What Should Paving Be Laid On?

If you’re thinking about introducing some paving to your outdoor space, it’s vital to make sure you get the installation right first time, in order to save you plenty of time, money and effort.

Part of what’s involved in getting your paving right first time round involves laying it on the right materials. By taking the time to read up on the best materials to position your flagstones on, you’ll be left with a completed paving project that’s bound to last you many years to come.

Here, we’ve detailed exactly what paving should be laid on, so all that’s left for you to do is to gather the relevant materials and get started on adding some quality paving to your garden.

Begin with a subgrade layer

The subgrade layer, sometimes referred to as the formation level, consists of the native material – typically soil – that is already situated within the ground of where your paving will be positioned. The subgrade is the very bottom layer on which your paving will be laid on.

In order to create a subgrade layer, all that you need to do is clear away any grass and topsoil from the paving area, until you are left with a layer of more stable soil. This soil will act as the subgrade layer and should be compacted to withstand the weight of the paving and any furniture or individuals that will rest on the paving.

With a solid subgrade layer in place, you’ll have a strong bottom layer for your paving, as well as a good drainage system for any bad weather that comes your way.

Top tip: When developing a subgrade layer, make sure to dig deep enough to allow for at least 100mm of sub-base layer and a 50mm bedding layer, as well as the depth of the paving stones.

Add a sub-base layer

After your initial subgrade layer comes the sub-base layer, which is typically the “load bearing” layer of your paving area.

The best sub-base materials are those that have excellent drainage properties and can spread the load bearing capabilities across the entire space. Two types of subgrade are unbound granular materials, and cement bound materials. Unbound granular materials are loose yet able to lock together naturally, to create a strong base for load bearing. Bound materials, on the other hand, are materials that have been set or bound together using an agent such as cement. This type of subgrade is more difficult to remove, so if you might want to change your paving area in the future, an unbound subgrade might be the way to go.

Not all paving projects require a sub-base layer, only those that will have heavy objects resting or travelling across the paving regularly. Paving that’s designed to act as a driveway or a hot tub area, for example, are more in need of a sub-base layer than say a pathway or dining area. Of course, you’re free to add a sub-base to any paving project, if you’re looking for ultimate durability from the completed space.

How to prepare a sub-base layer for your paving

If you have already created a subgrade layer, you will have already marked out where you want your paving to lie and will have dug out any grass or topsoil from that area. If not, this is the first thing you will need to do.

From there, you will need to assess and calculate the “fall” for your paving area, to allow for proper drainage. If you’re planning on using flagstones with a textured design, aim for 12.5mm drop in depth for every metre of your paving space. However, if you’ve invested in smooth flagstones for your paving, try to create a fall that’s 16mm deeper for every metre of the space. This is because smoother paving stones are less able to drain away any water naturally and can become slippery without the correct fall.

Top tip: If your paving space is next to a building, make sure the fall slopes away from it and away from any of the walls.

Dig deep enough to allow for each of the layers, as mentioned earlier, so that you have a smooth finish that’s level with the surrounding ground, once your paving stones are in place.

How to lay your paving’s sub-base layer

Once the ground has been correctly prepared, you can go ahead and lay the sub-base material.

If it helps, push a few wooden pegs into the ground, to the height that you want the sub-base layer to reach. From there, you can use a wheelbarrow to tip the materials into the space so that it just about covers the wooden pegs.

Once the material has been spread out across the area, use a compactor to make sure the layer is level and compacted enough to perform exactly how a sub-base layer should.

To finish the layer, evenly scatter a very thin layer of sharp sand across the sub-base, before moving on to the next layer.

Top off with the bedding layer

The bedding layer is the final layer that needs to be added before your paving can be laid. This layer adds some additional support for your paving, holding them in place, and it also allows you to place them at the right height, level to the ground.

A mortar mix or sand are popular materials used for bedding layers and the one you choose to use depends on the paving you had in mind. A mortar mix is the most popular choice and can be used with the majority of paving stones, however, lighter coloured paving is best used with sand, as it’s less likely to suffer from discolouration over time.

Top tip: Never use building sand as a bedding layer, as it is too soft and badly affected by wet weather.

You’re now ready to lay your paving

Once you’ve tackled the subgrade, sub-base and bedding layers, you can move on to laying your paving stones in place. It might sound overly complicated but when you get to it, creating these layers is relatively simple. What’s important to remember is how much longer your paving will last, when you take the time to set its foundations before laying the finishing layer.

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