Home & People Dry walling can be as durable as bonded materials

Press, 21 August 1979, Page 12

Home & People Dry walling can be as durable as bonded materials

Stone walls have been in use in Canterbury since the very' early days of settlement. There are' 1 some fine examples of stone walling to be found in the Lyttelton area, as well as throughout Cashmere and many other parts of the Port Hills.

Many of these walls were constructed without mortar, particularly the very early walls.

In the hills area rocks were quarried or cleared from the lands surface to be used in the walls. On the plains smaller stones were used, the rounder river-worn stones and field stones being used in the construction of unusual dry walls.

These early walls and many of the present day walls are excellent examples of the stone walls’ attractions — they are durable, solid and part of the landscape from which they have been derived. Quarried stone was often, used by the more "wealthy early settlers, the stone often being quarried

bn the property ; itself. Stone walls, even in those early dayS, were relatively expensive; they were timeconsuming to build, as they still are today. There are basically four types of stone wall: Field stone, using any irregular shaped, unquarried stone found in or ori the ground. Rubble, using the broken residue from a stonesawing operation. Flagstone, derived from stone which has been so evenly stratified that it splits naturally into flat pieces (Halswell stone). Cut stone, which has been shaped and dressed with a saw or chisel (Oamaru limestone). Stone masonry is separated into rubble and ashlar walls. A rubble wall is constructed from blocks of stone which have been either roughly dressed or not dressed at all and have wide joints. The stone may be split, however, to give a flat face for the wall. It can be used in either a drywall or a mortared wall.

The dry wall can be either a low retaining wall or freestanding. Its construction depends entirely upon the forces of gravity and the friction between interlocking stones. An ashlar wall is constructed from blocks of stone which have been carefully cut and dressed,

with narrow and tight fitting joints. The stones are usually of the same height laid in a continuous course. This "regular” course is the opposite of “random ashlar,” where the stones are of various sizes and the effect of a course is not retained. Stone is selected on the basis of appearance, cost, durability and maintenance. In New Zealand the main source of stone mat-

erial is mica shist, volanic scoria rock, Oamaru limestone, and greywacke stone. A stone wall is judged on its colour, texture, and ageing qualities, as well as on the general characteristics of the landscape in which the wall is to be built. . Some stone is more appropriate for a neatly tailored appearance, while other stone lends itself to a more rugged and naturally informal use.

Frost can have a most destructive effect on certain types of stone. Wet weather followed by frost can slowly but surely cause the disintegration and break down of the more porous stone; the builder should therefore be sure that the stone he selects is of a suitable type. Correctly handled and built a stonewall can be a lasting source of interest and enjoyment.