Structure of a dry stone wall

A recent repair of a tumbled down section of dry stone walling is a good reminder of how important it is to have a strong structure to a dry stone wall. Aside from sound foundations and correct wall  batter, or pitch, a common problem to encounter with fallen sections is that the stones are mostly laid  "length on" like bricks rather than placed into the wall for greater strength. This means that in the middle of the wall a  larger space is left having  to be  filled in with more stone rubble infill known as hearting or packing. When the wall is mostly hearting through the centre  and there are also no longer stones, called 'through' stones or tuskers,  placed right the way through, the wall will not stay up long. This is because there is nothing tying the two outer skins of the wall together and it is mostly relying on  the action of  gravity from the wall batter.

Building in this way is not good practice and can be called 'trace walling', however there can also be other reasons. The waller could have only had access to smaller pieces of stone and was making do with the materials to hand or perhaps had limited stone and was making the outer stone go further and using more infill. It may also be that appearance had been prioritised over strength as the longer 'faces' of the stone can give a more regular masonry appearance. A wall can appear well put together on the surface, but not be strongly built.

This means that when a wall comes down and the original has been built in a 'trace walling' way, in order to strengthen it you can expect to have to bring in quite a bit of extra stone. The original wall will not be  a dense structure and once you start turning the stones inwards this means that you will be making the wall more dense, meaning you'll ultimately need more stone. Also. if there are few or no 'through' stones, then you'll need to bring these crucial stones in as well. The waller is always on the look out for 'throughs', which are laid in several alternate  bands in the wall and are very important in holding it all together.

The wall we rebuilt essentially had no 'through' bands as the stone was all smaller pieces. When the stone is smaller, 'throughs' are especially vital. When stripping out a fallen section its necessary to take the wall on either side of the collapse back in a large 'v' to where the wall is sound on either side.

The collapsed section stripped out in a 'v' shape back to sound wall

The rebuild will quickly fade and no one will tell it was ever rebuilt

We brought in a lot of longer stones in order to strengthen the section of wall. The new stone will quickly fade so that it will look very similar to the rest of the wall. The best outcome of repairing a fallen gap or 'gapping' is that no one will notice it has been rebuilt.