Pennsylvania bluestone is the most prominent paving material in formal outdoor living spaces throughout the northeast regions. Some people may refer to it as flagstone or slate, but the proper name is bluestone and the majority of it is from Pennsylvania. The natural stone paving material can be found in estate gardens from northern Virginia to Boston. Here in the Lehigh Valley of Pennsylvania, bluestone patios are common around the majestic old homes of West End Allentown, Saucon Valley Bethlehem and College Hill in Easton.
In formal landscape designs, the natural stone is cut in rectilinear patterns for patios. The limit of the pattern design is tied to the creativity of the landscape design and the landscape designer. Random patterns are the most common, but a good landscape designer can come up with multiple paving pattern options to uniquely fir the design. One approach is to install a band of stone on the perimeter of the patio, a running bond pattern in the field and a diamond pattern as medallion in the center.
Pennsylvania bluestone is sorted into various colors, grades and sizes. When left natural cut, the top has a finish known as ‘cleft’, meaning that it has ridges and variations. This rougher finish can be refined by flaming the tops which causes the stone to regularize and leaves a more even textured finish. This finish is most common on the uniformly color range called ‘Blue Blue’ or ‘Thermal Blue’. Classic and formal landscape and patio designs tend to call for the uniform color. Pennsylvania bluestone also comes in ‘Lilac’ ‘Green’ ‘Brown’ and a full color range mix.
Bluestone patios can be installed several ways. The stone can be installed on a concrete slab with mortar pointing in the 3/8” joints between stones. Bluestone can also be ‘dry set’ on compacted stone base much like a concrete paver patio is installed. In that approach, polymeric sand or screenings are swept into the stone joints. A good installer will cut each piece of stone such that they all fit into the pattern with less than 1/8” joints, but 3/8” or more is the common joint for ‘dry set’ bluestone installers. A hybrid method involves installing a bluestone curb and then setting the stone on a damp masons mix mortar bed with each stone custom cut to make the tightest joint possible. This technique is expensive and reserved for only the best masons and the higher budget projects.