Forrester Gallery’s Facelift: Lime Mortar and Lime Plaster

Published on 01 May 2019

By Heather Bauchop, Heritage Advisor 

Over 130 years after contractors Philpot and Matheson erected their scaffolding and ascended their ladders to work on the Bank of New South Wales, Waitaki District Council Projects and Assets Officer Grant Rhodes is overseeing repairs to the Oamaru stone building. Rhodes is working closely with Heritage New Zealand’s buildings conservator (a stonemason by trade) Andrew Barsby, and conservation architect Robin Miller. 

Andrew Barsby tells me there is no cement being used in the works, instead a natural hydraulic lime imported from France is used in the mortar and plaster mixes. The lime mixes need a bit more care than cement – pre-wetting the stone before applying the mix, and keeping the mix damp for as long as is practical after it has been applied. Cement, Andrew says, is too hard, too impermeable and too brittle to use with the softer limestone. 

Dooley’s Stonemasons are carrying out the work with lime mortar and lime plaster – returning to the technologies used in the bank’s original construction. The chance to trial different mixes and to restore the former Bank of New South Wales using traditional materials adds to our knowledge of working with the stone and gives the ‘graceful while massive’ bank an age-appropriate facelift.

Lime putty has been a base ingredient for mortar and plaster into the distant past – it’s even been found in Egypt’s pyramids. Portland cement, on the other hand, has only a hundred-year history. Forrester Gallery, currently clad in scaffolding is having its own history revisited as tradespeople repointing the limestone and repairing the eroded stone of the former Bank of New South Wales.

In 1883, Dunedin-based contractors Philpot and Matheson relocated to Oamaru to construct architect Robert Arthur Lawson’s design. The North Otago Times crowed over the ‘exceedingly handsome building in the full Corinthian order of architecture, the beauty of which will be enhanced, as in the National Bank, by a piazza, having a parapet and balustrade, supported by six projected fluted Corinthian columns.’ 

Bank of New South Wales at its resplendent best (Photograph, Waitaki District Archives)

Contractors for the Bank of New South Wales selling off their building equipment when the contract was complete (North Otago Times, 6 August 1884, p. 3.)