The basic procedures and considerations of use to consider when laying granite setts; the difference between rigid and flexible types and importance of stone type.
What to consider and how to best proceed when laying granite setts
Setts, also commonly known as cobbles, are a hard wearing, attractive and characterful surface. They’re ideal for driveways and garden paths, and feature heavily in older developments such as stately homes and in older areas of towns and cities containing archetypal ‘cobbled streets’. Laying setts entails following the correct procedures and assessing what demands will be placed on them.
For a light use garden path it should be straightforward, but problems can mount when the aesthetics threaten to get in the way of practicalities.
For example, if laying (or more likely re-laying) setts in a location such as a period property’s courtyard, it could be difficult to recreate the style and look of setts laid two or three centuries before. Back then loads were lighter compared to now when the same setts might have to withstand modern tourist demands such as the weight of coaches, cars and high volumes of foot traffic.
Choosing the right type of granite setts is obviously paramount as is selecting exactly the correct quantity required along with each variety in terms of size and style.
So to the basic steps to take:
The first question to ask is will it be a fixed or flexible system?
Fixed: a compacted sub base which may have a concrete base laid. Onto this the setts are laid and set in a sand and cement mixture.
Flexible: a compacted sub base with the setts laid on top and set in sand only.
You need to consider the drainage fall and the amount of digging required based on the depth of the setts, the optional concrete base layer, and the sub base. If laying setts as far as the outer wall of a building, then the top level will need to be a minimum of 150mm below the damp proof course.
The important layer that bears the overall load placed on the setts, it would typically be around 150mm of aggregate thoroughly compacted with no gaps.
In the case of a rigid system, if a concrete base layer is installed over the base layer it would usually be between 50 and 150mm thick depending on the demands likely to be placed on the finished structure.
This is the layer the setts themselves are supported in; with a flexible setup, it’s basically a layer of sand whereas with a rigid system it’s a mix of sand and cement. The sand itself should be of a coarse, gritty composition in both flexible and rigid applications as ‘normal’ building sand is too soft.
The thickness of the setts will influence how thick the bedding layer should be.
Laying the setts
Laid carefully by hand, each sett requires careful positioning whilst paying attention to the drainage fall and cambers, especially if it’s a road surface.
In a flexible system, you’d brush in jointing sand whereas with rigid setts a dry mixture of some four parts sand to one part cement would be used. In both cases, a soft brush would be used to work the material fully into the joints followed by packing it down with a trowel.
A specific skill
Laying setts is a specific skill, even more so when trying to recreate the types of sett laid many years previously.
It’s also important to specify the correct stone pertaining to the period and location in question, especially if laying setts in a location such as a building or area where historical authenticity is important. All those years ago when setts were first laid the stone would be largely specific to the locality in terms of where it could be easily transported from.
For example, limestone setts sourced largely from the Derbyshire Peak District aren’t usually seen anywhere further than about 20 to 30 miles away from the source of the limestone used, and the dark granites of Snowdonia are mostly restricted to setts laid in areas of North Wales, Lancashire, Cheshire and Staffordshire.