how to lay global stone paving

Laying flags and slabs onto individual dots, dabs or spots of mortar is sometimes shown as a suitable method, but it really ought to be avoided: it’s not an approved laying technique, and there are good reasons for that.

Firstly, it doesn’t provide full and uniform support for the flagstones. Some parts are supported; others are left ‘bridging’ two spots, which makes them more prone to breaking.

Next, those empty spaces between mortar spots are a recipe for disaster. They allow water to pool underneath the paving, which encourages the growth of algae on the surface, but also destabilises the sub-layers, causing some of the finer material to be washed away. This, in turn, undermines those mortar spots, and the flag starts to rock, pivoting on the spots that haven’t settled or shifted.

Spaces underneath the flagstones also provide an ideal hidey-hole for invertebrates and small mammals that will mine or tunnel through the sub-layers, again destabilising the paving and resulting in settlement or broken flagstones.

Finally, with some types of flagstone, the bedding will alter the porosity of the flagstone and visibly affect the surface appearance. Can you see where the mortar spots are beneath this flagstone?

Global Stone paving is a quality product, and as such, it deserves a quality bed. You wouldn’t lay an Axminster carpet on bits and pieces of old underlay, so don’t lay your Global Stone flagstones on dots and dabs of mortar. Do it right: lay on a full bed of mortar.

While Global Stone’s range of gorgeous clay pavers can be laid in exactly the same way as the more familiar (but not as attractive) concrete block pavers, they can also be laid ‘rigidly’, bedding each of the pavers onto mortar to give a firm, stable and reliable surface that can be used for courtyards, paths or patios. Obviously, rigid laying is more time consuming than the lay-on-sand option, but the results can be visually stunning.

The key to success and the real strength of a rigid clay paved surface comes from the base layer. For most residential projects, this will be concrete.

The base will need to be 100mm deep, formed from a good quality concrete (10 Newtons or 1:3:6 mix) laid over a firm sub-base of crushed stone or hardcore. The clay pavers will be laid onto a mortar on top of the concrete slab, giving a pavement with four identifiable layers, each of which is described below.

Sub-base:
This is a layer of crushed stone or hardcore spread over the excavated ground to act as an ‘improvement’ layer. Where the existing ground is firm and stable, it may be possible to omit the sub-base and to lay the base directly onto the ground, but if in doubt, use the sub-base – better to be safe than sorry!

The best material to use for a sub-base is known as Type 1 (DTp1, MoT1) and is readily available through Global Stone. It needs to be put down as a layer at least 100mm deep and thoroughly compacted using a vibrating plate compactor or roller (which can be hired).

This method of laying clay pavers requires the three uppermost layers (the base, the bed and the pavers) to be reasonably consistent in depth, and so it is important that the sub-base layer is laid to a profile that will match that of the completed pavement. So, if the pavers will drain to the left hand side, the sub-base should be formed so that it, too, drains towards the left hand side.

Once laid and compacted, the surface of the sub-base should be reasonably smooth and level, with no high spots or hollows, and accurate to around ±10mm in terms of level.

Base:
The base, as mentioned, is the layer that provides strength. For pedestrian pavements, a depth of 100mm will be adequate. A layer of 10 Newton concrete (can be ordered as readymix) is placed and levelled over a Damp Proof Membrane of heavy duty polythene.

The concrete is spread using shovels and rakes, then tamped down level using a long timber board or plank. The surface does not need to be perfectly smooth: in fact, it’s better left slightly rough as this will provide more of a key for the mortar bed.

The concrete base should extend at least 100mm beyond the planned area of paving to allow for haunching, and any areas of more than 20 square metres should be sub-divided to prevent cracking and movement. This sub-division can be created by placing strips of compressible fibre board (Flexcell) at the edges of each sub-division. The fibreboard can be left in place as it will not adversely affect the pavement structure. Its compressible nature allows each sub-division to move slightly relative to its neighbours without causing cracks.

Remember that the concrete base should have the same profile as the completed pavement and the finished level should be accurate to around ± 6mm. The pavers can be laid over the base as soon as it is in place or work can be suspended until the base is firm and hard (usually 24 hours or more). Concrete left for more than about a week before paving may need to be ‘etched’ using a special “etching fluid” (hydrochloric acid) to remove laitence and create a new, clean surface to which the mortar can adhere.

Bedding:
The clay pavers need to be laid onto a bed of mortar that is roughly 10-20mm in depth. It is bad practice to lay the clay pavers on a bed that is more than 20mm in depth, so it is essential that the concrete base constructed previously is reasonably accurate for level and falls.

The mortar needs to be a good quality mix, comprising 3 parts sand to 1 part cement (or 9 sand to 1 lime to 2 cement). Use a plasticiser when mixing the mortar to make it more workable. The slump (wetness) of the mortar can be varied to suit the preferences of the person laying the pavers. Some installers prefer a stiff, barely damp mortar which contains just enough water to bind together the sand and cement, while others prefer a more fluid ‘bricklaying’ consistency that squeezes out when pavers are pressed down into it. Very wet mortars are best avoided as they are messy and can cause problems with efflorescence in the completed pavement.

