In this article we want to outline all the steps involved in laying paving slabs or flags on a screeded bed.
There are two ways to lay paving, on a screeded bed of sand or individually laying of flags on a wet or semi wet concrete mix. Each method has it’s benefits but a screeded bed method can only be used if the paving slabs you are working with are all calibrated to the same thickness. This generally means that the screeded bed method is not suitable for rough cut natural stone.
Where a screeded bed method can be used
- Block Paving
- Man Made Paving Slabs
- Calibrated Natural Stone
Base Layer for Paving Slabs
Luckily, regardless of which bedding layer method you use, the base layer is the same for both. The only variation in the sub base layer is the depth of the layer & this will depend on the traffic type or use of the paved area.
- For Cars: Sub base should be 150mm in depth
- For Walking Only: Sub base layer should be 75mm in depth
Preparing the base layer is the first step in paving. Mark out the patio or path area using string line or spray can then begin excavating the area to the desired depth. To work out the depth of your excavation, you should add the flowing:
Depth of Base layer + Depth of Screed (bedding layer) + Depth of Paving = Depth of Excavation
Generally this would be:
75mm+ 50mm + 40mm = 165mm Depth of Excavation
Once the area is dug to the desired depth, make sure the subsoil is flat and compact. If the ground is very soft you may need to excavate further until you reach compacted earth. If the area is prone to flooding or holds water then you should install a 4″ drainage pipe.
Now you can lay the sub base. Use 804, hardcore, crusher run/ crusher stone or crushed stone. Lay the stone & level it out over the area then compact it into place using a wacker plate, measure the depth of the base & add more stone as required. 1 tonne of 804 covers approx 10 m² @ 75mm compacted thickness.
Screed or bedding layer for paving slabs
This sand layer is the layer that your paving slabs are laid directly on. This is a dry mix so it allows for a bit of trial & error so if mistakes are made you can simply re-screed and start again. The key to a good screed and therefore a quality patio is all about good preparation.
You will need:
- Screeding poles – These are (ideally) metal poles, that are set to the finished height of the bedding layer. It is along these screeding poles that the ‘screed’ is pulled to get a flat & level bedding layer surface.
- Screed – This is a long flat timber post. As mentioned above this is used to pull & drag the sand across the bedding layer to create a flat & level surface
Carefully position flags into place following the desired pattern. After laying, gently tap the flags into the bedding to ensure they are level & not rocking.