The stone cutters

Under new owners the Hinuera quarry in the Waikato has a new lease of life.   By ALAN TITCHALL.

Since 1954 the Hinuera quarry near Matamata has been under the Firth Industries umbrella of businesses, producing stone product that has become popular in the building industry for use as aesthetic and durable cladding and paving.

Hinuera is one of a few quarries in New Zealand producing large quantities of unique natural stone, the other major producer being Parkside (Oamaru Stone) in the South Island.

In April 2007, Firth sold out to a small group of private investors and the business now operates as Hinuera Natural Stone.

The quarry retained its original 25 staff and has undergone an extensive refurbishment over the past year, increasing production to satisfy a strong demand in the high-end housing and paving markets. A diverse range of stone building materials are produced, from sawn and splitface veneers, to fireplaces, pool copings and decorative stonework.

The cliff-face quarry is located in the Hinuera Valley on State Highway 29 at Piarere, overlooking some of the country’s most attractive and expensive farmland. Although widely thought of as sandstone, the resource is a deposit of ignimbrite (volcanic stone) that came from a central volcanic plateau eruption at Mangakino about 1.3 million years ago. Its colour varies from cream to reddish brown after it has been kiln-fired. 

This quarry was bought with the knowledge that investment was needed to bring the operation back into full swing. Cutting produces a high volume of waste and in previous years a decision was made to quarry south of the reserve and the overburden spilled over on the floor and up over benches of the old northern face. When the southern end of the deposit ran out of good stone, only the very upper reaches of the northern quarry with its lower quality rock were accessible.

“We have removed 90,000 cubic metres of overburden already, and recontoured and hydro seeded the batters in the quarry,” says manager Harry Toa.

“And thanks to the co operation of our neighbours, we have managed to achieve this in a very short space of time.”

Under consent, most of this waste has been dumped onto a leased paddock next to the quarry entrance where it has been used to fill up hollows and re-grassed. Restoration work in the quarry will continue for some time, he says.

Harry Toa is ex Winstones and has a long-standing reputation in the industry as a ‘fix-it’, hands-on manager. He has been involved before in cleaning up and putting new life into tired quarries, and has been very effective in overseeing the extensive stripping and cleaning programme at Hinuera. His career has taken him far and wide, from Taupo to America Samoa and Bolivia, where he was working for Fletchers. His hands-on approach was evident when Q&M paid a visit to the quarry and found him driving a large payloader over the fill site.  He took a spell to show me around the quarry with its neatly ‘sculptured’ faces made up of 10 benches, each around two metres high and made up of different grade stone with the quality improving with depth.

“The top five levels are coarse grained, vitric grade stone that is interspersed with pieces of pumice that give it a speckled character when cut. Its natural cream or buff colour changes to terracotta or golden brown when kiln fired,” he says.

“The middle layers are more solid duro rock, and the last three benches contain the top quality and very solid statutory rock, which is smoother with an occasional grain and water markings, similar to wood grain. It has a natural fawn or cream colour.”

Each bench is quarried to order and processed on site. As a low volume quarry, Hinuera has estimated reserves of up to 400 years, says Toa.

A hand-picked team of five is currently employed in the quarry to extract the stone. After the thin level subsoil is removed, the stone is cut vertically with Italian designed, hydraulically driven, Pellergini saws with a cutting depth of 2.5 metres. After lined up on tracks the blade of the saw is swung down into the rock and, very slowly, a channel about five centimetres wide is cut through to the face and then cross cut. Horizontal cuts are made using a wire saw or the bottom is ‘fractured’ off along it natural faults. Slica shards and pumice in the stone, that give it such good acid resistance and durability, are very abrasive on the cutting gear.

The free-standing blocks and even entire walls are prised apart and snapped at their fracture points using airbags in the cuts.

“It is important that we study and work out the natural fracture points of the stone early in the process,” says Toa. “It’s too late once it goes into the factory. You don’t want pieces breaking off during the final cutting.”

Other than management and manpower, the other essential investment in getting Hinuera back in good working order was in new and upgraded machinery, including a 42 metre Favcotower crane. The 12 tonne capacity crane with its luffing boom was commandeered from a subsidiary company building site in Auckland and has proved invaluable for handling the big slabs of rock and lifting gear onto different benches ascending the quarry face.

This lifting crane is a huge improvement on the derrick cranes used in the past, says Toa.

“With the extra reach of the new crane, the quarry now has the potential to extract up to 36,000 square metres of processed stone per annum.”

Once cut from the face, the 2x2x1 metre billets (weighing between five and eight tonnes) are transported on a front-end, 380 Komatsu loader to the cutting shed and masonry factory. Here they are cut down for cladding, paving, split stone veneer, or bricks.

 The billets are first cut into manageable sizes with a primary 2.7 metre diameter rotary saw featuring cutting tips made of tungsten carbide impregnated with industrial diamonds. An ear-muffed breakdown crew separates the cut billets from the block and prepares them for finishing on any of three smaller, semi-automated saws, or process them into splitstone veneer.

A specialist area in the masonry factory is dedicated to making fine stoneware articles such as fire surrounds, columns, headstones, benches, seats and windowsills. Not exactly a career path in New Zealand in past decades, two stonemasons had to be recruited from the UK for this fine work. The investment is paying off. Export has been confined to the Tasman in the past, now enquiries and even orders are coming in from the likes of the UK and South Africa.

Hinuera’s own administration offices demonstrate the versatility of the stone – natural or kiln-fired, smooth or rough surfaced. However, Harry Toa is the first to concede that the administration site and parking areas should be next in line for a refurbishment. He also points out over the leased farmland to the side of the long, and attractive, entrance road.

“We’ll open this area up with maybe a visitor centre and other public facilities that show off our products.”

Somehow, I doubt if Harry Toa will be around to see it. He would have been moved on to the next quarry crying out for help.