Splitting Methods

Blasting

To blast a stone apart first a large diameter (2 inches) round hole was drilled in the stone to a depth of one to two feet deep. Then the hole was filled with gunpowder and ignited. The force from the blast split the boulder into irregular pieces.

A typical 2 foot deep round blast hole (Newbury, MA)

Triangular Hole

As the name implies this hole has three sides. Triangular holes were used primarily for blasting. The points of the hole helped to direct the force of the blast and therefore offered control over the direction of the fractures in the rock.

Plug & Feather - Farmer’s Version (circa 1774-1810)

An early version of the plug & feather method. The method was an improvement over the blasting method as it often times produced pieces of stone with a flat face suitable for building with.  Unlike later versions, the early plug & feather method  used  a maximum of 3 holes. A person drilled one, two or three round holes per boulder as he saw fit. These were generally small holes about one inch diameter and from two to four inches deep. Two half-round shims were placed in each hole and a metal wedge was placed between them. The shims were used to keep the wedge from hitting the bottom of the hole. When a wedge hit’s the bottom of a hole it often times flies out of the hole and becomes a very dangerous flying projectile.  Once each hole was filled the shims and wedges, a person with a small hammer about three pounds in weight, hit each wedge until he heard a cracking sound. At that point he let the boulder finish splitting apart on it own.

Field boulder split using an early plug & feather method. The foundation is circa 1790-1825.
(South Hampton, NH)

Plug & Feather Method - Commercial Version (1803-Present)

In this method small round holes were drilled every six to seven inches across the whole stone. This proved to be a major improvement over the earlier version that used 1 to 3 holes.  By placing holes every few inches along the intended split a person was able to get regular blocks of stone. A regular block had all straight sides. Over time the half-round shim developed into a small half-round shim with a feathered or thinned out top that curled over. Hole sizes shrank a little to ¾ inches in diameter and down to two to three inches deep. The method of drilling and splitting was the same as the earlier method. Stone bars and blocks from approximately 1803 onward used this method which is so common throughout New England.

Plug & Feather Method - Commercial Version
Source: Rock Excavation: Methods and Cost, By Halbert P. Gillette (New York: M. C. Clark, 1904)

The modern version of the plug & feather method features uniform round drill holes placed every 6 to 7 inches.

Flat Wedge Hole (Invented in Quincy, Massachusetts in 1803)

Flat wedge holes are as common as round holes. They are often times found in the same wall together and sometimes on the same piece of stone. The flat wedge hole method utilized a different type of cutting tool which was not exactly a drill.  The tool was a cape chisel. It chipped the hole out rather than drilling it out. A cut away view on a split piece of stone shows a trapezoid shaped hole. A hole that is wider at the top than at the bottom. This hole is narrow usually a half inch wide when whole. The size varies but is around 2 ½ inches at the top, 1 ¾ inches on the bottom and approximately 2 inches deep. Holes were placed every four inches across the line of intended split. Flat wedge holes also had feathers but theirs were much thinner and a wedge. To split the stone apart the wedges were tapped in sequence along the row of holes. When a crack was heard, the quarrier waited for the stone to finish splitting on its own.

This method was phased out by the 1870’s and was forgotten.

Source: The information on stone splitting and quarrying comes from the book The Art of Splitting Stone. The book discusses the various methods, tools, and types of quarries in greater depth. In additional, it quotes source documents and discusses archaeological sites important to the study of early New England quarrying. It is excellent resource on the subject.