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How to lay a patio

Lay a patio

Concrete paving slabs are an attractive and practical choice for a front garden.

It is important to remember that any large area of paving needs a firm base.

Tools and materials

Builders tools

Quantity: Optional

Timber

Quantity: 1

Rubber mallet

Quantity: 1

Concrete and mortar

Quantity: Optional

Sharp sand

Quantity: Optional

Angle grinder

Quantity: 1

Spade

Quantity: 1

Hardcore

Quantity: Optional

Useful videos

Related How to guides

Buying guides

Paving calculator.
Use this handy calculator to work out how many paving tiles you require.

Ideal for the job

Marking This nylon builder’s line attached to hammer-in pins is an invaluable tool when setting out new paving, or for any kind of garden construction work.

Cutting An angle grinder is perfect for cutting stone, paving blocks and slabs. Make sure you use the right disc: particle diamond for paving blocks and stonecutting for slabs.

Laying A heavy club hammer is ideal for driving wooden pegs and tapping slabs into position (with a piece of timber offcut).

Pointing As an alternative to traditional mortar, try a vacuum-packed sand jointing compound. It reacts with the air and hardens to a permanent, weed-resistant finish.

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Planning

Planning your garden

When you are designing major changes, it's a good idea to draw a simple plan of the house and garden to show where landscaped areas will be. It should also indicate any changes in level, because once out in the garden even slight gradients can present construction problems if they weren’t thought about at the planning stage. Before you make any final decisions, use lengths of string to lay out your proposed plan on the ground.

Preparation

1 Start by marking out the area to be paved with builder’s line and pegs. Check the corners, using a builder's square. Then cut the turf in strips with a spade and roll it up - clearing an area slightly larger than the paved area will be.

2 Dig out the area - allowing enough depth for the hardcore sub-base (100mm in firm, welldrained soil; deeper in soft ground) plus the depth of the paving slab and 50mm mortar. Note: When a patio is built next to a house, the surface of the paving must be at least 150mm below the damp-proof course.

3 Use pegs to mark the finished hardcore level (remembering to allow for an adequate fall – see ‘drainage’). Fill the sub-base with hardcore to just above the top of the pegs then compact it down, using an earth rammer or plate compactor, shown here, which you can hire easily. Finally, cover the surface with a thin binding layer of sharp sand and rake it level.

Once you've prepared the site, dry-lay the paving slabs to check the size of the area and make sure that your chosen pattern will work.

Setting the fall

Paved areas must have a slight slope or fall so that surface water drains away. Generally, it is only necessary to have a fall in one direction: the surface in the other direction can be level. In normal conditions, the ideal fall for a patio is 1 in 80 (that is, a 12.5mm drop in level per metre); for a path about 1 in 80 (across the width); and for a drive about 1 in 40. This is achieved in practice by using a spirit level, a 1m-long straightedge and a shim, a small strip of wood cut to the depth of the required drop in level per metre (see chart).

Setting the fall in the sub-base

First decide which way the paving will slope. If you are building a patio against the house, it must slope away from the walls. Cut a number of softwood pegs. Measuring from the top of each peg, mark them with the depth of the sub-base. Hammer in a row of these pegs across the high side of the site. Cut a shim to the correct size and nail it to the underside of one end of a 1m-long straightedge. Then hammer in the next row of pegs in line with the first, exactly one metre away. Place the straightedge between two pegs with the shim on the lower peg and lay a spirit level on top. A level reading means that the lower peg is deeper by the exact depth of the shim: the correct amount to give the fall you need. Repeat this process at metre intervals across the entire area to be paved.

Setting the fall in the paving

Although the fall is already established in the sub-base, it's important to run builder's lines marking the top edges of the paving to ensure you maintain the correct slope as you lay the slabs.

1 Mark out the edges of the patio with builder's lines attached to pegs. Use a builder’s square to make sure the corners are true right angles.

2 Hammer pegs at the four corners of the patio to mark the finished slab height. Allow a depth of at least 25mm for the mortar. To check the fall, rest a straightedge and spirit level between opposite pegs at the high and low ends of the site. The depth of the shim on the lower peg needs to be the drop per metre multiplied by the length of the paving. Check that the pegs are level in the other direction. Fix lines between the pegs, nailed into the top with large-headed nails.

