Step-by-step advice on laying paving slabs
Building a patio, or paved area, can be a great way to add a practical, low-maintenance space for relaxation and entertaining in your garden.
Whilst constructing a sub-base and laying paving slabs can take some time, the techniques used are relatively simple and it’s possible to complete a small project in a weekend. We recommend asking a friend or family member to help, making the heavier work easier and speeding up the process.
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In this project, we’re going to:
- work on flat, level ground that is not adjacent to a building – so we won’t need to take into account a damp-proof course
- create a sturdy sub-base to lay our patio on
- lay a square-shaped patio using square paving slabs
- lay the paving slabs in a stretcher bond pattern
We’ll show you how to:
- measure, mark out and dig out the sub-base area
- lay the sub-base
- lay the paving slabs
- cut paving slabs to fit
- joint the patio for the perfect finish
Still deciding on your preferred paving? Head to our Paving buying guide for advice and inspiration to help you choose the right paving slabs for your patio.
Our video guide below is the perfect place to start with your project.
- Paving slabs can be very heavy. If you are laying slabs 600 x 600mm or larger, you must have someone to help you lift and lay them. We recommend always working with a friend or family member to reduce the strain of lifting.
- Before you start excavating the sub-base area, use a hired cable avoidance tool (CAT) to check for any underground pipes or cables for gas, water, electricity, telephone or drainage services. Pipes and cables should be buried a minimum of 450mm below the surface, but you can’t always be certain that this is the case – especially with older properties. If you find buried pipes or cables, you can employ a professional to relocate these, or consider an alternative location for your patio.
- Cement, either wet or dry, can cause skin irritation, so always ensure you wash with soap and water if it comes into contact with your skin.
- When operating a plate compactor wear steel toe-capped boots, safety goggles and ear protection.
- Wear safety goggles, gloves and a dust mask when mixing mortar to avoid cement coming into contact with your skin or eyes, or being inhaled.
The first step in creating your new patio is marking out the space.
You’ll also need to calculate and mark out the fall. The fall is a slight slope across a paved area that helps surface water to drain away easily. A patio is still level with a fall as the gradient is so gradual.
If possible, dry lay the patio to check that your measurements are correct. This is also an opportunity to mix up paving from different pallets – important if you have natural stone slabs as it’ll help to blend any varying shades.
Lay out the paving slabs in the desired pattern, either where you plan to build your patio or on a clear, flat area of lawn. Allow for your preferred joint size between each slab.
Measure the length and width of the paving area to confirm the final dimensions of your patio. Move the slabs out of the way, making a plan on paper of what goes where so you can put them back in the same location.
Mark out the area for the sub-base using wooden pegs and a builders line. Ideally add an extra 5 to 10centimetres (cm) to every edge of the patio measurement. This will make the sub-base slightly bigger than the finished patio giving it a more secure foundation.
Place a wooden peg in each corner and run a builders line between each peg to provide a straight edge for the sides of the patio. Use a builders square to make sure the corners are square.
As a final check, measure the diagonals to make sure they are the same length. If they’re not, measure each side again and adjust until your diagonals match.
Calculate the fall for your patio, using the final dimensions confirmed at the end of step 1.
The ideal fall is dependent on the type of paving slabs being laid.
If using textured paving slabs – the ideal fall for a patio is 1 in 80. That is a 12.5mm drop in level per metre.
- If using flat or smooth paving slabs – aim for a fall that is 1 in 60. That is a 16mm drop in level per metre. These paving slabs require a slightly steeper slope as they’re more likely to get slippery if surface water doesn’t drain off quickly.
To calculate the fall:
Multiply the required fall (e.g. 12.5 or 16mm) by the length of the sloping side of the paved area in metres (m). This will give you the total difference in height required between the highest and lowest point of the patio.
For example, if you are building a patio 3m long with textured paving, you will require a fall of 12.5mm per m. Allow a total fall of 37.5mm from the highest point of the paved area to the lowest.
If building a patio next to a house, garage or outbuilding, the paved area should slope away from the walls. You can choose the slope direction if there are no walls on any side.
Cut the turf into strips with a lawn edger (to give a neat line) and lift using a spade.
Roll up and save some of the turf in case you need to fix any gaps between your existing lawn and the paved surface.
Calculate the necessary depth for the sub-base.
