Quarrying News...

Saturday, October 11, 2014 at 02:45PM
Studio Practice, Private Commission, Outdoor Sculpture

11th October 2014:
Last week I did something I love, spending time at the top of a hill/mountain, in all weather conditions, working rock. In this case it was the splitting of a thirty tonne boulder of Diorite from Penmaenmawr Quarry, just down the road from Bangor. Unusually for me, this quarry is an aggregate quarry, the land leased from The Crown Estate, by Hanson Aggregates. All of this quarrying material is blasted from the rock face with dynamite, fracturing it into smallish blocks which are then crushed up into smaller pieces used for concrete, Black Top road surface and other aggregates sources. Blasting means that the rock is usually riddled with fractures and therefore no good for making things from, but the particle block I found had about forty feet of rock between it and the dynamite blast, which meant that the major force of the explosion was taken up by other material, simply pushing this boulder into the heart of the quarry.

Upon inspection a month ago, it appeared sound (free from faults) so I went back last week to drill and split the boulder in two, in order to reduce its transport weight up to the Aberdeen saw mill. This was done by using a pneumatic rock drill to place a straight line of 32mm diameter holes across the boulder. I drilled twenty five holes, each to a depth of 900mm, in order to weaken the rock, just like the perforations around a stamp. I then placed plugs and feather, expanding metal wedges, into the holes and took three quarters of an hour hitting them evenly in order to create a sideways pressure which eventually cracked the parent block just where I wanted, in a straight line.

Splitting rock with plugs and feathers is peculiarly exciting, particularly when you actually hear the rock slowy splitting, as if you are tearing it apart. Something that never ceases to maze me is that rock, even extremely hard Diorite, a type of basalt, is actually elastic: you can see the split appearing on the top of the rock, well before it continues down the slides and then, with a load crack, it is parted.

This rock will become the main reception desk for The Crown Estate's new headquarters in Piccadilly.