The roof slate industry began to bounce back in the 1980s. Much like before, the process of manufacturing roof slate begins at the quarry where slate is extracted from an open mine called a “pit”. Access roads allow for safer mining operations (gone are the days of workers having to climb in and out of the pit on rickety, makeshift ladders). Waste rock or “rubbish” is seen on the right of the photo. Turning slate into usable products such as roof slates, floor tile, countertops, and flagstone has a 90-percent waste factor. Photos by Tim Healey with permission from Camara Slate Products
A John Henry excavator mounted rock drill, seen here in the center of the pit, is used to core 30-foot-deep holes into the slate deposit for the placement of explosives. After blasting, the resulting large pieces of slate or “blocks” are transported by a big-haul truck from the pit to a nearby processing mill. Pooling water, seen here on the right, needs to be pumped out of the pit daily.
The access road to the quarry, looking north (left). Slate deposits in the region lay at an angle in the ground—roughly 30- to 45-degrees. Quarriers in the past predominantly worked the highest quality slate deposits (the higher-quality slate back then could be split as thin as 3/16 of an inch as opposed to today’s minimum thickness of 1/4 to 3/8-inch). Modern tools allow today’s slate companies to manufacture slate products from lesser quality deposits. That said, the slate from this quarry passes the S1 standard (ASTM C406) and has a 75- to 100-year product lifespan.
At the mill, workers first use an air hammer to split a slate block down to 6-inch-or-less thicknesses in order to fit under the arbors of the cutting saws. Upon excavation, slate has to be managed carefully. It has a certain amount of moisture content and its cleaving planes can be ruined if the stone freezes or it lays out in the sun too long and dries out; wind is also a factor in freezing and drying. Each fall, slate blocks are stacked in the storage building beyond to help maintain production in winter.
The split blocks are first loaded onto a conveyor leading to the cutting rooms. A gauging bar spanning over the conveyor keeps oversized blocks from entering the cutting room.
The block is cut to the desired width and lengths using wet saws equipped diamond blades.
The cut pieces are conveyed from the cutting room to an adjacent splitting area.
Much like quarrymen from the past, a worker hand splits slate with a hammer and chisel (left). Here, he starts by splitting a cut piece of unfading gray slate starting at an inner third point (right). He’ll then split the cleaved-off third piece into the desired roof slate thicknesses.
A worker splits a cut piece of purple slate (left, right). Splitting is just one of many quality-control points along the production line. Uneven cleaving planes and hidden imperfections, such small seams of flint, render many a cut piece of slate useless.
The split slate is sent from the cutting mill to the finish mill on pallets ready for trimming. They arrive in “chip form” (sawn on four sides to a certain length and width) on either “breakdown” pallets or “book form” pallets. Here, breakdown pallets holding various sizes of purple slate is seen in the foreground, while book form pallets of uniformly cut unfading mottled green and purple slate are in the background.
The trimmer cuts the slate down to its finished size (left), putting a chamfered edge on all four sides of the slate; the chamfered edge creates a shadow line when roof slate is installed. The trimmer blade comes in two sizes (right), the smaller blade is used to trim thinner slate, the larger for thicker material. The blade consists of carbide bits soldered onto a steel blade.
Fastener holes in the slate are made with a hole puncher. The motorized hole puncher (not in use) has a cam which oscillates the punching bits (left), while an old-style punch uses a spring-loaded arm to make a striking motion (right). The slate is punched from the back, which creates a blow-out hole in the front that nail heads countersink into (nails are used to “hang” roofing slate rather than fasten them down).
The holing process for thicker material, such this 3/4-inch-to-1-inch-thick piece, is done with a hammer-drill with a long masonry bit.
The front of a 1-inch-thick unfading mottled green and purple slate after hammer-drilling the punch holes. Pricing for a square roof slate ranges widely due to color selection and thickness. The least expensive slate is roughly $400 a square, while the most expensive goes for over $2,000 a square.
Forklifts are used to ferry pallets of finished and “chip form” slate ready for trimming around the slate yard.
Slate is typically transported by semi-trailer trucks. The load shown here is destined for Dallas, Texas.
Shawn Camara of Camara Slate Products, Inc. (left, foreground) shows attendees of “Slater Day” at the Slate Valley Museum how to hand split slate. Photo by Tim Healey