For this project, we’re digging to a depth of 215mm at the highest point. This is so we can lay:
- 100mm of sub-base (compacted MOT Type 1 granular hardcore)
- a thin blinding coat of sharp sand or all-in-ballast
- a 50mm layer of mortar
- the paving slab. In this example, our paving slabs are 65mm deep, but measure the depth of your slabs and insert this into your calculation.
All of these layers add up to give the necessary depth for digging.
Once calculated, dig the area to the correct depth using a spade.
Peg out the final surface level of the sub-base.
Take a number of wooden pegs (600mm tall and pointed at one end is ideal – these can either be made or purchased). From the top of the peg, measure the depth of the sub-base (100mm) and mark a line clearly on the peg using a pen or pencil.
Hammer a row of these marked pegs – spread at 1m intervals – across the highest side of the site. Hammer them in until the marked line is level with the excavated earth.
Use a long piece of timber as a straight edge to make sure that all of the pegs are level with each other and remedy if not.
Hammer in the next row of wooden pegs in line with the first, exactly one metre away.
Repeat until all rows of pegs are laid.
Set the fall for the sub-base. This ensures that when the sub-base is laid, the gradual slope of the fall will be present in the sub-base.
Measure and cut a small strip of wood to the required drop in height of the patio per metre. In our example in step 3, we calculated a fall of 12.5mm would be needed. This piece of wood is known as a levelling shim.
Nail the shim to the underside of one end of a 1m-long straightedge.
Lay the straightedge to rest between two pegs – the first peg from the first row and the first peg from the second row. The shim should face down into the top of the second row peg. Lay a long spirit level on top of the straight edge. The reading should show that the second peg is higher than the first one.
Remove the spirit level and straightedge and carefully hammer the second peg until you get a level reading when the straightedge, shim and spirit level are laid on top again. A level reading confirms that the peg has been hammered into the ground at the correct depth for the fall.
Dig, fill or tamp the ground as necessary until the peg is at the right depth.
Repeat Step 8 for all of the pegs in the second row.
Continue with the remaining rows.
With the site dug to the correct depth and pegs in place, it’s time to start laying the patio’s sub-base.
Using a wheelbarrow, tip in enough hardcore to fill your sub-base to just above the top of the wooden pegs.
Compact the hardcore with a plate compactor.
Check that the surface is level with the top of the marker pegs, and add more hardcore and compact again if necessary to reach this level.
Cover the surface with a thin (10mm) layer of sharp sand or all-in ballast and rake it level. This is known as a blinding coat.
Remove the four corner pegs and lines. The sub-base height pegs will remain buried in the sub-base.
Although the fall has already been set in the sub-base, it’s important to run a set of builders lines marking the perimeter of the patio and the top edges of the paving slabs. This will help you maintain the correct slope when you lay the slabs.
Using a tape measure and builders square, mark out the perimeter of the patio with builders lines and timber pegs. Position the wooden pegs so they’re just outside the project area, but aligned with the borders of the final paved area.
Where possible, position the pegs about 30cm outside of the sub-base area, so the string lines intersect to mark each corner (see the diagram below).
Use the builders square to check the corners are square and adjust the lines and position of the pegs if needed.
Take four wooden pegs and mark with a line 115mm from the top. This allows 65mm for the thickness of the paving slab plus 50mm of bedding mortar underneath.
Hammer the pegs into the four corners of the paved area until you reach the mark you’ve made on the peg. The top of the peg will now mark the finished height of the patio.
Using the shim, straightedge and spirit level used to set the fall in the sub-base, check that the pegs are level in the direction of the fall. Remove the shim and check the pegs are level in the other direction.
With the pegs at the correct depth, remove the shim and straightedge and adjust the height of lines above the ground so they run from the top of the peg to it’s opposite. The intersecting string lines should contact one another.
Laying the first slab correctly is key, as it acts as the guide for all the others.
Paving slabs are bedded in a mortar mix with four parts sharp sand to one part cement. Measure your quantities using a shovel or a bucket – for example, four buckets of sand for every one bucket of cement. Mortar will need to be used within two hours of being made (in hot weather you’ll have less time), so mix as much as you think you can use in that time.
A cement mixer will make short work of mixing, but you can also mix smaller quantities by hand on a mixing tray.
Mixing mortar by hand
On a mixing tray, thoroughly mix the dry sand and cement together. Using a shovel, make a hole in the centre of the pile and pour clean water into it. Carefully push the dry mix into the water, letting it be absorbed. Mix it thoroughly, adding more water as necessary. It’s better to add less water to begin with and slowly add more if needed.
