Individual bedding

Screed Bedding

This method requires a screed bed to be prepared before placing the quartzite flags. A relatively large area can be screeded in advance and the flags placed one after the other directly onto the bed.

Whilst obviously more efficient than the individual bedding method, this method is only suitable for the smaller and lighter quartzite flags, which makes it easier to be manhandled onto a screeded bed. It is essential that the flags be of a constant thickness, hence only the calibrated quartzite pavers are suitable candidates.

Construction

There are only 2 layers to flagged light-use paths and patios, while driveways, forecourts and public footpaths should use a concrete sub-base and lay the flagstones directly onto the concrete before it sets.

Preparation

Sub-grade

The surface needs to be dug to a depth of approx 90mm, if no sub-base is required, add 100mm for concrete sub-base, The depth of dig can be calculated as...

(average depth of flagstones + 35-50mm bed + any sub-base required)

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.

Sub-base

This will not normally be required for a path or patio unless there is concern regarding the suitability of the sub-grade. However, any low spots can be filled with crushed hardcore, crushed stone or compacted bedding material - see below.

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

For driveway or other heavy use use, the sub-base layer is the load bearing layer, and should be at least 100mm thick, minimum. For public footpaths, this may sometimes be reduced to 75mm, or increased to 150mm or more to give added protection to underground services.
Alternatively, the quartzite flags can be laid directly onto a mass concrete sub-base, but be prepared to work fast to cover the ground before the concrete sets!

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

Bedding layer

The flagstones can be bedded directly onto a coarse, grit sand bed, approx 40mm thick.
DO NOT USE BUILDING SAND - it is to soft and can become 'fluid' when waterlogged, consequently moving beneath the flags, causing settlement.

The bedding material can be stiffened by the addition of a small quantity of cement, around a 10:1 mix is adequate. This is useful 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 grit sand is approx. 10-12 m² per tonne at 50mm thick, but this varies with moisture content.

The flags should be laid to a taut string line, to aid coursing and levelling accuracy. Basically, a length of string is stretched from one known point of the paving to a projected point, and used to guide longitudinal line/level. A straight-edged timber or long spirit level 1000mm or more) is used to check transverse accuracy. The distance between consecutive line pins should not exceed 10 metres.

Individual bedding

Use a shovel or a 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.

The true art of flag laying is to get the bed right on the first attempt, so that the flag can be laid and consolidated without having to be repeatedly lifted while bed adjustments are made. If you have 100 flags to lay, and it's taking 3 attempts to get each bed right, you've laid 300 flags in actuality, but have only 100 to show for your efforts.

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.

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 can be bedded using a 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.

Buttering or not?

If using a mortar joint, the 'receiving edges' of the previous flags should be 'buttered' with a generous amount of mortar, taking care not to get any mortar on the surface of the flag. The next flag to be laid is then presented to the receiving edges, squeezing against the mortar that has been buttered thereon.

With the dry mortar joint method, where the flags are laid without mortar and a dry sand/cement mixture is brushed into the joints on completion of the actual laying, it is advisable to use small pieces of plywood between the flags to maintain regular 8-10mm wide joints.

Laying the flags

The smaller paving units, such as those shown opposite, are often light enough to be lifted directly into place, but the larger units, 450x450mm and above, need to be lowered carefully into position.

Most flags larger than 450x450mm are relatively heavy and often weigh more than the maximum recommended in manual handling guidance (usually taken to be 25kg). Whenever possible, specialist paving tools and lifting aids should be used when working with these larger units. Returning to unaided manual laying, there are two ways of laying the bigger, heavier flags - from the paved surface and from the leading edge. Note that when using the screed bedded method, work must be done from the paved surface to avoid disturbing the prepared screed bad.

Laying from the paved surface

Walk the flag into a position where the bottom edge is hanging over the lip edge of the preceding unit, roughly halfway, as shown in the diagram opposite. This ensures that when the flag is lowered into position on its bed, it remains relatively 'tight' to the preceding flag.

Make sure you have the flag in the correct orientation, so that it will not be upside down when laid. Holding the top edge of the flag with both hands, squat down behind the flag and lower it carefully into position, allowing it to pull you up out of the squatting position. This technique places less strain on the back muscles than lowering the flag from an upright or stooped stance. Always lay flags the 'narrow' way - ie, if laying a 600x300mm flag, maked sure the 600mm long edge is on the ground and that you are only stretching 300mm to lay the flag.

One technique we use to avoid excessive strain on the back, is to use a rubber mallet to take the bending motion out of lowering the flag. The head of the mallet is used to hold the 'top' edge of the flag, which is then lowered by the tradesman who controls the flag's descent via the mallet.

Laying from leading edge

Walk the flag to be laid into position so that the bottom edge of the flag is aligned to deliver the flag into the correct position. Keeping one foot against this bottom edge to prevent the flag from slipping backwards, grip the flag on the open side and carefully lower it into position on the bed. Make sure you do not get your fingers trapped between the flag you are laying and the preceding unit.

Consolidation

Once on the flat, the flag is nudged into alignment with the mallet , and is then tapped down to the correct level with the mallet until it is 'flush' with the surface of the preceding flags and/or the string line guide. Use light taps on the areas indicated on the diagram. If you tap too near a corner, the flag might break, if you tap too hard over a hollow in the bed, the flag might break, so remember, light taps and plenty of them. Concentrate your 'taps' on the four main areas.

It's too high!

The flag can only be tapped down a limited amount. Beyond a certain point, no futher compaction is possible and if you persist in hammering it with the maul, the flag will break. There is only one remedy, the flag will have to be lifted and re-bedded, but before you do lift the flag, make a mental note of where the flag is high and by approximately how much, then, when you've lifted the flag and stacked it safely while you adjust the bed, you can use a spade or a trowel to reduce the bed in the necessary areas. Once again, looosen the top 15-20mm of the bed and try the flag again. Hopefully, it's right this time.

It's too low!

If the flag is too low once you've consolidated it with the mallet, it will have to be lifted and the bed added to before relaying. Simply lifting one edge of the flag and packing bedding material in as far as your fingers will reach is not a good idea - it can leave a void in the centre of the flag, meaning the flag is only supported on the packed edge and the opposite edge.
Again, make a mental note of where it is low and by how much, lift and stack the flag safely out of the way, and then add bedding material to the entire bed, re-levelling with a trowel or spade before re-laying the flag.

Jointing/Sealing

This is not strictly necessary, as the flags can be laid 'butt-jointed', meaning the edges are close, but not directly in contact with the adjacent flags. These joints should be 2-5mm in width (average 3mm) and should be filled with kiln dried silica sand, as used in block paving applications. Dry jointing works well with square-edged flags, i.e. those that have perfectly straight sides.

For those flags with rough edges, especially the riven copies with 'authentic' or 'fettled' edges, mortar pointing is preferred. As a general rule, if two adjacent edges are more than 5mm apart, a mortar should be used to point them.