Laying Paving Slabs
Digging Out
Firstly you should plan out your area and include a fall to ensure water will drain away. We would suggest something like 1:40 cross fall and 1:80 end fall drainage. Also take into account the thickness of the paving, sub base and bedding layer to ascertain how deep you need to dig out. Remember that if you are laying paving up to a building then your finished top level needs to be at least 150mm below the DPC. (damp proof course)
Sub Base
The sub base is the layer that takes the load and gives your paving strength and durability. It isn’t essential to include a sub base in every application but It’s recommended in most cases to prolong the life of your paving application. A sub base would usually be about 150mm of a DTp1 aggregate (This is usually a crushed rock mix) well compacted, leaving little or no gaps for the bedding layer to run into. The sub base should be even in thickness and the finished sub base should reflect the final profile of the finished paving.
For applications such as drives (or other surfaces which will be supporting heavy objects) you should use thick slabs and a sub base of concrete – consult an expert for more details if you’re in doubt.
Bedding Layer
The bedding layer is the material that holds and supports the paving slabs. The Bedding material is a coarse grit sand mixed with dry cement to the right level which will leave the stones flat and level. Do not use building sand – it’s too soft. A 10:1 mix of sand/cement is around appropriate as this will stiffen the mix suitably. The thickness of the bedding layer will be determined by the variation of thickness of your paving slabs. The bedding layer needs to “make up” the thickness of the thinner stones to ensure a level final result. You need to know how thick your thickest stones are to calculate how much bedding layer to allow.
Laying
Before laying the slabs spread out an area of bedding mix and compact it down. Take care to check the thickness of the slab to be laid and level the bedding mix accordingly. Use a trowel to slightly ripple the bedding mix this will allow the stone to “bed down”. Now it’s time to lay the stones. Smaller ones can be lifted into place but larger stones should be carefully tipped from an already paved or solid place. Use a “maul” (a big, rubber-headed hammer) to help you align the stone. Take care as certain rubber hammers can leave marks on the stone. Some form of protection such as laying out a cloth over the stone may be required. Then tap lightly towards the edge of the stone to make it flush with the others. When you’re satisfied, stand on the flag and check that it doesn’t rock around, that the bed is good and the stone is flush with the surrounding stones. If the stone is too high or low, you’ll need to lift it, add or remove some bedding, and replace it.
Jointing or Pointing
Dry Jointing – Our recommendation here is to brush in a dry mix of sand and cement as long as the paving is completely dry and there is no chance of rain. A 4:1 mortar mixture is mixed dry then spread over the finished paving. Using a soft brush you sweep the mix into the joints. Each joint is then packed down with the edge of a trowel or similar implement to pack the dry mix into the joints. this process may need repeating several times to ensure a good solid joint. Obviously any residue on the surface needs to be swept clean to avoid any cement staining the stones.
Pointing – possibly more time consuming but can achieve longer lasting results. Mortar is mixed wet and toweled into the joints. Using two trowels can speed the process, holding mortar on a large trowel at the edge of the joint and feeding it into the joint with a smaller trowel. This will also help minimise any staining on the edges of the paving slabs. The mortar will need to be pressed down into the joint and then finished with a jointing trowel.