It’s often easiest to construct the edge courses first, as these can then act as level guides for the infill paving. Before laying any pavers, decide how the paving will be jointed. The traditional finish uses mortar filled joints, but some DIYers find this can be messy and time consuming, and so they opt to use a polymeric jointing product. The two options are discussed in more detail later in this article.

Working from the unpaved base (not from the newly laid paving!) the mortar should be spread over an area to be paved, but only put out as much mortar as can be paved in 20-30 minutes. If working in courses, put out mortar for just one course at a time, or if laying a more complex pattern, such as herringbone, spread roughly 1m? and make sure you can reach to place and level the pavers.

Use a trowel to spread the mortar roughly 20mm deep, rippling the bed to make it easier to settle the pavers to the required level. Use taut string lines stretched from one edge to the other as guides to the correct line and level.

If you will be creating traditional mortar joints, the abutting edges of the paver to be laid will need to be “buttered” with mortar prior to being placed. This involves trowelling a generous portion of mortar onto those abutting edges. Having a mortar mixed with a plasticiser will help ensure the butter mortar sticks to the edges of the paver until it is tapped down into position.

Offer the buttered paver into position. The paver should be gently pressed against the receiving edges until the butter mortar just starts to be squeezed out, and then lowered carefully into position on the bed. This can be tricky at first, and requires a deal of care to prevent messy mortar staining, but it gets easier with practice.

When using a polymeric, the edges of the pavers do not need to be buttered. The joints will be filled with the jointing material on completion.

Use a small rubber or wooden mallet to tap down the paver to the correct line and level as indicated by the string line guide. If using mortared joints the trowel should be used to remove any surplus mortar that is squeezed out of the joint. Any joints that remain under-filled can be topped up later. Any mortar stains should be wiped off the surface of the pavers *immediately* using a damp cloth or sponge.

Use a spirit level or straightedge to ensure the pavers are draining in the desired direction and that they are even over the tops. Once the mortar hardens, any ‘adjustments’ will be much harder to effect, so try to make sure lines and levels are correct while the mortar is still fresh.

Jointing:
Mortar jointing needs to be completed within 4 hours of the pavers being laid. Due to the risk of disturbing freshly laid pavers if they are walked upon, most installers will top-up any under-filled joints while they are still within reach from the working face. Additional mortar is fed into the joints from the edge of a trowel, pushing it down into the empty joint using a smaller pointing trowel, and removing any surplus before ‘striking’ the joint. This involves using a pointing bar or the edge of a trowel blade to smooth the top of the mortar joint.

Once ‘struck’ the freshly laid and jointed paving should be protected from any foot traffic for at least 48 hours to allow the mortar to cure sufficiently.

Polymeric jointing uses a mix of selected sand and resin to fill the joints without staining the surface. Most of the pedestrian grade polymeric products involve nothing more complex than emptying the pack contents onto the surface and brushing it into the empty joints where it sets hard within an hour or two. It is essential that ALL of the polymeric jointing material is brushed off the surface of the pavers otherwise it will cure and be stuck there permanently.

Polymerics are more expensive than traditional sand and cement mortars but many DIYers and a growing number of contractors realise that they enable much faster jointing, with no risk of staining and an ability to open to foot traffic in as little as 2 hours. Rather than being required to catch up with jointing every few hours, polymeric jointing allows the installer to concentrate on laying all of the paving and then completing all of the jointing in one single session, and in one uniform colour.

Granite is rapidly becoming one of the most popular paving materials due to its inherent beauty, the range of light-fast and natural colours, and its superb durability for all levels of traffic.

For hundreds of years, masons have toiled to dress earth-hewn granite into blocks of a manageable size and to then lay the hard-won rock to create paths, courtyards and pavements that have lasted for centuries. Now, Global Stone have removed much of the hard work and developed a granite paver that provides DIYers and Contractors alike a simple way to put top quality granite paving on any driveway or patio for little more than the cost of concrete blocks.

The key to success when using Polar Granite pavers lies in the preparation. The ground has to be prepared correctly, the sub-layers constructed with care and integrity, and then the granite pavers will complete the project, creating a surface that will gives years of faultless service and great looks.

The area to be paved will need to be excavated to a depth of 200-250mm below finished paving level, removing all vegetation and topsoil in the process and exposing a firm and stable sub-grade (the bare ground).

Over this lies the sub-base, a layer of crushed rock or hardcore that gives the completed paving its strength and ability to carry both foot traffic and family cars.

The best material to use for a sub-base is known as Type 1 (DTp1, MoT1) and is readily available through Global Stone. It needs to be put down as a layer at least 100mm deep (150mm deep for larger cars, vans and 4x4s) and thoroughly compacted using a vibrating plate compactor or roller (which can be hired).

This method of construction requires the uppermost layers (the bed and the pavers) to be reasonably consistent in depth, and therefore it is important that the sub-base layer is laid to a profile that will match that of the completed pavement. So, if the pavers will drain to the left hand side, the sub-base should be formed so that it, too, drains towards the left hand side.

