At Cumbrian Stone we believe that it is important to understand the process of manufacturing natural stone components in order to appreciate the versatility and natural beauty of sandstone as a raw material. The production of natural stone units for any project must go through a number of stages before a project is complete; these processes can vary depending on the nature of each project and the type of stone being cut, and an overview of this process is a s follows:
Quarrying Sandstone Blocks
The quarrying process involves the extraction of unprocessed sandstone blocks from the quarry. This is normally achieved through the use of one of three different methods:
Feather and Wedge – This is a traditional method of extracting stone blocks without the use of explosives. The top of the stone bed is exposed and holes are periodically drilled down into the stone face. A steel wedge is then inserted into each hole in between two thin steel strips known as feathers. Each wedge is then struck simultaneously with a hammer in order to create cracks along the line of the wedges. Finally bars are inserted into the cracks in order to lever the blocks out from the quarry face.
Channelling – This process involves the mechanical cutting of a long, thin strip into the top bed of the quarry; this strip can be up to 3 metres deep depending on the size of block required. Horizontal holes are then drilled into the front face of the in order to meet the channel at its base, before the individual blocks are then prised free of the quarry face.
Blasting – This is the most common method used when quarrying natural stone as it is the most cost effective and economical for removing large quantities of stone for processing. Holes are drilled into top bed of the quarry face before being partially filled with a calculated amount of explosive. The quantity of explosive used is enough to create fractures in the stone without shattering the block. Once these explosive charges have been detonated the loose block can then be pulled away from the quarry face.
The first stage of manufacture is always Primary Sawing. This process involves the cutting of the quarried sandstone blocks into slabs. This is also known as “sawn two sides” as only two faces of the stone are cut at this stage.
The cut slabs are then checked for suitability before being allocated to different projects based on the quality of the exposed stone. Stone slabs containing a large number of flaws or cracks are allocated to walling production, while higher quality slabs are allocated to bespoke masonry components.
Any flaws within the stone are also marked on each slab so that these can be avoided during secondary sawing.
The next process for bespoke masonry units is Secondary Sawing. This is carried out using one of the smaller saws, where the stone slabs are cut to the finished sizes shown on the cutting schedule.
This is known as “sawn 6 sides” as all six faces of the stone are sawn at this stage.
Once these blocks have been cut they are again checked for any newly exposed faults before being passed on to the next stage of production.
Profile Sawing and CNC Machining
Once the stone blocks have been cut to the finished size (sawn 6 sides), they are ready to carve into the finished profile of the stone. There are three options available to carry out this work, and the most suitable of these is determined by the detail and finished profile of the stone.
The first of these options is to profile the stone using a profile saw. These saws will cut a straight linear run of most profiles into the face of the stone, making this method ideal for string and cornice courses. This is also the fastest and often the cheapest method of finishing detailed stone units.
The second option available is to finish the stones using a CNC 5-Axis Saw. These saws are fully automated, and cut to a pre-set programme using a variety of blades and tools. This allows for cutting more intricate details and for working on more than one face of the stone at a time.
In order to generate a programme for the CNC Saws a 3D model of the finished stone needs to be created using CAD or similar software. Toolpaths are then added in by the programmer in order to instruct the saw on how to carry out the carving work. This process is ideal for detailed units where there is a lot of repetition or multiple identical units that are too complex for cutting using a Profile Saw.
Masonry and Hand Carving
The third and final option available is to finish the stones using traditional hand carving techniques. This method allows for full flexibility in how the stone is dressed, with the masons utilising a selection of tools ranging from small cutting discs to tungsten tipped chisels depending on the finish they are looking to achieve.
The use of power tools in hand carving has made some elements of hand carving faster than it would normally have been, however generally the techniques and skills used by our masons are the same as those that would have been used historically.
It surprises a lot of people to know that all of our walling is hand dressed in order to ensure the best possible quality. This method ensures accurate course heights, square arises and a natural, pitched face to each and every stone we produce.
The walling process starts with long slabs at set heights being split using a guillotine. Each stone is normally split to give a 100mm bed depth, and as standard we produce our pitched walling at heights of 65mm, 140mm and 215mm as this ensures correct coursing with 10mm joints.
The face of each stone is then hand pitched before being palleted and shrink wrapped for distribution.