Dry-Stack Stone Walls:
Stone masonry originated with dry-stacked stonework where the walls are carefully layed up without mortar. Gravity serves as the glue that holds everything together. Free-standing dry-stack stone walls are usually made larger at the base and then taper in slowly as the height increases. For absolutely no expense but the labor, farmers built miles upon miles of stone fences this way in Ireland and in the northeastern states.
Many old Irish houses were built in a similar way. Where “mortar” was used, it was often merely mud or limestone plasters with little strength. The mortar functioned as caulking to stop the flow of air, rather than as cement to bond the stones together. Short, dry-stacked stone walls are especially ideal for landscaping projects. Taller walls require more skill and time. For more details on dry-stack stone walls, be sure to check out Building Stone Walls and Stonework:
Techniques and Projects.
Mortared Stone Walls:
Mortared stone walls evolved out of dry-stack stone work with the emergence of cement mortars. The first cements were made of burnt gypsum or lime mixed with water to make a paste with slight bonding capability. Stone walls still had to be built as carefully as they were without mortar. The cement paste just filled the gaps between the stones and cured to form a soft, rock-like substance.
The basic formula for modern cement originated in England in 1824. It is called “Portland cement” because the color is similar to the rocks on the English island of Portland. It is still called Portland cement everywhere in the world it is manufactured. This cement is made with calcium from limestone or chalk, plus alumina and silica from clay and shale. The ingredients are ground, mixed in the right porportions and burnt in a kiln at a temperature of about 2500 degrees F (1350ªC) to drive out water bound up in the raw materials. In the kiln it fuses into chunks called clinker. It is cooled and powdered, and gypsum is added to control how fast it sets up. Portland cement is mixed with sand and water, and often lime to make a smooth mortar for stone and brick work. Adding the lime makes the mortar softer and more flexible.
With the aid of Portland cement it is possible to build a taller stone wall that does not taper inward like a dry-stacked wall. The cement has some ability to “glue” a stone wall together with less care, but proper stoneworking techiques are still important. Building a free-standing stone