Once laid and compacted, the surface of the sub-base should be reasonably smooth and level, with no high spots or hollows, and accurate to around ±10mm in terms of level.

Edge courses:
This method of building a patio or driveway, known as ‘flexible construction’, works by containing most of the paving within firm boundaries that prevent the paving from moving. On many driveways and patios there will be solid structures such as walls that can be used to ‘restrain’ the main body of the paving, but in other areas, adjacent to lawns, gardens, or weaker structures such as fences, it is necessary to construct “restraining edge courses”, and to maintain a look of uniformity, these restraining edge courses are usually extended alongside walls and buildings where they aren’t actually necessary to ‘restrain’ the paving.

Restraining edge courses must be robust and able to contain the weight of the paving, plus the weight of any users and vehicles, plus the forces generated by those users (acceleration, deceleration and turning of vehicles, for example). Therefore they are laid on and haunched (supported) with concrete. A course or two of pavers are laid onto a bed of concrete (10 Newtons of 1:3:6 mix) using a taut string line as a guide to level and to alignment, and then tapped down to the required level using a small rubber mallet. Once the alignment and the level are correct, the pavers at free edges (not against walls or buildings) can be haunched in position with additional concrete to ensure they cannot move.

Laying course:
Once the edge courses are in place, the laying course can be prepared. This can be thought of as a bed for the pavers.

The laying course consists of a gritty, free draining sand. It is not the same sand as is used to make mortar, but is much coarser and free from any mud or clay. Global Stone will be able to provide a suitable sand for use as laying course for Polar Granite pavers. There is NO CEMENT added to this laying course sand. The sand needs to remain ‘unbound’ (not cemented) and free-draining. Once the paving is completed, it will not move anywhere.

The laying course needs to be 25 to 40mm thick when compacted. Spread sand over the area to be paved and roughly level it out so that it is approximately 30mm below the finished paving level. The sand is then lightly compacted using a vibrating plate compactor (available to hire locally), making one, or at most two passes over the whole area. At this stage, the sand needs to be reasonably compact, but not overly so, because there needs to be some ‘give’ remaining to allow the pavers to be bedded in.

Once compacted, the sand is ‘screeded’, or scraped off to a smooth and even finish. This is usually done using a long, straight board, with a notch cut from the end to suit the depth of the pavers. Global Stone Polar Granite pavers are accurately cut to be 50mm thick, so the screed level will need to be approximately 42-44mm below finished paving level to allow for the pavers to bed-in.

Laying the pavers:
Always start laying pavers at the bottom of any slope, working uphill, and choose a long, straight line to act as a ‘baseline’. This will make it easier to align the pavers accurately and ensure the chosen pattern looks perfect.

There are three basic patterns that can be used with Polar Granite pavers. Herringbone is the best choices for areas that will be subjected to vehicles. Coursed pattern can be used for vehicle areas if herringbone is undesirable for some reason, and it is also ideal for paths and patios. Basketweave should only really be used for pedestrian areas.

Work from areas already paved – don’t stand or walk on the screeded sand laying course as this will disturb the careful levelling and compaction. Lay the pavers ‘hand tight’. This means they can be slightly loose, with 2-5mm between adjacent blocks. There is no need for them to be laid ‘tight-jointed’, as the jointing sand will fill the gaps and will actually improve the strength of the completed paving.

Keeps checking the pavers for level and alignment, using taut string lines as a guide. Lay all the full pavers first, covering as much of the ground as is possible before falling back to cut-in around the edges and elsewhere. Polar Granite pavers are best cut with a diamond-blade chop saw, fitted with a water-spray dust suppressor. Gaps or joints between cut pavers and any edges should not be greater than 5mm. Try to avoid using very small pieces as far as possible.

Jointing:
Flexible construction uses a specially selected kiln-dried sand to fill the joints. As with the laying course, there is no cement used in the jointing. The interlock between individual grains of sand, and between the sand and the pavers will be adequate to ensure the pavers do not move and that the completed pavement is capable of carrying traffic.

Choose a dry day. Empty a bag of the jointing sand onto the pavement surface and use a soft brush to sweep it into the empty joints. Each 25kg bag of jointing sand will cover approximately 8-10 square metres of Polar Granite pavers.

When all the joints are full, sweep any surplus sand into a corner. It will be needed again shortly. The vibrating plate compactor is now used once more, passing over the entire pavement surface two or three times, levelling out any unevenness in the pavers, bedding them down into the laying course (recall that they were laid 6-8mm proud) and shaking the kiln-dried sand firmly into the joints.

A number of joints will now appear only partially filled, and so the surplus jointing sand swept into a corner earlier can now be brushed back onto the pavement to top-up those ‘hungry’ joints.

Completion:
The pavement can be used by both pedestrians and vehicles immediately. Over the first few weeks it is quite likely that some additional ‘hungry’ joints will appear, and these should be topped up with additional sand, but after 6-8 weeks the joints should be completely full and beginning to self-seal which helps keep the sand in place.