A Guide to Dry Stone Walling

“A Brief Guide to Best Practice and Common Faults”

This page describes some of the general principles of dry stone walling, along with some of the more common faults that can occur. My hope is that this brief guide, and the links to further sources of advice, will help customers develop a productive and transparent relationship with their waller.

For information about the services that I can provide, please visit my dry stone walling services page.

Dry Stone Walling

Stone comes in many, many different shapes and sizes. This gives rise variations in walling styles and practices, which can often be very localised. As wallers we attempt to maximise the benefits of a particular stone type, and mitigate any inherent weaknesses. Despite these differences, there are many common principles which should be followed and will have a big impact on the durability of a wall.

The following information should help you identify the most common problems, and work with your waller to solve them. It’s also worth stressing that much of the strength of a dry stone wall is internal and, therefore, can only really be inspected during construction.

Weight Distribution

diagram showing cross-section through a drystone wall and the most common movement resulting in failure.

Walls are very heavy, but that weight is not uniformly distributed across the wall. This is an inherent design flaw, which good wallers will try to minimise. The image above shows a typical wall in cross-section. The two external faces are built of large, solid stone with little space between the stones; by contrast, the centre is filled with smaller stones relatively large spaces between the stone. Consequently, a typical wall is heavier towards the outside than the middle.

Over time, this difference in weight distribution causes excess load to build up on the front edge of the foundations, which then tilt and sink further into the ground. The stones above, now also tilting and resting on a sloping surface, begin to slide off. This normally occurs on the downslope side of a wall (even if the gradient is very shallow), as soil creep and the natural effects of gravity work harder in that direction.

Through stones help to reduce this settlement by binding the wall together and by evening out the weight of stone above. This latter trait has the effect of diverting the centre of gravity towards the middle of the wall, which in turn helps prevent the foundations from deforming unevenly and greatly increases the lifespan of the wall.

Foundations

diagram showing how to lay foundations for a dry stone wall

Foundations contribute to most of the strength in a wall, and are nearly always a root cause in its failure. In newly built walls, foundations should be large, flat stones set level, and cover as much of the base of the wall as possible (the image opposite shows good and bad foundations). In existing walls, the situation is more complicated.

highly deformed foundations causing collapse of dry stone wall

Where a wall is being rebuilt because of age-related failure, the original footings will likely be deeply buried, heavily sloping and out of line with the wall. The image below gives an example of the conditions often found in existing walls.

Digging out and resetting original foundations is very time consuming, and therefore expensive – but rebuilding a wall on poor foundations WILL result in a less durable wall. It may be worthwhile examining the condition of the foundations at several locations before construction starts, and discussing this with your waller. In some cases, building a smaller wall or adding extra through stones may help offset the problems caused by poor quality footings.

Length into the Wall

problem of weakness caused by trace walling in dry stone walling

Most stones should be placed with there long axis running into the wall. This serves three functions: 1) it distributes the weight of the face of the wall into the centre, which creates a more stable structure; 2) it creates more contact between the face stones, which in turn generates more friction and reduces the effects of seasonal movement; 3) it requires greater leverage to dislodge such stones, meaning the wall will survive in better into old age.

The opposite of this – i.e. running the long axis along the wall – is known as ‘trace walling’. Trace walling is unfortunately very common practice, because it is easier and yields more wall in less time. Excessive trace walling results in an unstable structure, and if combined with other faults, is likely to end in unpredictable large-scale collapses.

Most faults and weaknesses in walling reveal themselves gradually and it will likely become clear that a wall needs repairing well before any potentially dangerous collapse occurs. Trace walling and poor stone contact (described below) differ in that they can result in sudden failure without warning.

N.B. In places with public access this uncertainty could pose significant risks.

Contact between Stones

In common with running stones length into the wall, walling stones should have good contact between one another. Flatter stone types generally have naturally good contact; rounder stones typically require more careful selection to attain sufficient contact. The diagram below shows how the use of a particular stone can affect the strength of the wall and its appearance.

Poor contact between stones caused by attempting to use stone to create attractive walling

Judging the amount of contact acheivable for a given stone type requires experience, and therefore an amount of trust with your waller. As with trace walling, sacrificing good contact is often quicker and can create a more attractive wall, but is structurally very unsound.

Further Information

For guidance on commissioning dry stone walling, particularly for publicly-funded works, I would refer customers to STONEWORK A technical guide to standards and identification of common faults in dry stone walling. Stonework was written by Sean Adcock, one of the foremost wallers in Britain, and explains many of the issues discussed on this page.