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Laying a patio

Installing a patio is an excellent way to get more out of your garden. A patio can be an area for relaxing and entertaining, but it also acts as a transitional space between house and garden. A patio is low maintenance, hard wearing, and relatively simple to lay. Laying a patio also offers a chance to be creative with design and construction, thanks to the wide variety of paving slabs now available.


    Is laying a patio difficult?

    The steps involved in laying a patio are relatively simple, although they are a little time-consuming. But as with most DIY tasks, thorough preparation and planning will make the project much easier. 

    Once you’ve identified where you’d like your patio to go, it’s a good idea to draw a detailed plan to scale on graph paper. Make sure you include all the relevant measurements and mark down any permanent features such as your house, any fencing, etc. You may want rows of paving slabs that are all the same size, or you may prefer a pattern that uses different sized slabs. If you are using slabs that come from different pallets, it’s a good idea to mix them up to disguise any variation in colour. 

    Having planned your patio you should ‘dry lay’ the slabs out in your preferred design. This is an excellent method of visualising the finished patio and double checking that your measurements are correct. Allow for the right joint size between each slab. Take a photo of the layout for future reference. 

    If your patio will be directly next to your house then its surface needs to sit 150mm below the damp proof course of the house.


      Staying safe

      • Wear suitable footwear and gloves when handling slabs, sand, gravel or cement, and when digging.
      • If using a wacker plate, you should wear ear defenders and steel toe-capped boots.
      • When using a mortar mix, or Slablayer, wear a dust mask, safety goggles and protective gloves and be sure to follow manufacturer’s instructions.
      • Wet and dry cement can cause irritation and burns, so handle carefully, covering skin and immediately washing off any cement that accidentally makes contact.
      • Always wear protective gloves, safety goggles, and a dust mask when mixing concrete.
      • If you're using heavy paving slabs or lifting any other heavy items, ask someone to help.

      Aftercare

      • Patios are hard wearing and easy to maintain but regular brushing and washing will stop the buildup of algae and will keep your patio looking in top condition.
      • The joints are key to your patio’s stability, so look after them by filling in any gaps that appear over time and removing any breakthrough weeds.

      Safety measures to take when laying a patio

      Paving slabs can be very heavy. We recommend working with one other person to reduce the strain of lifting and moving paving slabs. 

      Always wear suitable footwear and gloves when handling slabs, sand, and cement, and when digging. If you use a wacker plate, you should wear ear defenders and steel toe-capped boots. 

      Wear a dust mask, gloves and safety goggles when mixing and handling mortar, cement or Slablayer. 

      Wet and dry cement can cause skin irritation, so always wash with soap and water if any comes into contact with your skin.

      Step 1

      Before you start digging, use a CAT tool to make sure there are no hidden pipes or cables where you intend to dig. Pipes and cables should be at least 450mm below the surface.

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      How much sub-base layer do I need for a patio?

      Once you’ve decided the layout and location of your patio you need to prepare the sub-layer upon which the stones will sit. Start by marking out the area using wooden pegs and builders line (or string).

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      Step 2

      Use a set square to check the corners are exactly square. As a final check measure the diagonals, which should be the same length. If they’re not, adjust the edges as necessary.

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      Step 3

      The next step is calculating the necessary fall of your patio. A necessary fall is a gentle gradient in the sub-base that allows proper drainage and makes sure water runs away from the house.

      The ideal gradient is 1 in 60, which is a 16mm drop in level per metre. To calculate the fall:

      • Multiply the required fall, e.g 16mm, by the length of the sloping side of the patio. This gives you the total difference in height between the highest and lowest points.
      • For example a patio 4m long requires a total fall of 64mm – 4 x 16 = 64mm.

      For textured paving slabs, you can use a slightly shallower gradient of 1 in 80, which is a 12.5mm drop in level per metre.

      Mark the outline of your patio with a lawn edger to keep the lines straight. Then remove the pegs and string. If you mark the edges on the outside of the string, the extra margin will result in a firmer foundation.

      Cut the turf into strips with a lawn edger and remove using a spade. Roll the turf up and save some of it in case you need to fill in any gaps between the lawn and the patio later on.


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      Step 4

      Now you need to calculate how deeply to dig. The depths will vary depending on how you construct your sub layer and how thick the paving slabs are. For this project we’re allowing for a total depth of 175mm:

      • 100mm of MOT type 1 granular hardcore
      • 25mm of Slablayer
      • 50mm thick paving slabs

      Remember to include the necessary fall in your calculations.

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      Step 5

      Pegging out the final surface level of the sub-base is a great way of ensuring you’re maintaining the right depths across the dig. The aim is to make sure your sub-base layers reach the top of the pegs. Take a wooden peg, and from the top mark the finished depth of the hardcore layer.

      Hammer in a row of these pegs 75-100cm apart across the highest side of your site, making sure the marked line is level with the earth. Use a long piece of timber and a spirit level to make sure the pegs are level across the row. Repeat this process for subsequent rows, making sure you maintain the necessary fall.

      Add the hardcore mix so it ultimately reaches the top of the pegs. Here we are adding the hardcore in 2 x 50mm layers for extra stability. But you can add it all in one go if you wish.

      Add 50mm of hardcore and rake over so it’s roughly level. Then compact the layer using a wacker plate or a tamper. Repeat this process for the second 50mm layer.


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      Step 6

      Now add the Slablayer, raking it out to a depth of 25mm.

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      Step 7

      Use a spray gun, or a watering can with a fine rose, to apply water to the Slablayer. Then rake again to level the surface.

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      How to lay paving slabs

      Step 1

      The first paving slab you lay down is the most important one, and is known as the key slab. It provides a guide for the others, so it needs to be positioned correctly and sit level. The best starting position is in the corner at the highest point of the patio. Dampen the underside of the first slab and lay it down.

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      Step 2

      Gently tap down on the surface with a rubber mallet to bed the slab in. If you don’t want to tap directly onto the slab then use a block of wood to protect the stone.

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      Step 3

      Once you have positioned the key slab, laying the rest of your slabs is quite straightforward. You can either work row by row, or follow a sequence you decided on beforehand. Remember to leave joint gaps between the slabs, and use spacers to maintain a consistent gap. You can use wood offcuts to cut your spacers to size.


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      Step 4

      Use a spirit level to regularly check your levels as you go along. The stones should all lie flat so they can bed into the mortar properly, but the fall needs to be accurate. You’re aiming for a flat surface which gradually and evenly slopes downwards as required.

      Slablayer needs at least 48 hours to dry, so cover the patio with plastic sheeting if rain is forecast.

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      How to point a patio

      Step 1

      For joints less than 5mm wide, use a soft bristle brush to sweep kiln-dried sand into the joints. Then sweep any excess off the finished patio.

      For medium sized joints (5-10mm wide), a dry mortar mix is best. Use one part sand to one part cement. The addition of cement results in a firmer mixture that will set naturally as it absorbs moisture from the ground.

      Gently and gradually fill the joints as before, making sure to quickly sweep any cement off the slabs to prevent staining. Compress the mixture in the joints and keep adding until the joints are full.

      A wet mortar mix is most suitable for larger joints (more than 10mm wide). Mix four parts sand and one part cement in a bucket and add enough water so that the mixture becomes smooth and damp. Work the mortar into the joints using a trowel, compressing and smoothing as you go.

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      Step 2

      Carefully brush any excess mixture away from the paving slabs before it has a chance to stain the surface. Wait for at least 24 hours before using your new patio.

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