Laying A Patio - A Brief Guide
Concrete paving slabs are an attractive and practical choice for a front garden - but any large area of paving needs a firm base.
Laying out Your Patio Paving Area
Start by marking out the area to be paved with builders line and pegs.
Check the corners, using a builders 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.
Digging Out For Your Patio
Dig out the area - allowing enough depth for the hardcore sub-base (100mm in firm, well-drained 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.
Foundations For Your DIY Patio
Use pegs to mark the finished hardcore level (remembering to allow for an adequate fall. 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.
Laying the slabs
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
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.
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.
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.
Leave the mortar to set for 48 hours before walking on the slabs or filling the joints.
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
A step riser should be at least 100mm, but no more than 180mm.
The slabs forming the front edge of the step are laid on two courses of engineering bricks, which in turn need a 150mm concrete footing to support them.
Dig out the ground for this footing before laying the bulk of the patio slabs, but after you have positioned the key slabs (so that you can use these to set the height of the step).
The slabs forming the front edge of the step overhang the bricks by 40mm.
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.
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.
Tools Ideal for the job
Marking
A 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.
