Type of Paving

Type of Paving

Larger format paving: With larger format paving slabs or flags (name depending on where you live around the UK, as basically the same thing), the need to ensure a uniform bed is obvious and clear, as any voids or highpoints could lead to poor levels, or damage in service. Slabs / flags are generally a nominal 20 – 30mm thick, and the joints are typically 3mmm to 12mm wide. Whilst larger format jointing is important, the ratio of joint surface and volume to paving element is very low, plus any lateral movement or stress on the joints other than overall thermal movement will be limited and this is one of the reasons these should not normally be used for any heavy vehicular trafficked areas.

Smaller format paving: Conversely, with smaller format paving such as setts or cobbles, again these terms are used for the same thing in different regions, though some stone paving purists may regard stone setts as quarried and ‘cut’ natural stone with 6-defined sides, whereas they consider cobbles to be natural, water or otherwise eroded, and therefore generally round edged, larger natural stone pebbles– from whatever original source - although these are also now manufactured mechanically.

To be technically correct and in accordance with BS EN 1342:2001: “…a sett is a dressed block of stone having plan dimensions that are 50-300mm in length, and a thickness of at least 50mm. The length and/or width should not usually be greater than twice the thickness.”

For all of these smaller format types, without restating the obvious, the stone paving elements are much smaller than with the larger format slabs / flags, and historically throughout the UK, the most common stone sett sizes are 100mm x 100mm, 100mm x 200mm, and 200m x 200mm. The other key difference from larger format paving is their much greater thickness. Generally the traditional thicknesses used in the UK’s historic town centres and market squares was from minimum 100mm to more than 200mm deep, and today the modern traffic loads and exposures are much greater, as discussed further below.

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However, because of the natural beauty and almost unlimited design possibility, today natural stone setts are commonly available from as low as minimum 40mm depth, for limited pedestrian traffic areas only, and with depths from 50mm upwards for domestic / limited trafficked areas. It is sometimes said that smaller format paving elements are much easier to lay and bed them into the substructure, than larger flags. However ensuring these are laid to level and that the intended layout pattern is maintained is another thing entirely. In practice the joint widths for sett paving is usually best defined as a minimum 10mm, but may well be more according to the specific sett/cobbles involved, which again is due to the variable dimensions/shapes and profiles of these variable natural stone paving materials.

As a result of these wider joints, often up to 20mm or more in places, the traffic or movement across finished smaller format paved areas will mean that this dynamic loading must be at least partially transferred to the substructure and / or accommodated by the paving joint materials. It is primarily for this reason that the paving jointing materials tensile strength (for flexibility) and e-modulus (for elastic recovery) becomes far more important than the more often quoted compressive strengths of such materials, especially high compressive strength cement based products, where this is not in fact an advantage. Indeed the compressive strength of a paving joint mortar is irrelevant to some extent, provided it is above say 10-15Mpa for any sudden point loadings. As the direct compressive load is all taken directly by the stone paving elements, it is the dynamic loading stresses that are imposed through and to the paving joint mortar. It is also worth noting that whilst each smaller format paving /element sett can be regarded as easier to lay and bed individually, the skills required to lay natural stone setts and cobbles to a high standard such as in these images is very high and requires the best of craftsmen to do it well.

Maybe these are some of the reasons that unfortunately, there is less of this ‘small format’ natural stone paving being seen in new construction today. Yes it can be expensive to buy and install, but professionally laid and jointed in traditional or bespoke patterns, smaller format natural stone sett paving is also just about the toughest. Natural stone sett paving is therefore an incredibly durable form of hard landscaping, with a long and almost maintenance free, extended service life. Natural stone sett paving can accommodate the heaviest types of 40 tonne articulated vehicle traffic and their 8-11.5 tonne axle weight. Hence the reason this format is often used for premises entrances that are used by such heavy trucks and where they are also often turning, accelerating or braking in these areas, as they drive into and out of traffic, thereby imposing their most severe stress loadings in these positions. Jointing with the unique GftK vdw 850, or vdw 855 for the heaviest exposure in these areas is not only the most durable solution, but because of the minimal maintenance other than cleaning as and when required, it is also the most sustainable and the most cost effective when full life-cycle assessment and costing is applied.

