it. A typical case is a path that a delivery van crosses now and then, or an area for bicycles and a ride-on mower.

Can you park on 6 cm paving? Manufacturers often allow it for an occasional car passing over, not for daily parking. What damages paving most is turning the steering wheel while the car is standing still. The tyre does not just press the blocks down, it pushes them sideways and breaks their edges. For a driveway, a parking space or anywhere a car turns, 8 cm blocks are the right choice.

If you expect to turn part of the area into a parking space one day, decide now. Swapping thin paving for thicker blocks later means lifting the whole area, digging deeper and compacting the sub-base again.

At first glance the two thicknesses look the same, and many block shapes are made in both. On site, however, the difference is clear:

• Load: 4 to 6 cm is for pedestrians and the odd light vehicle. 8 to 10 cm belongs on driveways, car parks and areas used by vans or bin lorries.
• Sub-base: under thinner paving a thinner layer of crushed stone and a shallower dig are usually enough. Less soil goes out, less aggregate comes in.
• Compaction: thin blocks need a lighter plate compactor with a rubber mat. A heavy plate suitable for 8 cm blocks can crack 4 cm ones.
• Edging: pedestrian areas usually get garden edging kerbs. Areas for vehicles need heavier kerbs set deeper in concrete.
• Handling: thin blocks are lighter. They can be carried by hand or wheeled through a garden where machinery cannot reach.
• Cutting: a thinner block cuts faster with a smaller saw. Narrow offcuts, though, are more fragile and work loose more easily.

On many properties the two thicknesses are combined: an 8 cm driveway with a 4 or 6 cm path to the door and patio. The sub-base makes up the difference in height, so the surfaces can run on smoothly. The transition is worth separating with a kerb or a row of blocks set in concrete, so the thinner paving does not creep at the edge of the driveway.

Levels, falls and drainage

Before any digging, it must be clear where the finished surface will sit and where the water will go. Paving next to the house must fall away from it, usually by roughly 1.5 to 2 %. On a path 2 m wide that is about 3 to 4 cm. On a patio the level is set from the door threshold, at an entrance from the step. If water cannot run off into the lawn, plan a channel drain or a soakaway in advance.

Services under the area

Before digging, have the underground services located and marked: water, drainage, gas, electricity and telecoms. Utility companies or a local "call before you dig" service will do this on request. If a gas pipe is damaged during digging or you smell gas, leave the area, do not use flames or switches, and call 112 or the local gas emergency line.

Access, storage and materials

Prepare space for pallets, aggregate and waste. If the area can only be reached through a yard or garden, say so in advance, because it changes how the work is done. Order all the paving at once, from one production batch, with spare blocks for cuts and future repairs.

Permission and consent

Paths and patios at a private house are usually straightforward, but local building regulations differ. Some areas have rules on paving front gardens or on where surface water may drain. Check with your local building authority rather than relying on what neighbours did years ago. In a block of flats, any change to shared outdoor areas is decided by the owners' association or building management.

Coordinating with other trades

Everything that goes under the paving must be finished before the sub-base: rainwater drains, service connections, ducts for garden lighting, irrigation. Wiring for lights and outdoor sockets may only be connected by a qualified electrician. The plinth of the house and the damp-proofing along the wall should be complete before paving is laid against them. Planting and turfing are sensibly left until after the paving, so machinery does not ruin finished beds.

Excavation and formation

The depth of the dig is the sum of the block thickness, the bedding layer and the sub-base. For a pedestrian area this is usually around 25 to 30 cm below the finished surface. The bottom of the dig, called the formation, is shaped to the fall and compacted. On clay soil that turns to mud when wet, a geotextile membrane is laid on the formation so the stone is not pushed into the soil.

Sub-base

The sub-base is graded crushed stone, typically 0/32 or 0/63. For a pedestrian area it is usually about 15 to 20 cm thick. For 6 cm paving with occasional vehicles it is made thicker, around 20 to 25 cm. It is compacted in layers of roughly 10 cm, and the stone should be slightly damp. Dry stone compacts poorly, while soaked stone ripples. The sub-base decides whether the area lasts. Neither the bedding nor the blocks can make up for badly compacted stone.

Edging

Edging kerbs are set before the blocks are laid, in concrete with a haunch on the outer side. They hold the area together: without them the outer blocks spread over time. The concrete should set for at least a few days before the paving is compacted. The exact time depends on the weather.

Bedding layer

A layer of fine grit, for example 2/4 or 4/8, is spread over the sub-base and is about 3 to 4 cm thick after compaction. It is screeded with a straightedge running on guide rails set to the fall. Nobody walks on the screeded bedding. A thicker bedding layer is no substitute for a proper sub-base, because it settles unevenly over time.

Laying and cutting

Blocks are laid working forwards from paving already in place, so nobody steps on the bedding. Blocks are taken from several pallets in turn, otherwise patches of colour appear. The joint is usually 3 to 5 mm, and many blocks have spacer nibs that keep it. Lines are checked with a string line. Cuts at kerbs, manholes and walls are made with a wet saw or an angle grinder. With thin paving, avoid narrow slivers. A piece smaller than roughly a third of a block works loose and cracks easily, so it is better to split the cut over two neighbouring blocks.

