Preparing the ground when laying granite setts

Laying Granite Setts

Laying granite setts correctly can provide an enduring and attractive look for years to come, in both contemporary and traditional settings. Although some designs that involve complicated and intricate patterns are not for the faint-hearted, and may well be better executed by experienced professionals, many applications are well within the skill set of the competent DIY enthusiast. The basic principles are the same to follow regardless of the size or nature of the project. Follow the relatively simple steps listed below you can create something that not only you can be proud of, but future generations can enjoy as well.

The Laying Process

  • Select a level area that is firm and well-drained
  • Lay a sub base to a depth of between 100-150mm deep
  • Thoroughly compact the area with a plate vibrator or roller
  • Lay the setts on a mortar base up to 30mm thick, three parts sharp sand to one part cement
  • Position the granite setts a finger-width apart or as required
  • Bed the granite setts down firmly as required with a suitable hammer or rubber mallet
  • When dry, fill the joints with a workable mortar using a pointing trowel
laying granite setts around a fire pit

Preparing The Ground

The exact depth of the sub-base may vary depending on the ground. Virgin ground that was previously been used as a lawn, for example, will require a greater depth of sub-base material to ensure that there will be no movement as the ground settles. The granite setts themselves will not crack, split or shatter and will only move if the ground on which they are laid has not been adequately prepared.

mortar moisture when laying granite setts

Mortar base for laying the granite setts

It’s important to lay the setts on a mortar base that will allow for the variations that exist in natural split granite. A mixture that has too high a moisture content may become problematic when tapping the setts into place. When agitated, moisture in the mortar will rise to the surface, and although the setts will bind to the cement-based mixture perfectly well it may become difficult to achieve a level finish. We recommend that the mortar should have a stiff consistency to lay the setts, but not be too dry. Some moisture is very important, but it should be workable. In a granite sett that has been produced to be 100x100x100mm in size, there will likely be at least a 10% variation, therefore some of the setts will need firming into place more than others.

Joint sizes

With the variations in the sizing of natural split or tumbled setts, it is advisable that a finger width joint be left between them. These types of natural products are not evenly sawn like a cast block paving stone and therefore laying them without any mortar joint, not only will be next to impossible but will not be aesthetically pleasing and may detract from the overall appearance. If considerable care is taken it is possible to lay the setts very close but not touching. Depending on the laying design it may be useful to follow a string line or straight edge to ensure consistency because the setts are relatively small it’s easy to drift off course slightly, not advisable especially if following a geometric design.

pointing granite setts

Pointing

One of the most frequently asked questions we get asked about is what method to use to point the setts. It is very important to give this issue due consideration. If using the traditional method of pointing with a sand and cement mixture, although the materials will be relatively inexpensive, undertaking this method correctly can be a time-consuming business and have a significant effect on the financial costs of the project. As with the consistency of the mortar used for laying the setts, the moisture content for the pointing is also very important. Too wet and you may be in danger of staining the granite, which although it may be possible to clean afterwards, can ruin a lot of the hard work involved in laying them in the first place. If the mixture is too dry and is simply brushed into the joints the chances are that in time, as it may not have been compacted well enough into the cavity it will fall through and require attention in the not too distant future and turn out to be unsatisfactory. I’m afraid that if you intend to go down the traditional route, there is no real substitute for taking your time and slowly filling the joints with a workable mortar that can be smoothed over with a pointing bar or another such tool.

Suggested Design Patterns

Coursed

Probably the most widely used style seen within the towns and cities of the British Isles, the courses run adjacent to the flow of traffic normally with a border of setts, two or more wide, framing the courses. Relatively simple to lay, setts of roughly the same size can be layed in continuous courses by using a string line to ensure they remain parallel, taking care to stagger the joints. Often this style can be seen with a slight camber which enhances the look and helps guide rainfall towards the drainage channels.

Random

As the name suggests this style of laying the setts does not necessarily follow a set pattern, cobbles or setts of different sizes can be laid side by side trying to ensure that the jointing gaps are staggered where possible or at least are kept to a minimum, which in turn will help with the final look achieved. This type of work executed well can give a wonderful effect but it can be difficult to avoid oversized joints, which will detract from the finished appearance. If the material used is of a particularly random sizing, framing the area with a more uniform size of product can make the overall effect stunning.

Fan Design

Arguably the most complicated design to lay out and commonly seen throughout mainland Europe.The Fan pattern creates a visually stunning appearance but will only work well when the setts used are the smaller setts. This type of design requires a reasonably large area and will not look so impressive on for example a narrow garden pathway, where the fan patterns can get lost, as it will on a wider driveway or courtyard setting, where the repeating design can be seen to full effect. This pattern can be enhanced by adding different coloured setts on the archway sections to accentuate the fan. Not for the faint hearted, laying out the fan patterns accurately using a wooden form or template will ensure that the same radius is repeated throughout which is essential to the finished effect.

Bogens

Differing from the fan design in that these patterns are a series of interlocking dome shaped arcs, generally characterised by the setts at the outer limits of the dome needing to be slightly smaller than the setts used at top of the dome shape, where one arc meets the other. Not as geometric in design as the fan this type of work needs to be undertaken by an experienced professional. Over a large area, where one arc flows into another this style of work looks fantastic and although it can be seen in some civic areas within the UK, it remains more popular in continental Europe.

Frequently Asked Questions

How deep should my sub-base be?

The depth of the sub base could vary to some degree depending on the ground conditions, but as a rule somewhere between 100-150mm should be adequate. This will then need compacting thoroughly using a plate compactor or roller.

What materials should I use for a sub-base?

A stone based aggregate containing anything from 40mm down to dust will be perfect for laying granite setts.

How wide do the joints need to be when laying granite setts?

This is down to personal preference however find a finger width joint to be a good guide. Joints that are too wide tend to look a little untidy however if the product is a natural split or cleft granite sett, there will be variations in the sizes so attempting to lay them too close together may be problematic.

When laying granite setts, what consistency should the mortar be?

In short, the answer is not too wet but definitely not too dry. There needs to be some give in the mortar as the setts will need tapping into place. If the consistency is too wet then it will be difficult to achieve a level finish, as the moisture content will rise to the surface as the mixture is agitated.

What ratio should the mortar be made to when laying granite setts?

We tend to use a ratio of around three parts sand to one part cement but four parts sand to one part cement would also be perfectly adequate. We normally opt for a sand that has some aggregate content such as a sharp sand but even a grit sand will do the job well. This will give the mortar more structural integrity. SBR is an excellent product sold at any DIY store or builders merchants, this has a number of attributes including being a strengthening and bonding agent and is always a welcome addition to any mortar mix.