Finally, and very importantly of course, a great many people, including the whole team here at NCC, also think that professional natural stone sett paving always looks absolutely superb.

Selecting the right type of paving for your project

Selecting the best options for your paving project may seem easy, but it can be a complex process with many pitfalls, as there are now so many different suppliers and types of paving available. Unfortunately, this means that whilst there is a lot of information out there, there is also a lot of misinformation. As with anything commercial these days it seems, and so it can be easy to get confused: for example, both natural stone and concrete paving can be obtained in different thicknesses from as low as 12 to 18mm e.g. for some porcelain / ceramic tiles that are actually only designed and suitable for internal finishing only, external grade porcelain should always be 20mm thick and not 10mm tiles designed for interior use only. Natural stone paving flags / slabs can vary from nominal 25mm to 35mm thick according to type of stone and intended areas of use.

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The obvious rule and guidance for selecting the best type of paving for any given area and application, is that the softer the paving units and the heavier the exposure, then the higher the thickness of stone you should be using. Equally the higher the loading and exposure severity, then the optimum solutions are likely to be harder, thicker and less permeable paving units. This also follows for smaller format paving and natural stone setts, where today in addition to the traditional 100 to 200mmm thick units, there are also some available from as little as 40 to 60mm thick, but of course these must be strictly limited to domestic patio and driveway type uses. For heavier vehicular traffic any setts should always be more like the old standard stone sett size of a nominal 100mm (4” in old money) thickness. Any thinner than this, then again: Buyer – Beware!

The stone setts and cobbles that have been used and have survived for many years, even since pre-Roman times were minimum 100mm to more than 200mm thick, predominantly granite or other hard local stone (slate, basalt, gneiss, quartzite, limestone etc.) cobbles that have historically been used for surfacing our roads and market squares since pre-Roman times in the UK. Obviously thinner paving stones are lighter, easier to handle and cheaper to install all round, which maybe fine for a patio, but once you are looking at the heavier exposure on even a domestic driveway, thinner slabs, flags and setts will not last long, even with a significant substructure being provided.

Therefore in summary, when considering your paving project, it is always very important to consider the specific exposure and intended use of the finished paved area. This includes the type and frequency of pedestrian and/or vehicular traffic, the maximum weight/loading of the traffic e.g. a car in your driveway weighing from 1-2 tonnes, or larger commercial vehicles weighing up to 11.5 tonne per axle for 40 tonne articulated trucks (the largest and heaviest generally allowed on UK roads). Each type comes with its own advantages and disadvantages. Understanding the major attributes of every category will help you in picking the perfect option, which matches your requirements and budget.

There is a lot of useful advice on the UK’s only fully independent source of natural stone and concrete paving here www.pavingexpert.com. Please follow the links on the left of this page for a brief summary of the different types of natural stone and paving elements available in the UK and from which to select the best option(s) for your paving project.

Also it should almost go without saying: if you are going to use a good quality paving, especially with expensive natural stone, why would you want to leave the jointing to chance and hope for luck and buy the cheapest product you can find on the merchants shelf or online! It would make absolutely no sense at all, nor would leaving it to your contractor to select. Any contractor is primarily interested in how easily and quickly they can do the job and of course, get paid. The key criteria for many contractors, especially general builders,in selecting a jointing material are going to be:

Cost per Kilo / Litre / Tub, Availability and Ease of Use

Whereas the key decision-making criteria for paving Owners and Specifiers are generally somewhat different, namely:

Overall Cost of the Installed Jointing, Waiting Time Before Use, Durability and Ease of Cleaning, Aesthetic Appearance

Therefore, when selecting the best type of paving, always be sure to also select the most appropriate paving jointing material and normally this should be a specific product – Paving Stone and Paving Jointing are both very much ‘Horses for Courses’ and so there is no overall, one-size-fits-all solution to paving jointing. Even on the same project different solutions may be required e.g. for different sized joints or traffic etc.

So once again, and as always - Buyer Beware!

For more advice or assistance with your specific paving project, and any aspect of paving jointing, please call 01257 266696 for FREE Expert Advice during normal office hours, or you can email at: sales@nccstreetscape.co.uk and we will get back to you just as soon as we can. Thank you.