Baumberger sandstone is a fine grained and yellowish grey sandstone and has been mined for centuries near the northern edge of the Baumberge Mountains. It was used extensively in Münster (North Rhine-Westphalia) and the surrounding region for both internal and external applications. Since the calcite content can range between 50% and 70%, it is frequently described as a very sandy limestone or limestone. Fark Naturstein in Havixbeck own one of the few remaining quarries to extract Baumberger sandstone calling on eight generations of experience as stonemasons.

Fark’s quarry covers an area of around 10,000m2 and the Baumberger sandstone deposit consists of a 4m thick layer located under 20m of overburden.  The dense, homogenous, fine grained and relatively soft (compressive strength 40-50 MPa) rock can be divided into three different sections, where the characteristics of the rock determine suitable applications. The softer and malleable rock is suited for internal applications (e.g. fireplaces), the slightly harder and more wear resistant rock is suitable for paving slabs whilst the harder, more weather resistant rock is suitable for cladding.

Cutting rather than drilling and splitting

After the overburden had been removed, stone blocks were broken out using a 45t excavator with a claw attachment. These blocks were then shaped into rectangular blocks suitable for processing by drilling and splitting using wedges and feathers. Shaping the blocks was a time consuming process involving heavy, tedious manual labour which also resulted in a relatively high wastage rate due to unavoidable spalling. Following detailed consultation with Kemroc’s sales manager Enrico Trender, an ES 110 HD universal cutter attachment was supplied to the quarry for initial testing and evaluation. This attachment proved to be well suited for use on the company’s smaller 24t excavator. Having completed a number of successful trials, Fark Naturstein has now started the new season with a completely new process.

The individual steps in the quarrying process consist of cutting a vertical slot in the sandstone deposit using an excavator and cutter wheel attachment. The slot is used by a 45t excavator with bucket to pull large sandstone blocks out horizontally from the main deposit. The large blocks are then cut down into smaller, more manageable sized blocks using the 24t excavator fitted with the Kemroc ES 110 HD universal attachment with cutter wheel (1,000mm cutting depth). All the rough-hewn surfaces on the blocks are also dressed by the cutter wheel so that the blocks have a perfect oblong shape. This saves storage space in the quarry since they are ideal for stacking one upon another. With flat external surfaces, the blocks are also optimally dressed for the next operation at the saws.

Better accuracy, speed, and comfort

Kemroc’s ES range of universal cutter attachments are said by the company to be exceptionally versatile, equally capable of cutting small slots in concrete or asphalt and accurately profiling horizontal and vertical surfaces. They can be fitted either with a cutter wheel or with a cutter drum and once mounted on and powered by the carrier machine, they can be used for work on concrete, asphalt, or rock. After consultation with Enrico Trender, the stone masons at Fark decided to try the largest model ES 110 HD (110kW) fitted with a cutter wheel with maximum cutting depth of 1,000mm as a suitable attachment for their hydraulic excavator.

They agreed on an excavator and attachment combination that used a high torque motor to develop peripheral cutting speeds at around 42 rpm which was ideal for this application. Through trial and error, the operator found that a relatively quick back and forth motion of the cutter wheel in the slot with an advance of about 5cm per cut provided the best cutting performance. In this way there was little risk of jamming the cutter wheel in the slot.  As a result of using the new production method, Fark Naturstein has not only significantly increased the percentage yield of its valuable sandstone material by cutting the blocks instead of using the old drilling and splitting method, but also have saved a lot of time and hard manual labour. “Previously, we needed a good half man-hour of work for a linear metre at a depth of one metre,” calculated master stonemason Thomas Fark. “But now the excavator operator can achieve the same result in just five minutes working with a joystick! For us, this is a completely new level of quality and work comfort.”