Building a Patio

Laying a Patio successfully requires planning and preparation, along with a solid foundation. Learn how to lay a simple paving slab patio that will look fantastic and last for years with little or no maintenance. The advice and tips shown here can be applied to a patio two metres square, or 20 metres square.

Marking Out

Plan where you want the patio to be and use wooden pegs and string to mark out the shape. Patio’s usually butt up against a wall of a house, so use this as a guide to laying out the shape of the patio area. If the patio is supposed to have square corners, use a builders square to check that they are all at 90 degrees. Marking out the patio before you start to dig out is important. It lets you see how big your proposed patio will be and see if there will be any obstructions.

Digging out the Foundations

If you want your patio to last for years and remain in good condition (and who wouldn’t?), it is important to properly prepare the foundations. Using the string lines as a guide, mark around the edge of the area with a spade. Cut down through any turf or soil so that there is a clear line all the way around the edge. Once this is done, you can remove the pegs and string.

Dig out the turf and soil to a depth of around 100mm, plus the depth of your chosen slabs and a couple of centimetre’s of mortar. Keep the sides of the foundation hole as straight as possible if you will be lining the hole with treated timber boards (recommended).

Lining the Hole

Cut pre-treated timber boards that are the same depth as the foundation hole and use them to line the edges. The timber should be exactly the same depth or very slightly lower than the surrounding soil. Use a level to make sure that the edging is level and hold the timber in place using wooden stakes.

When all the timber edging is level, use a mallet to lower the edge furthest away from the house (or wall) so that you create a very slight gradient which will allow water to drain off the patio and away from any solid structures. Remember to lower one end of each side so that they slope down to meet the slightly lowered edge.

Laying the Hardcore Base

The next job is to lay and compact the base of hardcore material which will create the solid foundation for the mortar and slabs. Without a good, solid hardcore base, the patio will be much more likely to shift and sag.

Check that the foundation hole is evenly excavated and then start to add the hardcore material. Hardcore can be building rubble, made up of bricks, blocks, stone, sand and other materials. Make sure that there is no wood, metal or plasterboard mixed in with the hardcore as you add it to the hole.

Distribute the hardcore evenly over the area to a depth of around 100mm and level it off with a spade or rake. Ideally, you should use a hired compactor to compact the hardcore properly. Use the edging as a guide and create a slight slope away from the house. If you don’t have access to a compactor, you will have to do your best with the flat of a spade or a home-made compactor made of a flat square of wood attached to a handle. If needed, add more hardcore material to fill any dips or holes in the surface.

Laying the Slabs

laying a patioIt is a good idea to lay the slabs dry, allowing for mortar joints, so you can plan out how many slabs need to be cut, etc. You can lay slabs in any pattern you like, even as a simple grid, but something like a brick-bond pattern will look nicer without being too complicated. Using a stone saw or angle grinder, cut any slabs that need to be cut before you start, and make sure you have all of your tools ready to start laying the slabs on mortar.

Mix up your mortar and lay a bed about 3cm thick for the first slab. Lay the slab in the mortar and make sure it is sitting firmly with no movement. Lay mortar for the second slab, working along one edge, and lay the slab in place. Use offcut pieces of batten as spacers between each slab to ensure evenly sized joints. Continue to lay slabs in this way, mixing up more mortar as you need it (don’t mix up too much at once until you are confident you can lay slabs with little delay). Use a long spirit level laid across the slabs to check they are following the slight slope you need to help shed water.

If any slabs are too low or higher than the surrounding slabs, simply lift them up and add or remove some mortar to even them out. When all the slabs are laid, wait at least 24 hours before walking on any part of the patio. If it looks like it will rain overnight, or if frost is likely, cover the patio with plastic sheeting or tarpaulin. To finish the patio, push mortar into the joints and point them using a trowel or brick pointer.