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Laying the slabs

To achieve a symmetrical design with no unsightly narrow gaps at the skirting, find the centre of the room (for details on how to do this, see you can do it – the complete B&Q step-by-step book of home improvement and work from there towards each wall.

1 Place mortar on the ground should also have a fall of 1 in 80. for the slab. Wet the back of the slab with a brush (this helps it stick and makes it easier to slide into position). Then carefully lay the slab on top of the mortar.

2 Use a rubber mallet or a club hammer and a piece of timber to tap the slab into position. Fill any gaps under the slab with mortar, cutting it flush with the edge as you go.

3 Starting from your key slab, lay the first row of slabs in the direction of the fall. Fit 10mm spacers in all the joints to make sure they are the same size.

4 When the first row is complete, lay slabs along the two adjacent outer edges. Fill in the central area, working back row by row. Keep checking that the fall is correct and that the slabs are level in both directions.

Filling the joints

Leave the mortar to set for 48 hours before walking on the slabs. Only then can the joints be filled. If the slabs are wet or it looks as if rain is imminent, wait for a drier day.

1 Mix a dry mortar of three parts sharp sand to one part cement. Remove the spacers and brush mortar into the joints. When all the joints have been filled, push the mix down firmly with a trowel or a piece of wood, then brush in more mortar. Repeat this process three or four times or holes will appear in the mortared joints. Finally, carefully brush away all the excess mortar – take time over this, as it’s easy to end up with mortar on the slabs.

2 Use a watering can with a rose attachment or a spraying device, lightly wet the whole surface. This will make the mortar set.

3 Dry jointing compound
Alternatively you could fill the joints with dry jointing compound, shown here. Simply brush it in and compact with a jointing tool. It dries hard in a few hours – protect it from rain until then.

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Drainage

Paved areas should have a slight slope or fall, so that surface water can drain away. For a patio, you'd usually want a fall of around 1 in 80 (a 12.5mm drop in level per metre). In some cases, particularly if you have a large paved surface or heavy clay soil, you may want to build a drainage channel, which should also have a fall of 1 in 80.

Cutting slabs
You can cut a concrete slab with a sharp bolster chisel and a club hammer on a bed of sand. Mark the cutting line in pencil (on all four sides of the slab). Then cut a groove, working gradually deeper until the slab breaks. Alternatively, for a quicker, cleaner cut, use an angle grinder with a stone cutting disc. Remember to wear safety goggles, ear defenders, heavy gloves and a dust-mask.

To cut a curve, mark a line with a pencil and a length of string (held taut from the opposite corner of the slab). Cut carefully along the line with an angle grinder, then break off the surplus piece with a rubber mallet and smooth the edge with the angle grinder.

Filling the joints
Mix a dry mortar of three parts sharp sand to one part cement. Remove the spacers and brush mortar into the joints. Push the mix down firmly with a trowel or a piece of wood, then brush in more mortar and repeat this three or four times. Carefully brush away any excess mortar and lightly wet the whole surface, using a watering can with a rose or a spraying device. This will make the mortar set.

Safety first

Look after your back! If you're laying slabs of 600mm x 600mm or larger, you must have help to lift and lay them.

Building a step
You can cut a concrete slab with a sharp bolster chisel and a club hammer on a bed of sand. Mark the cutting line in pencil (on all four sides of the slab). Then cut a groove, working gradually deeper until the slab breaks. Alternatively, for a quicker, cleaner cut, use an angle grinder with a stone cutting disc. Remember to wear safety goggles, ear defenders, heavy gloves and a dust-mask.

Manhole covers
If there is a manhole in the area you are paving, you can disguise it with a recessed manhole cover. If your finished paving is higher than the original ground level, you may have to raise an existing manhole cover.

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Laying loose paving slabs to make a path

Rustic-looking slabs make an attractive stepping-stone path - and you don't need to bed them in mortar.

Start by laying the slabs in place, to get the spacing and arrangement right. Dig out an area of soil, tamp it down well and make sure it’s clear of vegetation. Then add a 25mm bed of sharp sand. Smooth the sand and check that it's level, then lay the slab on top - taking care that the surface doesn't protrude above the level of the surrounding turf. Fill any gaps around the slab with soil or sand.

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