This section describes paths made of various types of loose stone, laid in one, two or occasionally three layers, and compacted before use. Many different types are available commercially, depending on local availability of natural stone and industrial by-products. Transport is a major cost. Unless a particular source has been used before, material should be checked before purchase, and preferably a short trial section built to determine its suitability. Local materials such as scree, stream deposits and material dug from ‘borrow pits’ near the path can also be used.
The materials act in one of the three following ways:
- ‘Soft’ stone, such as chalk or limestone, which shatters when rolled to form an almost solid surface.
- Stone with clay or minute particles called ‘fines’, which bind when rolled and set to form an almost solid surface. Examples are hoggin and self-setting gravel. Sub-base Type 1 with a high proportion of fines (see table below) will compact with rolling to form a suitable walking surface.
- Material without fines, which should be graded and laid in layers. A useful rule of thumb is that the size of the material should be half that of the available depth.
If material without fines is simply thrown in together, a structurally weak and uneven surface will result.
The highest specification paths have three layers: sub-base, base and surfacing. Whether or not all three layers are needed will depend on the natural sub-grade, drainage, expected use, and the type of material being used to make the path. In many cases only a single layer will be necessary. Asub-base may be needed in very unstable or wet ground, on paths which are liable to flood or for paths which have a very high level of use. In most situations, the bedrock, subsoil or topsoil will be strong enough to support the base and surfacing. The base is the main load-bearing part of the path, and in most jobs will comprise the bulk of the material used. The surfacing provides a surface which should be comfortable to walk on, non-slip and resistant to trampling.
Sub-base material
Sub-base material is used on very rough terrain, to even out the ground, or to provide a load-bearing base for a path over soft ground.
Local stone
Where available near the path, large stones can be used to provide a sub-base for heavily trampled or wet sections, which are then topped by stone aggregate or stone pitching. This is only successful on a mineral sub-grade, and is not suitable for use over peat, as the stone will merely sink into the peat. This technique should be used where it will raise the path above the water table, or to even out rough paths that are appropriate for upgrading and making more accessible for all walkers.
Commercial supplies
Commercial supplies of stone or hard-core for sub-base use are not usually needed for footpath work, as this provides a greater load-bearing capacity than is necessary. However, for particular locations this may be necessary, or for paths which have occasional vehicle use. Access for lorry, dumper or powered wheelbarrow, or a helicopter airlift is essential in order to move the material. For supplies, contact ‘Sand and Gravel Suppliers’ listed in local Yellow Pages, or contact your highway authority for advice.
Building rubble can be used for sub-base material, as it is strong and free-draining. It should be used with caution on acidic sites because leaching of lime from mortar may locally alter the pH. Some sites may have redundant buildings, hard-standings and so on, which can be usefully demolished to provide hardcore. Building rubble is an unsightly material and is best used on excavated paths, where it can be covered with an adequate layer of base and surfacing, and there is no chance of it becoming exposed by use. When laying, very large blocks of concrete or brickwork should be broken down if possible, to make a reasonably even-sized material, otherwise the larger lumps will become exposed with use as material over it will not bind sufficiently.
Geotextiles
Geotextiles are membranes used in civil engineering, which can be used for the sub-base for paths over soft ground and peat. For further details see here.
Base and surfacing – local materials
This describes materials which are obtained on site or nearby. They have the advantage of being ‘natural’ to the site, and of a colour and texture which should blend well with the landscape. They are also free. However, these advantages need to be balanced against the time taken to gather or dig the material, and any adverse effects of this action on the site. Other factors to be taken into account include the amount required and ease of access.
Streams
Material from ‘young’ or upland streams is often suitable as the stones are still angular and have not yet been rounded by the action of water. Shovel material from the edge of the water or from shallow pools into buckets, and lay it without grading. The fine sediment should bind the angular stones as the material is packed down. Old buckets with holes are useful for this job as they save carrying water unnecessarily. Beware of taking so much from one place that the course of the stream is altered.
