Turf tops

Another variation on the use of earth and turf in walling is to built a turf top on an otherwise standard dry stone wall with a stone filling.

Dry stone walls with a turf or ‘divot’ top are common to parts of Scotland such as the Highlands, Glens and parts of the Borders, although they appear to be rare elsewhere. Their presence is likely to be due mainly to a lack of suitable coping stone. Mica schists, for example, may be unsuitable because the effects of freezing can shatter the stone.

Some Scottish single walls also have, or once had, turf tops. Rainsford-Hannay (1972) quotes the Roxburgh Agricultural Survey of 1798 as recommending a layer of turves on top of the wall, placed on edge and ‘condensed together’ with a spade. Although this specific method seems to have fallen into disuse, there are two similar methods still used today.

Both methods are referred to as ‘one up, one down’. The ‘double turf’ is the more usual method, whilst the second method uses ‘one up, one down’ to create a dome.

Double turf

A layer of turves is placed ‘grass down’ on top of the wall, with a layer placed ‘grass up’ on top of this. The inverted lower turf rots down and provides a base for the top layer to root into. In the initial stages, the lower turf also stops soil from falling down into the wall. If wet soil freezes inside the wall it will expand and may hasten collapse of the wall. Once the turf top is established, the mat of roots should prevent any soil falling through.

Cutting the turves

1. The turf should have a good root stock. If it is cut from a field which has been reseeded within about five years, the turf tends to crumble.
2. The turf should be cut about 1-2″ (25-50mm) wider than the top width of the wall, to ensure that the wall is covered. The extra allows for any shrinkage of the turf, or initial dying off of the edges due to drying out.
3. The length of the turf is largely immaterial, although around 8-9″ (200-230mm) is a reasonably effective and efficient size to use.
4. The turf should be thick enough to have good roots, but not so thick that it is heavy to handle, with about 3-4″ (75-100mm) usually suitable. If the soil is very thin and stony you may have to settle for a thinner turf.
5. The turves should be cut to a diamond or parallelogram shape. This ensures a good overlapping of turves when they are placed on the wall, so they bind together well.

Laying the turves

Place the turves tightly up to their neighbours to reduce the chance of drying out. Press the second layer tightly down on top. Some wallers walk on the turf top, or hit the turves with a spade, to ensure good bedding.

Work on short sections of 5-10m as the wall is completed, rather than leaving long lengths of wall to be done in one go. This breaks up the hard and monotonous task of digging the turf.

Domed turf

This method uses less turf and avoids leaving exposed edges.

1. Cut some turves as described above, but narrower, so they are about half the width of the top of the wall.
2. Place these turves grass down along the centre of the top of the wall, covering the hearting.
3. Cut the next layer of turves 4-6″ (100-150mm) wider than the top width of the wall.
4. Place these grass up across the wall, creating a dome over the first layer. Firmly compact the turves, especially at the edges.

When the walls were originally built, the cutting of the foundation trench would probably have supplied sufficient turf for a domed top, without having to dig any extra.

Heather

Heather is occasionally used as a substitute for turf. The process is essentially the same, bearing in mind the following:

1. Heather cutting is more difficult because of the thicker, woody roots. The bases of the turves or ‘divots’ are consequently less regular and usually need to be trimmed square before they can be used.
2. The divots need to be about 6″ (150mm) thick, as they compact more than grass turves.
3. Heather divots dry out quickly, so each one needs to be squeezed sideways into place to reduce the amount of shrinkage.

Further considerations

1. Turf tops go acid very quickly, primarily due to the very free drainage, and mosses and lichens quickly replace the grass. Whilst this non-grass turf still functions as a wall top, it will not be as strong as it lacks the binding roots of grass. Fertiliser, chalk or lime can be added to reduce acidity. In coastal locations seaweed can be sandwiched between the layers during construction of the top, to promote longer term fertility.
2. Turf is normally stripped from a single area of a field. In normal circumstances this will take four or five years to recover, provided there is reasonable depth of soil remaining. The recovery process can be speeded up if the area is filled or covered with organic material, such as compost or silage which has gone off.
3. On wall heads a large stone is placed on top, as in normal coping. This helps prevent the end turf becoming displaced, falling off or drying out.
4. Some wallers place a line of rubble on top of the turf to help hold it in place against cattle and high winds. Sometimes you will find a flat stone every five metres or so between turves. Frequently these would have had iron bars in them for stock proofing and to prevent grazing. If sheep can get at the turf it suffers badly and tends not to last long.
   
5. Sometimes there is a coverband below the turf, as with some forms of stone coping. The reasons for it may include moisture retention in the turf, keeping soil out of the wall, or as a precaution in case the turves degrade.
6. There are examples where a turf top has been used in place of the cover band, below a stone coping.