Jointing and compaction

Dry 0/2 sand or fine grit, as recommended by the manufacturer, is brushed into the joints. The area is then compacted with a plate compactor fitted with a rubber or polyurethane mat, working from the edges towards the middle in overlapping passes. A lighter plate is used for 4 cm blocks. After compaction the joints are topped up and the area is compacted again. The sand keeps settling for several weeks, so the joints need topping up after a while.

Shape and pattern

Pedestrian areas use square blocks, rectangles, interlocking I-shapes and larger formats. A herringbone or staggered bond spreads load better than blocks laid in straight rows, and with thin paving this matters even more. Large-format units 4 cm thick look elegant but are more sensitive to an uneven base and crack more easily if driven over. They belong only on footpaths and patios.

Surface

Plain blocks with no surface treatment are simple and hard-wearing. Blocks with a face layer have a finer surface and more stable colour. Shot-blasted, ground or split surfaces resemble natural stone. For a patio or pool surround, think about slip resistance in the wet and how easy the surface is to clean. Smooth dark paving gets very hot in summer, which you will notice walking barefoot.

Bedding and joints

Grit in the bedding lets water through and washes out less than sand, which is why it is now more common. Polymeric jointing compounds make it harder for weeds to grow and for joints to wash out. According to the manufacturers, though, they usually need a permeable base, a certain joint width and dry weather during application. If water under the paving has nowhere to go, the compound can break up.

Edging

Concrete garden edging kerbs are common and sturdy. For curved garden paths, steel or plastic edging strips that can be bent are sometimes used. Whatever the edging, it must support the edge firmly, otherwise the outer blocks drift into the lawn.

The amount of work per square metre can vary a great deal between two areas. The job is easier with:

• A plain rectangular shape with no obstacles
• Good access for a mini loader and aggregate delivered right to the area
• Firm, free-draining soil
• A simple pattern in one colour

The job is harder with:

• Curves, cut-outs, manholes, gullies and posts that mean many cuts
• A narrow path where laying cannot get into a rhythm and the share of cuts is high
• Soil and stone carried by hand through the garden
• Breaking out old concrete or paving and taking away the rubble
• Slopes, steps and level changes at thresholds and plinths
• Clay or waterlogged soil that needs a membrane and a thicker sub-base
• Mixed colours and decorative patterns

A small garden path is usually finished in one or two days. A patio of around 30 m² typically takes two to four days, much of it spent on excavation and sub-base. The paving does not need to dry: once compacted, you can walk on it straight away. The only wait is for the concrete under the edging. Rain stops the work when compacting the bedding and when jointing, because wet sand will not run into the joints.

• Weak or poorly compacted sub-base: after the first winter, dips and waves appear and water stands in them.
• Bedding layer too thick: the paving settles unevenly, especially along the routes people walk.
• Fall towards the house or no fall at all: water runs to the plinth, the wall gets damp and ice forms at the door in winter.
• Missing or poorly set edging: edges spread, joints open and blocks tip.
• Blocks laid tight with no joints: edges chip off during compaction and with temperature changes.
• Compacting without a mat or with too heavy a plate: scuffs and marks stay on the surface and thin blocks crack.
• Parking on 4 cm paving: blocks crack and tilt, and the repair means lifting the area and building a new sub-base.
• Laying one pallet after another: the area shows visible bands of colour.
• Joints not filled: blocks do not lock together, move underfoot and weeds grow faster.

A white bloom on new paving is usually efflorescence. It is a natural effect in concrete, generally disappears by itself within a few months and is not a defect to complain about.

A capable amateur can manage a pedestrian area in 4 to 6 cm blocks. You can hire a plate compactor with a rubber mat from a tool hire shop. A patio that meets a door threshold, or paving against a plinth with damp-proofing, is better left to professionals, because mistakes in level and fall are hard to put right there.

1. Have underground services located and marked on site.
2. Set out the area with pegs and string, and fix the finished level and the fall away from the house.
3. Dig out the soil to the required depth and compact the formation to the fall.
4. Lay a geotextile membrane with overlaps on clay soil.
5. Bring in the crushed stone in layers of roughly 10 cm and compact each layer.
6. Set the edging in concrete along the string line and let the concrete harden.
7. Lay guide rails to the fall, spread the grit and screed the bedding with a straightedge.
8. Remove the rails, then carefully fill and smooth the grooves.
9. Lay the blocks working forwards from the finished area, taking from several pallets in turn and keeping the joint the manufacturer specifies.
10. Check the lines with string as you go and adjust gently with a rubber mallet.
11. Cut edge pieces with a wet saw, wearing eye, ear and respiratory protection.
12. Brush dry sand or fine grit into the joints.
13. Compact the area with a plate compactor fitted with a rubber mat, from the edges towards the middle.
14. Top up the joints, sweep off the surplus and top them up again after a few weeks.

At handover, walk the area slowly and carefully. A 2 m straightedge shows unevenness. A watering can shows where water really goes. As you walk, notice whether any block moves or rocks. Check in particular:

• The fall runs away from the house and water does not stand anywhere
• There are no noticeable dips or humps under the straightedge
• The level at thresholds, steps and the plinth matches what was agreed
• The edging is firm, in line and backed with concrete
• Joints are even and full
• No block moves underfoot
• There are no cracks, chipped edges or compactor scuffs
• Colour shades are spread evenly with no bands
• Cuts at manholes and edging are clean, with no small slivers
• Covers and gullies sit flush with the paving
• Spare blocks from the same batch are left for future repairs
• The surroundings are tidy and waste has been removed