Rock versus Stone

Rock is unshaped as it naturally occurs in the ground. It is usually blasted, dug up, crushed and screened.
Stones are rocks that have been shaped to allow them to be used in building and dressed to a specific surface treatment by mechanical means as in the case of splitting or guillotining or the elements as in the case of river and field stones.
Stone types common in NZ – schist, limestone, basalt, scoria, metamorphic (eg Hinuera)
Dressing the face of stone can be left natural, split, guillotined, sawn, sandblasted, polished, flattened, tooled with a pattern, or more heavily carved. By hand or machined.

Stacking

Stones that are not held in mortar are called dry stacked. Their structural integrity is dependent on the quality of fitting, pinning, and hearting internal to the wall. The less air gaps and more stone in the wall the more solid and durable it will be.

Dry stacking is the most traditional method of wall construction and good option for properties with suitable nearby stone resources.

Tight Stack

Tight stack is defined as stones fitted with joints less than 10mm. Normally the mortar is racked backed to reduce visibility and simulate stone on stone dry stacking. The tighter the fitting the slower it is to stack. Stone will likely be guillotined (or cut) with flat faces and well-defined edges. Used on feature walls or where the wall is normally viewed at close quarters and craftsmanship is highly visible.

Medium Stack

Medium stack is defined as stones fitted with joints of 11mm to 20mm. The choice for natural faced, larger, and deeper stones. Racking out gives a negative detail and visual dominance to the stone. Equally various styles of pointing can be applied which adds visual dominance to the lines and patterns in the jointing.

Wide Stack

Wide stack is defined as stones fitted with joints of 21mm to +40mm and deliberated irregular jointing such as with crazy paving where the stones are largely left in their natural state and not trimmed to fit each other. This style was traditionally used where the stones were to be plastered (cement), daub (mud) or coated with harling (lime).

Digger Stack

Digger stack is the use of large rocks too heavy to manhandle into position and seen as a cheap option for landscape retention walls. Amateur built walls are often unstable and dangerous. A stable wall needs the knowledge of stonemason to ensure the stones are shaped to make good flat contact to adequately bear the weight of the stone above, are adequately pinned, levelled, founded and backfilled. It is a two-person job, not a digger operator by himself job. Armouring of stream beds is also essential preparation work.

Bagging

Bagging is a construction and pointing style that references the early field stone and mud buildings of Central Otago. Defining features are stones with natural faces and poor edge definition. Correspondingly wide joints where the mortar often exceeds the area of seen stone so is the dominate visual element. Heavily bagged pointing results from trying the surface flat. It was essentially the first layer of rendering over the stone. The low rainfall in Central Otago meant that limewashing over the mud was durable enough.

Pointing

Pointing is the top finished surface layer of the mortar in between the stones. It is often coloured and harder the mortar. New buildings are normally pointed with cement-based mixes. Historic buildings, reproductions, and restorations are normally pointed with lime-based products of the period.

There are many styles of pointing and they can be main aesthetic of the wall.