Laying A Patio

Laying a patio is a fairly large project so it’s important to plan well. Get to know the characteristics of your garden before choosing the area you want to pave. Your decision can be influenced by considering which parts of the garden are sheltered from the elements, which parts are not overlooked, where the sun falls during the day etc. When designing your patio it is important to remember that these days there are many designs and techniques to choose from and you don’t have to restrict yourself to boring grey slabs. Laying it yourself can save a lot of money and with good planning can look very professional in the end.

When you know exactly what you want, make an accurate plan as it will help you estimate the amount of material you will need. Don’t forget to plan for features you may want to add later and remember to check for buried services such as pipes and cables. You don’t want them under your paved area.

If you are planning a large area of paving, you can break it up with straight runs of bricks, or leave out random slabs and fill the space with shingle instead.

The first stage of laying a patio is marking out the site with pegs and string. The top of the pegs should be at the height of the proposed finished level. When you have put in the corner pegs, build up from them a grid of pegs matching the size of the patio. To avoid the danger of damp walls you must make sure that the level of the patio at the house wall must be at least 150mm below the damp proof course. In older houses you can sometimes see the slate used for this. Otherwise look for what looks like an extra wide line of mortar in the brickwork. You also have to make sure that the patio will have a gentle slope away from the house (1:40 for most circumstances) in order to prevent rainwater from pooling on it. Large patios should also have a cross fall of 1:80 to improve water run-off. To get the level, use a straight timber batten and spirit level resting on the pegs. Work out what the fall between the pegs concerned should be, then place an appropriately sized off cut of wood on top of the peg. This off cut will have accounted for the necessary fall when the batten between the pegs is level.

The next stage is to dig away the soil, enough for slab thickness plus the layers of the base. You will be able to establish the amounts by measuring down from the top of the pegs. Dig out the topsoil and save for elsewhere in the garden. In order to establish how far you need to dig down below the topsoil, you need to consider in what way you wish to use your patio. For light use, slabs can be laid on a compacted 50mm bed of sand. It is better, however, to go for a 50mm semi-dry mix of sand and cement as this is more stable. A compacted 75mm layer of hardcore (broken brick and rubble which is laid over the ground and compacted, providing a firm stable base) should be added below the sand-cement mix in any area you plan for heavy use. If you are going to use it for vehicles the hardcore bed should be 150mm. You can calculate the volume of hardcore you will need by multiplying the area of the patio by the thickness of hardcore needed. Always allow a bit extra as it will be compacted. In order to ensure that your base will be solid you might want to consider hiring a plate vibrator for the preparation stage.

When the base is ready it is time to lay the flagstones. Once again there is a slight difference depending on the use of the patio. For light use it is enough to trowel five generous dabs of mortar onto the base, then lay a slab in place. Tap the surface of the slab with the end of a club hammer and check with a spirit level in both directions. Don’t forget to allow for the fall. You can use the string between the pegs as a guide. Heavier use will require a 50mm thick continuous bed of mortar, upon which the slabs will be laid. This way they will be fully supported and less likely to crack. If you want to lay paving directly onto sand it is important to level it carefully so that it will support the slabs fully. This is done by putting battens at intervals in the sand with their tops at the appropriate level and drawing a straight edge along them. Battens should be removed and the grooves back filled before paving. Battens left in place will rot.

When laying the slabs there is usually a 5-10mm joint. In order to keep the gap even, you can cut pieces of hardboard and use them as small spacers, wedging them between the slabs. It is best to work your way along the house wall first, then down one side using the guide string, before finally filling in the middle, working diagonally. Remember to check the level regularly.

Slabs which need to be cut can be left until the bulk area has been laid. To cut a slab, score it with a grinder or bolster chisel, then raise the smaller section on a thin batten and tap the main part of the slab along the cut line with the handle of a bolster hammer. You can hire angle grinders, and if you choose to do so be sure to read the operating instructions and, if you don’t know how to use the equipment, also to ask for a demonstration. Wear safety goggles and work gloves when cutting and if you are using noisy equipment, wear also ear defenders.

To finish off your patio, force a fairly dry mortar mix into the gaps with a trowel and brush off the excess before it dries.

photo credit creative commons license rsgreen89