Outwash deposits
Outwash deposits are a good source of material, and are usually conveniently graded during deposition. Carefully shovel up and lay the material in layers, starting with the coarsest and finishing with the finest.
Scree
Scree material is very angular, and is suitable for the base course. It is usually washed clean of any fine sediment, and must therefore be graded and laid in layers.
Screens for grading surfacing material can be made out of galvanised Weldmesh or similar, nailed to a wooden frame. Revolving drum screens can also be used.
Borrow pits
A traditional method of gaining material for path construction was to dig ‘borrow pits’. These were small pits or quarries dug at intervals along the route of a track to provide suitable material for sub-base, base and surfacing. Borrow pits still have a use in some locations. They are the traditional method of supplying material for stalkers’ paths in the uplands of Scotland. Old trackside quarries, now revegetated, are themselves valuable habitats.
Pathcraft Ltd., working in Scotland and northern England, use the technique of digging borrow pits to provide surfacing material. The location of the pit is chosen by careful inspection of the ground near to the path, and then by sinking a crowbar into the peat to find where there are stony deposits near the surface. The material is then dug out using a crowbar, pick and shovel, and moved in buckets or by power carrier to the path. Depending on the depth of the stony deposits, the pit may be about 1m square and up to 1m deep. For safety reasons, pits must not be dug deeper than 1m, and no ‘tunnelling’ should be done. In suitable material, the sides of the pit should be stable, as any liability to slump would indicate that the material was unsuitable for surfacing. When ‘worked out’, the pit is backfilled with excess rocks from the path, and covered with peat and clumps of vegetation. Within a few days, the site of the pit should be hard to spot. Other borrow pits are dug as necessary for other sections of path.
This method of working is cost-effective on remote Scottish sites, and for the sensitive and detailed type of path construction which these sites require. The natural variety in locally-won material means that the path has a very natural look and feel, as opposed to a path constructed of a standardised material.
Large estates may have their own deposits of gravel or other suitable material which can be dug and used for path construction. In some areas old quarry workings or spoil from various industrial developments may provide material. For the climbers’ path to Allt a Mhuiling, near Fort William, Pathcraft Ltd. used material that had been removed over the years from the inlet of a water pipe to a smelter, and which effectively provided a convenient stockpile of material.
Base and surfacing – commercial supplies
Crushed stone
The type depends on local availability, and names and suitability for paths vary.
Crushed stone can be bought to Department of Transport specifications. The Type 1 sub-base should be suitable for the base layer, and depending on the type of top surface required, can be put down as a single layer to form the surfacing as well. The size of Type 1 stone is 75mm and smaller, about 25% of which is ‘fines’, or dust. The maximum depth required would normally be 200mm of uncompressed stone, which is then compacted with a pedestrian vibrating roller or plate.
Where a smoother surface is required, Type 1 can be laid 100-150mm deep for the base layer, and then covered with a surfacing layer 50mm thick of ‘fines’, ‘dust’, ‘blindings’ or other material sized about 6mm down to dust.
Inspect the material before purchase. The base material and surfacing should be of a colour which blends with the surroundings where it will be used. Limestone aggregates should not be used on acidic soils as water leaching through it may locally raise the pH and alter the flora.
Department of Transport specification for sub-base Type 1
| BS sieve size | % by mass passing |
|---|---|
| 75mm | 100 |
| 37.5mm | 85-100 |
| 10mm | 40-70 |
| 5mm | 25-45 |
| 600µ | 8-22 |
| 75µ | 0-10 |
Quarry bottoms
This is the waste material from the quarry bottom and is the cheapest type of quarried stone. It is obviously very variable, but should contain a lot of fine sediment and will bind without grading.
Hoggin and self-setting gravels
These are gravels with a high clay content that bind when rolled to form a very hard surface. Hoggin is mainly available in south-east England. Some hoggin is of an orange colour which may not be suitable in some surroundings. These gravels are often used for both base and surfacing, and for best results should be rolled several times with a vibrating roller or plate.
