Travertine Introduction Part 2 – Extraction and Processing
Extraction of Travertine:
Travertine is generally found on or very close to ground surface, therefore it is commonly extracted by excavating open-pits.
After locating the proper source and performing environmental impact studies, and obtaining official permissions, first the top soil is removed. The stone layers are examined by methods such as obtaining rock samples, core drills or visual observation, Ground Penetration Radar GPR. Since travertine is usually deposited in horizontal bands, it makes sense to extract in slabs.
Then the cutting operations start. The goal here is to extract as large blocks as possible with as minimum damage as possible. Cutting is usually done by wire saws, chain saws or splitting the stone with edges using hydraulic jacks. Both the wire or the chain saws contain diamond particles, the hardest of stones, in order to easily cut through travertine which is relatively far softer. Wire cutting is more precise that produces very neat cuts with little vibrations and more suitable for harder travertines. Chain cutting is better for obtaining large blocks with deeper cuts, in relatively softer deposits.
Wedge splitting is a cost effective method, after the initial cuts are made and the boundaries are determined.
Less commonly, explosives may also be used. This is done in a controlled manner to economically loosed large parts of rock, however it is not a precise method and there is the risk of producing excessive amounts of undesired fractures, which increases waste. It is also the least environmentally friendly method.
After the blocks are cut, the are lifted from place and then transported to nearest processing facility for processing. Each block usually weights at least several tons and can be upto a few meters in size.
Processing of Travertine:
The blocks are processed to make them suitable for final use.
First the blocks are sliced into thinner pieces as slabs, tiles, or other shapes as desired by saws such as wire or gang saws. Cutting can be as vein cut or cross cut, which indicates the direction of cut with respect to strata in the stone. Cross cut means the cut is parallel to strata and vein cut means perpendicular with respect to strata. One versus the other method of cutting means very different end products, even if they all come from the same block initially. The traditional way of cutting is the vein cut, which means the strata on the stone that formed in millions of years, will be visible on the finished stone face during its use. Cross cut, which is relatively newer technique does not show the strata, instead, lighter and darker shades of the stone will be visible all over the surface. Cutting can also be performed by CNC machines, which allow more complex shapes obtained precisely and repeatedly.
After cutting operations are finished, the surfaces may be polished, honed, brushed, chiseled or left untouched, depending on final intended product type and its use.
As we mentioned in Part 1, travertine has pores and cavities. these may be filled with cements or resins to increase strength and improve appearance.
Therefore all these cutting and finishing operations also play crucial role in final product’s appearance.
The final product must be free of cracks and be of sufficiently consistent color.
