The Galloway or half-dyke probably developed as the best way to use supplies of stone that were mainly large and medium size, with little hearting. The large stones used in the upper single part would make a very wide wall if used double. It is an efficient walling style, using less stone at any given height than a double wall.
The lower half of a Galloway dyke is built as a standard ‘doubled’ wall, although the stone is often smaller than would occur at this height in other walls, as it comprises all those stones not large enough to build the single.
The single must consist of at least three layers of single to be a true half-dyke. Many Scottish dykes have a thick irregular cover plus level coping, but these are not half-dykes.
Dimensions
According to Rainsford-Hannay (1972) and Prevost (1957), the true Galloway dyke was of the dimensions shown. Prevost gives the finished height as between 5’3″ (1.6m) and 6′ (1.8m), and specifies throughs at 1’9″ (530mm). He contrasts the Galloway dyke with the normal half-dyke, where the doubled section extends to half the wall height.
In practice the Galloway dyke or half-dyke varies in dimension and detail from area to area. The cover-band usually projects by up to 2″ (50mm), with larger projections avoided as cattle rub on them, and any stones of this length should be used as throughs, lower in the wall. A useful rule of thumb is to use the size of the coverband stones to determine the height and width of the double. The double is battered about the same as a standard dry stone wall, at 1:6 to 1:7, or 1″ of batter for every 6-7″ (1cm for every 6-7cm).
The building of the single follows the same principles given above, with a few refinements. Many dykers refer to all of the stones of the single as ‘covers’.
Procedure
Dismantling
The doubling stone is set out on both sides as for a standard wall, and the covers and single stones are set out on one side only. If the double contains throughs it’s usually best to set these out on the opposite side of the wall to the covers and singles, so you don’t muddle them up.
Foundation
Unlike standard walls, the largest stones do not necessarily form the foundation, but are used instead in the single section of the wall, so the foundation stones are often much smaller than normal. Occasionally stones which are too large to be lifted up to the single section are used in the foundation, but if you are rebuilding, all the single stones have to be saved for re-use as singles, unless additional stone is available.
Short line bars are often used for the double, although the irregularity of the single makes them less appropriate higher up.
Hearting and pins
Having sufficient hearting and pins is often a problem with rebuilds, and it’s all too easy to use up all the pins as hearting. Dressing of the singling and coping may produce some usable pins, though rarely enough. It’s not advisable to skimp on hearting, so you are likely to need to bring in some more.
Throughs
Throughs are necessary for higher doubles, and advisable for lower doubles, as the building stones are relatively small for their position in the wall, and anything that helps resist bulging or uneven settlement is helpful.
If the double is over about 20″ (500mm) high, it usually contains projecting throughstones at 36″ (900mm) centres. The double is capped by a coverband on which the single is built.
General points
These points apply to single dykes, half-dykes and Galloway dykes.
Heads
The construction of heads to single walls can be a problem. Care has to be taken to ensure that joints are crossed, although it is often difficult to achieve more than minimal overlapping.
With a Galloway dyke, it may be advisable to sacrifice one or two of the stones from the first layer of covers and use them in the head. Although you may then have to use less suitable stone for one or two covers, it’s more important that the head is really solid.
Another method found in some Galloway dykes is to build a standard wall head, merging this with the rest of the dyke.
Curves
Curves present a problem on single walls. Care must be taken to avoid ‘fanning’ by using complementary shapes, which is easier with more irregular stone. Level bedded stone, such as many sandstones, are too regular and difficult to build to a curve.
Turf top
In areas where turf tops are common, these can be used on single walls. There is no need to level the final layer, but it must be wide enough to take the turf. Some dykers cut the turf about twice the width of the wall top, and then drape the turf over, as this helps prevent drying out and provides a more secure and substantial finish.
Turf tops may need maintenance, as if the turves dry out they will get displaced. Many single walls look as if they are disintegrating, but it is merely that the rough top has become exposed because the turf has gone.
Clashing
The single sections of some Galloway walls in South West Scotland are pointed with mortar or ‘clashed’ after completion, to help prevent cattle damage.
Theoretically the dyke should be left to settle for a year after completion, before the singling is roughly pointed with a 5:1 mix of coarse sand:cement. Tacky mortar is literally thrown into all the gaps and joints, left for half an hour or so until it is just going off, then pushed in and finished with a soft brush.
This can look unsightly at first, although the damp climate means it weathers quickly and has a softer look after 4-5 years.
Regional variations
As with all types of wall, the pattern of singles and Galloways varies from place to place, and the following are just some of the examples which can be found.
Scotland
Here the single is a mix of irregular sandstone lumps and slate, with the use of long slates to help bind the smaller slates. The longer slates would normally be placed first and their bases secured, with subsequent stones forced down into the gaps between them. The use of rounded stone in the upper layers does not work well, as it does not bind with the slate. The single footing is unusual in that most of the stones are set vertically rather than flat.
A very random single, in terms of layers, and also mixes vertical, flat and angled stones. The singles of Strathrusdale contain some impressive boulders, but unfortunately many of the roadside walls are falling into serious disrepair, damaged by snow ploughs piling snow against them, and the raising of the road surface causing drainage problems along the base of the wall.
This single at Laid, Loch Eriboll, contains small ‘pockets’ of doubling, with foundations a mixture of standard double, single and shiners.
This half-dyke in Glen Too has a thin, flat coverband, with a very random single of angular stone.
Incorporating stones from the remains of a broch, this half-dyke in Glen Cassley is thought to be over 150 years old, but the singling is still very solid. The doubling is only 12″ (300mm) high, topped with singling of upright sandstone laid perpendicular to the slope. The half-dyke has very solid heads at the bottom of the slope, built as for standard walls.
A Galloway dyke of whin, with random, angular singling and tilted coping.
The ‘butt and hudd’ style mixes single and double walling in fairly random sections along the wall, according to the stone available.
Rest of Britain
In the rest of Britain, occasional single walls of the type described above can be found in areas where the walling stone tends to boulders. More commonly though, single walls are built with the stone predominantly laid flat, a style which is only rarely found in Scotland.
The problems of sitting ‘flat’ stones solidly in a single are outlined here. The coping is also often weak, as being laid flat, there is no cohesion between the stones.
Singles of large flat stones can be very secure, as seen in the walls on Dartmoor, which has the most extensive area of single walling outside Scotland.
Most of the Dartmoor singles are only three or four stones high, even when 4′ (1.2m) high. Wedges are often used, with the weight of the granite holding them very securely. The cope is less secure, especially where smaller stones are used.
The example below demonstrates amazing craftsmanship, being built of large blocks expertly fitted together and finished to a level top. The largest block, in the top centre, is 5’2″ (1.55m) long, 1’10” (550mm) high, and 1’5″ (420mm) wide, and must weigh almost a tonne. A characteristic of these granite singles is that all the stones are set to give an even face on one side of the wall, with an undulating back face, rather than being set centrally as in the Scottish singles.
Rarely, half-singles are built to a herringbone pattern.
