Self Binding Gravel Paths & Driveways
The term ‘self-binding gravel’ is widely used in the landscaping industry as meaning a surface
dressing material that is bound in position by means of fine particles of natural material,
usually clay based, laid as a cosmetic and practical ‘veneer’, providing a uniform colour for
use as pathways and driveways.
It contains a clayey/sticky binding material combined with an element of slightly larger microstones, which provide a ‘gritty’ texture to the surface. Most materials are formed of 0 – 4mm
particles, with a relatively high content of a clay-like material which helps to bind the surface
together and create a solid and hard-wearing surface.
There are a number of different self-binders available, including Self-binding hoggin (Romsey
is one example), Cotswold Gold or Golden gravel (often referred to as ‘Royal Parks’ due
to the number of paths and driveways covered in the materials at stately homes across the
country), Breedon gravel and Limestone dust.
CED Limited offer a superb product known as CEDEC, which is formed from different grades
of aggregate, made from quartzite and granite. This may be considered as a recycled product,
whilst the others are ‘natural’ materials, excavated from sites and quarries.
Preparations
All sites will require preparing, as though intending to create a pathway or driveway by
excavating to an appropriate depth, taking the nature of the soil on site into consideration. It
is essential to dig down to ‘solid’ ground, taking care to address any particularly soft areas
and increasing the depth until you are satisfied that the base will be hard enough to support
the weight of the intended or likely traffic.
Compact the ground, using a mechanical vibrating roller or plate, making sufficient passes
to ensure the ground cannot be compacted any further, then cover the site with a non-woven
geotextile membrane to prevent the sub-base material from being pressed into the soil below.
Footpaths should be excavated to a depth of between 150mm and 200mm, whilst driveways will
require a depth of 300 – 400mm, again, dependent on the type of traffic that will use the access,
including oil delivery lorries or dustcarts, both of which may be very heavy when full.
Most situations will require an edging of some sort. This is usually timber, as it is easiest to
fix at various widths, heights and depths, using wooden pegs to secure the timbers in place. As
with any timber touching the ground, it should be suitably preserved and able to meet Class 4
standards (UC4 or HC4, as determined by BS EN 335-1). Distances between pegs will vary
according to the site conditions and configuration of the edging, with curved designs requiring
additional support to prevent warping and stresses within the timber.
Other commonly used edging products are steel, usually corten or similar metal that is graded
to be suitable for in-ground use i.e. non-ferrous and unlikely to be prone to rusting. (All metal
fixings must be rust-proof), brick, concrete edging blocks or kerbs, all designed to prevent
lateral movement of the sub-base and surface material.
Drainage
Drainage is the most important factor in producing self-binding gravel surfaces, to prevent
water from laying on the surface, thereby allowing the material to dry out and remain in a solid
state. A wet surface will not remain compacted, and may be prone to damage by freeze/thaw
action and rainwater degradation. Therefore, the sub-base must be able to drain freely, and
either crushed concrete, crushed sandstone or any other MOT Type 3 grade material should
be laid to a minimum depth of 75mm (footpaths) or 150mm for domestic drives carrying up
to 3.5 tons.
Water must not be allowed to remain trapped within the surface area of the project, even when
free draining materials have been correctly constructed, and care should be taken to ensure
that gaps are left in the edging restraints, if at all possible. (Working between walls or raised
edges will require additional drainage as described below). Better still, ensure that the gravel
is finished slightly above the edging restraints to allow water to drain into flower beds etc. and
not remain laying on the surface.
Laying Self-binding Gravel
Once the sub-base has been thoroughly compacted, with minimum gaps between the
‘fines’ to the surface of the MOT Type 3, spread a thin layer of 15 – 20mm of the
selected surface material using the back of a rake or screeding board – not the teeth of the
rake – as you do not want to separate the fines from the grittier coarse material. The
self-binding material must be laid moist, applying a light drizzle of water if and as necessary.
(Conversely, if over-moist, add some white cement to the layer to help stabilize the
moisture content) Using a plate vibrating machine or roller, compact the first layer
of surface dressing. Apply a second and third layer to a maximum depth of 50mm,
repeating the process of grading, spraying and ‘levelling’ to running levels and
falls across the surface. Once you are satisfied with the appearance and condition
of the works, make another pass with the roller, this time without using the
vibrating option.
The base and final layer should be designed either with a crown or camber – either central to
dispel water to either side, or laterally to one side only dependent on the site. This operation
is to ensure that no water can remain on the surface. Although water will slowly percolate
through the surface and sub-base, excessive water caused by heavy rain must not be allowed
to remain. In some cases, if water is allowed to build up within the pathway, and collects,
becoming a stream, trapped between the edges, the result may be a ‘wash-out’, with water
displacing the self-binding gravel, causing a migration within the surface. This is especially
a problem on sloping sites.
Additional Drainage
Under certain circumstances – either the design calls for an exposed or raised edge to the path
or driveway, or the site is between walls or banks with no possibility of ensuring that water
can be dispersed from the surface – other methods of getting rid of water from laying on the
surface of the self-binding gravel may be required.
Depending on the nature of the site, and especially the type of soil – clay being unlikely to
be free draining – and if the pathway is bounded by raised edges, additional drainage may be
required in the form of a ‘soakaway’ or ‘French-drain’ may be incorporated into the edges of
the path, by excavating a channel to the depth of the sub-base and creating a looser version
of the MOT Type 3 sub-base using more open grade crushed concrete, (with non-woven
geotextile at soil level) topped with pea shingle or gravel, as close to a colour match to the
chosen self-binding gravel. This channel may be between 100mm and 200mm depending on
the site and potential volume of water. (Measure the total surface area likely to be affected)
In some cases, it may be prudent to include a perforated flexible land-drainage pipe into the
drainage channel, leading into a discharge point or crated underground soakaway system, the
size of which will be dictated by the likely volume of water it may have to contend with.
Be aware that such additional drainage will gradually become clogged by fine material
leaching from the self-binding gravel as rainwater moves the particles across the surface. This
will result in a paucity of fines in the surface, which will degrade the efficacy of the drain run.
Maintenance
Self-binding gravels are excellent ‘landscape’ surfaces and well suited to their intended use
– if properly prepared and maintained. There will be visual changes, with the fresh material
altering colour as it becomes weathered. A bright yellow, golden or white finish will become
faded and covered in a ‘film’ of algae, especially on wet or shady sites. I recommend regular
cleaning and removal of leaf material and any surface weed seedlings which are bound to
occur naturally – usually wind-borne – and a light rake with a fine tined wire leaf rake will
bring the grittier particles to the surface, creating a fresh appearance.
If required, additional new material may be introduced as years pass, using the same methods
as the original scheme, and a light treatment with a mechanical roller or vibrating plate will
keep the pathway in good order for many years.
