On private patio and driveway projects, a fall of approximately 1:60 is usually adequate. Bear in mind that heavily riven paving may require additional fall to prevent water accumulating on the surface, which can lead to discolouration, while smooth ground paving can often cope with a shallower fall (say 1:80).

Falls are formed at sub-base (or sub-grade) level; that is, the sub-base is laid, levelled and compacted to the requisite falls, so that subsequent construction layers (laying course and the paving itself) are all of a fairly uniform thickness.

Sub-Grade

All paved area should be excavated down to the appropriate depth and have some form of sub base or foundation lay installed. The foundation lay is the key to providing the structure strength for the paving to be founded up.

If the area to be paved is such that it requires raising or elevating to a higher level, then the uplift should be constructed by including or adding to the sub-base layer, not by increasing the thickness of the bedding layer.

For driveways or other heavy use, the sub-base layer is the load-bearing layer and should be at least 150mm thick, minimum. For footpaths, this may be reduced to 100mm.

Alternatively, the flags can be laid directly onto a mass concrete sub-base but this is only really required in high load applications – for example a vehicle crossing.

Remove all weeds and other unwanted organic matter. Excavate any soft spots and fill with compacted sub-base material or a 10:1 grit sand/cement mix. Where the area of the paving is troubled with weeds, treat the excavated sub-grade with a general weedkiller.

Bear in mind that topsoil is regarded as an organic material which decomposes over time, causing settlement, and so ALL of it must be removed. It is bad practice to lay any form of paving or surfacing over topsoil.

Because most gardens have at least 150mm of topsoil, it’s often much simpler to remove all of it, to a depth where a firm and stable sub-soil is revealed, and then install a sub-base before laying the paving on a full mortar bed.

Weed or root barriers are not essential unless there is known problem with roots or invasive, deep-rooted weeds, but it is unlikely that any weed will be able to penetrate the upper layers.

Where the excavated ground is suspect or unreliable, use of a construction geo-fabric may be beneficial.

The finished surface level of any sub-base, should be (flag+bed depth) ±10mm below finished paving level.

For light patios and pathways, the bedding material can be a 10:1 mix, which is adequate for most purposes. A stronger mix (6:1) may be used when working in wet areas, or where the movement of ground water could lead to bed migration, and we find it useful beneath the thinner patio flags as it gives the finished pavement a bit more solidity.

Coverage rate for bedding material is approx. 10-12 m² per tonne at 50mm thick, but this varies with moisture content.

Bedding layer

Flagstones can be bedded directly onto either:
a cement bound bed approximately 20-40mm thick
a coarse, grit sand bed, approximately 40mm thick

In general, most flagstones are laid onto a cement-bound material (a mortar or concrete). However, an unbound sand or grit bed can also be used when the situation warrants it.

When working with an unbound bed, DO NOT USE BUILDING SAND – it is too soft and can become ‘fluid’ when waterlogged, consequently moving beneath the flags, causing settlement,

For light patios and pathways, the bedding material can be a 10:1 mix, which is adequate for most purposes. A stronger mix (6:1) may be used when working in wet areas, or where the movement of ground water could lead to bed migration, and we find it useful beneath the thinner patio flags as it gives the finished pavement a bit more solidity.

Coverage rate for bedding material is approx. 10-12 m² per tonne at 50mm thick, but this varies with moisture content.

Individual Bedding

A spade or large trowel to level out the bedding material, which should have the top 15-25mm loosened to allow the flag to be bedded down – this is usually acheived by ‘rippling’ the bedding surface, creating small troughs and peaks with the blade of a trowel. The bed should be 5-8mm high to allow for consolidation. Use the taut string line as a guide – use a piece of broken flag or a piece of timber cut to the correct thickness to judge the level of the bed adjacent to the line.
Make the prepared bed spread 100mm or so further than the flag will cover – it is better to have the bed to big than too small, leaving an edge of the flag unsupported.

Screed Bedding

The bedding material is spread out over the area to be paved, compacted lightly with a plate compactor (around 2 or 3 passes) and then screeded to level 5-8mm high to allow for final compaction.

Flags at a Free Edge

Where flags are laid to a free edge, that is, an edge where there is nothing firm or solid against that edge, as is the case with a garden path and some patios, the edge flags are often best bedded onto a wettish mortar in order that they are held firmly in place. As the mortar (or a suitable concrete) cures and harden, it holds the flag fast and prevents lateral movement.

The very end of the slab can be hauched up with mortar or wet concrete to fully secure it to bedding mortar and to prevent movement