How to build a patio

Summary: Learn how to lay a patio, prepare the ground, construct a timber frame, fill with hardcore and lay patio slabs.

Laying a patio requires careful planning. If the patio is to abut against the wall of a house, the top must be at least 100mm (4in) below the damp-proof course. Other factors to take into consideration include:

  • The size and design of the patio
  • The position of the patio in the garden
  • Whether to use pavers, slabs or a combination of both
  • The colour of the slabs and/or pavers
  • The pattern in which you are going to lay them
  • Whether to edge the patio
  • Drainage

Once you have made up your mind on all these important matters you can begin to build your patio. For the purpose of this project we are looking at how to lay a small garden patio using slabs.

Once you have marked out the shape of your patio, use a spade to cut the turf around the perimeter.

Preparing the ground

  • Start by marking out the shape of the patio using wooden pegs and string.
  • Knock the pegs into the ground and tie the string between them, keeping it tight. Use a builders’ square to check the angles at the corners.
  • With the shape of the patio marked out with string, use a spade to cut the surface of the turf around the perimeter of the patio. When you have done this remove the string lines.
  • You are now ready to dig the foundations for the patio. When calculating the depth needed for the patio, you must include hardcore, mortar and slab depths. Generally you will need 100mm (4in) of hardcore, 2-3 cm (¾ in – 1 ¼ in) of mortar, plus the depth of the slabs which will vary.
  • Dig down to the required depth remembering that the patio’s surface should not be higher than the surrounding area.
When the frame is in place check the depth of your excavation, removing more soil if necessary.

Constructing the timber frame

  • Now you need to construct a timber frame the same depth as the excavation. The timber must be treated with wood preserver prior to fitting around the sides of the excavated area.
  • The timber frame must be constructed with a slight slope away from the house that has a gradient of 1:50. You can use a laser gradient level to do this. For small areas a gradient or fall of 40mm (1 ½ in) in 2m (6ft 6in) will be sufficient.
  • To achieve this position two pegs in the corners of the excavation 2m (6ft 6in) apart and tie a length of string between them at ground level. Use a spirit level to ensure the string is horizontal.
  • At the end where you want the patio to drain, lower the string by 40mm (1 ½ in). The string now indicates where the top edge of the frame should be. Repeat this operation on the opposite side.
  • Pegs will need to be inserted at the back of the edging at 1m (3ft 3in) intervals to give the frame support. Nail through the edging boards and into the pegs to make the edging secure. Check the corners of the frame are square.
  • When the frame is in place check the depth of the excavation again, removing more soil if necessary.

Hardcore

  • Spread hardcore over the base of the excavation to a depth of approximately 100mm (4in) and rake it level.
  • Using a compacting plate, compress the hardcore. Check the level of the surface, adding more hardcore to low areas, ensuring there is a slight gradient corresponding with the fall of the patio.
Position the first two slabs on the bed of mortar and insert the spacers. Tap the slabs into the mortar with a rubber mallet.
When the mortar has set, use a pointing trowel to fill the joints between the slabs with mortar.

Laying the slabs

  • The most common way to lay patio slabs is in a brickbond pattern. Starting from one corner, dry lay the slabs down the edges, inserting spacers cut from timber offcuts between the slabs. Do not fix them in place until you are satisfied with the design.
  • Cut any slabs to the required size with an angle grinder. Wear protective goggles to do this.
  • The mortar mix should be quite stiff (not too much water): 1 cement to 4 sand. 
  • To lay the slabs in place, spread a bed of mortar 2-3cm (¾ in – 1 ¼ in) thick on top of the hardcore, enough to lay the first two slabs. Position the slabs and insert the spacers. Tap the slabs into the mortar with a rubber mallet.
  • Continue to lay the slabs. Use a spirit level to frequently check that the level and gradient are being maintained. If necessary add or reduce the amount of mortar under the slabs to maintain the correct level.
  • When you have finished, leave the patio for 24 hours. Do not walk on the patio in this time to allow the mortar to set. If bad weather such as rain or frost is forecast, then cover the patio with plastic sheeting and secure it in position with bricks.
  • When the mortar has set, use a pointing trowel to fill the joints between the slabs with mortar. Clean any mortar from the surface of the slabs as you progress.
  • Smooth the mortar between the joints with a brick jointer or leave the mortar flush with slabs. Flush joints drain better.
  • Brush along all the joints with a clean paintbrush to finish the pointing.

Tools needed

  • String line
  • Tape measure
  • Builder’s square
  • Spade
  • Shovel
  • Spirit level
  • Claw hammer
  • Compactor plate
  • Angle grinder
  • Safety goggles
  • Builder’s trowel
  • Rubber mallet
  • Pointing trowel
  • Brick jointer

Materials needed

  • Patio slabs
  • Timber edging boards
  • Wood preserver
  • Nails
  • Hardcore
  • Cement
  • Sand
  • Plastic sheeting

Laying a patio video

Summary: DIY video showing you how to build a patio.

Poor foundation preparation is one of the most common construction faults when building a patio. This can result in the patio breaking up and sinking in sections. Get this right before you start to lay your patio.

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