A total depth of 100mm for base plus surfacing should be sufficient for footpaths, and would normally be laid directly onto the soil or subsoil if well drained. Poorly drained areas or bridleways will need a sub-base of hard core or stone. Hoggin is not permeable, and should be laid with a camber or cross-fall. A final dressing of pea gravel rolled in will protect the surface against scuffing.
Stone as-dug
This usually contains clay or subsoil.Always inspect before purchase.
Planings and scalpings
This is the material recovered from roads during resurfacing work. It is effective as it binds well, and can be used for the base course, then surfaced with limestone dust. Its origin is not always immediately noticeable, and it can be effectively used in urban-fringe woodland, country parks and other intensively used sites. Although there is no evidence of any environmental damage from phenol leaching out of recycled bituminous material, it should not be used on ecologically sensitive sites. It is a useful material for surfacing bridleways and other riding tracks (British Horse Society, 1995).
Industrial waste products
Basic slag is a waste product from steel works, and makes a good base or surfacing material. It is usually available in 20mm to dust, and should be laid and rolled over a firm sub-base.
Railway ballast
Many old railway lines are now being opened as footpaths and bridleways. In some cases the ballast has been removed, leaving an artificial sub-base which is usually free draining and should support a good grass cover if there is sufficient light. If the ballast is still in place, it is likely to be loose and uncomfortable to walk on, and needs a surfacing of clinker or crushed stone of about 20mm to dust well rolled in.
Stone to avoid
Pea gravel, washed gravel and road chippings are not suitable for either base or surfacing. Pea gravel and chippings are too small and angular, and washed gravel too rounded, to form a strong load-bearing base. If used as surfacing the material moves and ‘crunches’ unpleasantly underfoot, and the path will invariably be avoided.
If you have to deal with an unsuccessful path made in this way, the best solution is to scrape up the chippings and stockpile them nearby. Make a new base of hoggin or crushed stone, and use the chippings to dress the surface from time to time.
Chippings or pea gravel may have use just to dress a beaten earth path to reduce formation of mud, but this is not a permanent solution to the problem. Only put down enough to just cover the surface so it gets trodden in. This will have to be maintained frequently.
Seeding
On some paths, particularly in the uplands, coast, downlands and other open areas, it may be desirable to establish a grass sward on a surfaced path. This makes the path look more natural and unobtrusive in the landscape, helps protect the stone surface from erosion by water and trampling, and provides a comfortable walking surface. In other areas, particularly over wet ground, establishment of a grass surface may be undesirable, if growth becomes lush, and narrows the effective walking surface. On some exposed upland or coastal sites, or where use is very high, establishment of a grass sward will not be possible.
Aggregate paths have been successfully seeded in the Yorkshire Dales (Yorkshire Dales National Park, 1993), with vegetation cover reducing path width by as much as 80% in places. Success however is variable, and the factors are not fully understood. Trampling pressure is not always a significant factor as some heavily used paths have had the greatest percentage cover. Seeding is a standard technique on paths in this area, and detailed monitoring is being carried out to establish the factors which affect its success.
By contrast, establishment of trample-resistant vegetation cover on paths in the Peak District has not yet been successful, due possibly to factors of soil type, air quality and the very high trampling pressure.
In many areas a natural sward will gradually regenerate over an aggregate path, by spreading from the edges and through seeding. Given an optimum level of trampling and grazing, this will maintain itself as a trample-resistant sward over the artificial free-draining base. This is an ideal solution which can be achieved! Further advice on seeding is given in Chapter 11 – Erosion control and vegetation restoration.
Maintenance
Most aggregate surfaces will need annual maintenance.
- Note any patches which are often waterlogged, or places where surfacing or base material is washed away. Install culverts or cut-off drains as necessary.
- Replace surfacing or surface dressing as necessary, as it will get worn away with use even on perfectly drained paths.
- Clear any large stones which have been moved onto the path by water, erosion or trampling.
- Replace damaged edgings if they are still required to contain the path material.
- Trampling should keep down weedy growth on the path. Watch out though for creeping thistle, Japanese knotweed and other very persistent weeds which can come up through a substantial depth of stony material. Treat with a herbicide such as glyphosate.