The consistency of the mortar is important – it mustn’t be too dry or too runny. To test it, make a depression in the mix with a shovel. If this is easy to do and the mortar holds its shape, the consistency is correct.
Mixing mortar in a cement mixer
Pour about a quarter of a bucket of water into the mixer. Add half the sand, then the cement. Run the mixer, then add the rest of the sand and more water if necessary. Mix it thoroughly until you have a soft consistency.
Top tip: Keep your tools clean
Don’t allow mortar to dry on your tools. Clean them with a stiff brush from time to time. If using a mixer, wash the drum thoroughly after use.
Starting in one corner of the sub-base area (at the highest point), lay about 60mm of mortar on top of the sub-base. You’ll only need to lay enough mortar for the first slab.
Wet the back of the slab with a brush, ready to be laid – this will improve adhesion and make it easier to slide into position.
Carefully lift the first slab and lay it on top of the mortar. This is known as the key slab.
Use a piece of timber and a club hammer or rubber mallet to tap the slab into position. Take great care not to crack the slab.
Fill any gaps under the slab with mortar, cutting it flush with the edge as you go with a trowel.
Once you have positioned the first slab, laying the rest of the slabs is quite straightforward.
Starting from your key slab, lay the first row of slabs in the direction of the slope.
Position spacers in each joint to ensure that these remain the same size. Make spacers by cutting pieces of timber or dowel into short lengths.
Use a long spirit level to check and recheck that the surface is flat and the fall is correct. If you put a slab down and it rocks on the mortar, take it up and re-lay it until you’re happy that it’s sitting correctly.
When the first row is complete, lay slabs along the two adjacent outer edges. If you’re using a stretcher bond pattern, the first and last slabs on alternate rows will be half slabs.
Top tip: How to cut paving slabs
For some paving projects you’ll need to cut paving slabs. An angle grinder fitted with a stone-cutting disc will make light work of the cuts. Mark the cutting line in pencil on both the surface and edges of the slab and use the angle grinder to follow this until you have a clean cut.
Fill in the central area, working row by row. Nail a line to pegs at either end of each row before you begin laying it to help maintain a level surface. Keep checking that the fall is correct and that the surface is flat in both directions.
Once complete, leave the mortar to dry for at least 48 hours. If bad weather is forecast after your paving slabs have been laid, cover the patio with a tarpaulin to protect against rain and wait until a dry day to finish your project.
Remove the spacing pegs once the mortar is dry.
Jointing is the final step in completing your patio. It’s the process of filling the gaps between the paving slabs to provide a firm, level surface.
Depending on the size of the joints between the slabs, different techniques are used to ensure a hard-wearing finish. We’ll show you how to joint three different jointing widths:
- less than 5mm wide
- 5 to 10mm wide
- over 10mm wide
Begin jointing once the mortar is set underneath your paving slabs.
Top tip: Colour your jointing mixture to complement your paving
Cement can be coloured with a special cement colouring agent to complement the finish of your paving slabs. The colouring is added to a dry jointing mix, following the instructions on the packaging. Take care to use the same dosage if mixing more than one batch, to keep a consistent colour.
For joints less than 5mm wide
Using a soft brush, sweep kiln-dried sand into the joints between the slabs.
Finish off by sweeping the surface of the whole patio to ensure that it’s free of loose sand.
For joints 5 to 10mm wide
Medium-size joints are best finished using a dry mixture of sand and cement. The addition of cement leads to a firmer finish and the mixture will set as moisture in the ground is absorbed over the first few days.
Mix one-part kiln-dried sand with one part cement in a clean bucket.
Gently sprinkle the mortar mixture along the joints. Brush in using a soft brush.
As you work, brush away any excess mixture from the surface of the slabs to prevent staining from the cement.
Compress the joints using a jointing tool and keep adding the mix until full.
For joints over 10mm wide
For larger joints, use a wet mortar mixture.
Mix four parts building sand and one part cement in a bucket, adding clean water until you achieve a slightly moist, smooth, damp consistency. Add the water slowly to the mix to help avoid creating a wet or sloppy mortar that runs easily off a trowel or jointing tool.
Work the mortar into the joints using a trowel. Push the mix down firmly into the joints with a jointing tool, and repeat this process until the joints are full, compacting and smoothing as you go.
Carefully brush away all of the excess mortar from the slabs, as the cement could stain them. Use a damp sponge to do this as you work on one joint at a time.