The Importance of Permeability

Category: Sureset Blog

Posted 17th May 2012 by Kevin Weston


Commercial and residential specifiers are faced with an ever-widening range of materials to select from for external surfaces.  From concrete to clay and asphalt to resin bound paving, the choice to the uninitiated can be bewildering, with manufacturers keen to promote the specific benefits of their own product ranges.

Increasingly within these lists of product benefits, claims are being made about the permeability performance of different materials, with manufacturers anxious to demonstrate that their products provide the perfect solution for a wide range of applications – whether it be a commercial requirement for a Sustainable Urban Drainage System (SUDS), or a homeowner who wants to avoid standing water forming and lingering on their driveway.

But why has the issue of permeability become such an important one?  In a commercial context, it is largely due to the presence of SUDS requirements and the need for landscape designers to take account of surface water run-off and drainage – the impact that urban development has on local bodies of water. The use of hard landscaping surfaces has a significant bearing on such schemes, particularly the degree to which water is able to drain through the hard surface and the rate at which is does so.

In a residential setting, the issues are much the same.  But the issue for homeowners is more than just about performance – it also has a significant bearing on planning applications, as since 2008, legislation in the UK requires that planning permission must be obtained for any new or re-paving project that is non-permeable.  This is a clear indication that a permeable paving surface, capable of quickly and efficiently removing standing water, provides some important advantages.

A preliminary examination of the main surfacing materials reveals a fairly broad spectrum of permeability performance.  At one extreme concrete and asphalt surfaces are particularly impermeable; water simply sits on the surface and forms puddles – or runs off into surrounding landscaping, depending on the severity of the rainfall.  And at the other extreme are gravel and chippings which allow water to drain through freely.

So gravel provides a permeable surface – and looks good, at least in the immediate days after it has been put down.  But these good looks tend not to last.  After a little trafficking, the stones tend to become dispersed and spill out over other surfaces; weeds can also start to grow through relatively quickly.  They are also very difficult surfaces for users of wheelchairs, bicycles, pushchairs etc to navigate.

There are however other, more modern materials that combine permeability with good looks and durability – one such material being resin bound paving.

As its name suggests, resin-bound paving combines gravel, stone, marble or other aggregate with a resin which completely coats the material and permanently binds it together.  This provides a surface which is completely permeable, allowing water to freely flow through, as well as a long-lasting, low-maintenance surface which will not fade or deteriorate over time; will not allow weeds to grow through and will not allow gravel or other aggregate to become loose and dislodged.  In short a perfect combination of aesthetics and performance.

Leading manufacturers of resin bound paving like SureSet, the market leader in the UK, supply a huge range of colours and textures to choose from to complement or contrast with any style of commercial project, home or garden.  Options include natural gravel and crushed stone, marble and even recycled glass all in a wide range of colours.  From shades of natural buff and brown to rich shades of terracotta and strong primary colours, the palette offers enormous scope to create striking designs.

However, whilst the top material is a vital element of the permeability of the overall surface, the sub-base is also important and care and attention must also be paid to its design and installation.

Materials such as a Type 3 granular sub-base are commonly used, but a sub-surface resin-bound layer may be used to create a sound suitable base for the resin bound paving to be laid upon.

Another alternative is to consider a cellular confinement system, such as Cellweb, the material recommended by SureSet.  Initially developed by the US Army to construct unpaved roads on weak ground, Cellweb is a cellular confinement system incorporating interconnecting cell walls which form a durable composite layer, much like a typical mattress, that can be filled with sub-base materials.

Using this system, the sub-base is constructed within the Cellweb ‘mattress’ using a well compacted Type 3 material, graded and crushed concrete or recycled or secondary aggregates.  Beneath this (and above the sub grade) sits a Cellweb separation fabric, which essentially prevents fine soil particles migrating upwards towards the surface.  This approach ensures that the sub-base is kept completely stable, providing a high-integrity surface on which to lay the resin bound paving.

Manufacturers and experienced installation companies will be happy to offer advice on the most appropriate sub-base needed for each particular application.

Resin bound paving is quick to install, with the low energy material mixed cold on site and hand floated by skilled installers to deliver a perfectly smooth finish.  Manufacturers such as SureSet can provide a full installation service if required, or can recommend approved and fully trained installers to deliver a perfect surface which will provide many years of high quality performance, providing a highly durable, UV-stable surface which is resistant to frost, oil and stains.

Every SureSet project is backed by a comprehensive 15 year guarantee, providing assurance against loose stones; cracking; oil damage; UV degradation; colour change; frost damage and poor workmanship.

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