Laying or Paving Garden Slabs for a Patio

June 5, 2008

Laying or paving garden slabs, clear any debris where the garden slabs will be placed. Patios must have a built in slope away from the house which is imperceptible to the eye. Hammer a peg into the ground near the house at the edge of your patio. Take the 2 m length of batten. Rest one end on the peg, and hammer a second peg in 2 m away from the first. To make a slope, this peg has to be lower than the first, so hammer it further into the ground. Rest the batten on top of the two pegs and measure the difference in height using the spirit level. The bubble in your spirit level should just touch the outer line in its window. Adjust the height of the second peg if you need to. This makes the slope about right - the ideal gradient is about 1 in 60 - a fall of 1 mm for every 60 mm of distance. Water won’t drain away from a smaller slope. Leave pegs in the ground to work to as you excavate.

Paving can be laid directly onto a 50 mm layer of sharp sand on top of well tamped or firmed soil. For greater stability, lay paved patios on a bed of firm foundations throughout the area. Your finished patio level will consist of the thickness of the slabs, plus 75 mm of dry foundation mix to bed them in, and a minimum 75 mm layer of hardcore, depending on conditions in your garden. Allow at least 150 mm below the level of your damp proof course and dig down another 150 mm plus slab thickness for the foundations. Remove the topsoil if it is a new patio, or clear the area. Spread an even layer of hardcore 75 mm deep over the area finishing it to your levelling pegs. Firm with a piece of timber or roller it down.

Cover the area with a semi-dry foundation mix of 6 parts sandy ballast: 1 part cement. Firm this with a piece of timber and check that you have allowed enough depth for your paving slabs to finish 150 mm below the damp proof course. Lay a small test area of slabs to make sure you are happy with the laying pattern and to check on the finished area. Make joints about 10 mm wide for pointing - this will vary according to the type of slabs and your laying pattern. Follow manufacturer’s laying instructions.

Start at the back of the house, if your patio adjoins it. Lay the first corner slab on a bed of mortar - mix 3-4 parts building sand: 1 part cement. Use a wooden or rubber mallet, or the handle of a lump hammer to tap the stone into place. Check that the level is right with a spirit level. Repeat the process, easing slabs into position. Ensure that the joints are evenly spaced - use small timber spacers if necessary.

When you have finished laying the slabs, point the joints, using a semi dry mortar mix of 3 parts building sand: 1 part cement. The mix should be neither too wet nor too dry. Give joints a neat, concave finish, and scrape excess mortar off before it dries. You may prefer to sweep a dry mortar mix into joints, or to fill joints with gravel and the seeds of low growing plants.