Amongst wallers there is considerable debate as to whether the topstones should be placed on the true vertical, sloping uphill or sloping downhill.
Most written sources suggest that sloping uphill is best, arguing that topstones tilted uphill bind most strongly, because as the wall settles they are pulled more tightly together and held by friction. If one stone is dislodged its uphill neighbours stay firmly in place. With downhill sloping topstones, if one is displaced all the others above it are liable to fall in turn.
The downhill argument maintains that it is not practical to place stones leaning uphill, because if you start at the bottom of the slope you have to hold each stone whilst placing the next one. If you start from the top, the stones loosen and slip away from you.
If you start at the bottom and work up, placing the stones sloping downhill, all the stones place weight on each other, forming a very solid top. If any topstones get dislodged or a section of wall collapses, only one or two stones should fall flat which should then stop those above from toppling. This is probably the most widespread method of coping on slopes, although it’s not clear whether this is because it’s structurally more sound, or because it’s easier to do.
Technically, vertical coping should be the most stable as the weight is perpendicular, but its use is rare on slopes. The ‘uphill’ protagonists tend to use vertical coping on very steep slopes, where there is not enough surface for tilted topstones to grip properly.
A useful tip when rebuilding or gapping a section of wall on a slope with downhill sloping topstones is to rope the topstones on the section uphill of the repair. Rope a fairly long section, of about 16′ (5m) or more, and ensure the rope is tight. Remove the rope when the repair is complete, allowing the bottom stone of the roped section to shift slightly to close the gap left by the rope.
One rare, but nevertheless interesting method of helping to stabilise the coping on walls is to include long stones in the wall which project and hold the coping in place.
Slab copes and coverbands
Occasionally you will find a slab cope used on a slope. The slabs are always set to a true level, with various methods used to achieve this. One method is as follows:
- Set a line to give the final height of the wall, including the slabs.
- Place each stone so that the top corner at the downhill end touches the line.
- Butt the next stone up against it. On steeper slopes, or with very thin slabs, you may have to build a layer or two on top of one slab in order to gain sufficient height for the next slab to reach the line. On steeper slopes the step between slabs might be quite large, so that an additional stone or rubble might be needed to even out the finished line of the top, either to improve its appearance or to make it stockproof.
The use of coverstones on slopes follows the points above, with the subsequent topstones graded in height to create a relatively uniform top.
On steeper slopes this becomes more difficult, as the step becomes too big to easily even out with graded topstones.
Garden walls or those which do not have to be stockproof can be built with a stepped top, by constructing a series of partial heads. This works best with fairly regular, slab-shaped stone, and looks more appropriate in urban rather than rural settings.
