He and wife Susi, of Dunedin, bought the former Lawrence Town Hall five years ago and converted it into a retro Art Deco collectables shop, Daphne and Apollo. Mr Nicholson said his father, also Warwick, taught him a great deal about lime and mortar, repointing and working on old buildings.
He said the Town Hall was built in 1875 during the gold rush days. It used to be two storeys and was one of the finest stone buildings in Lawrence.
''I've been told it was the largest and most expensive building of its type in Otago,'' Mr Nicholson said.
He said it was designed by Robert Arthur Lawson, who also designed the First Church in Dunedin.
''Lawrence was a rich town back then - bigger than Dunedin.
''They finished the building, the gold ran out and the money ran out and it had 60 years of basic neglect.''
Mr Nicholson said the sturdy building had been well made from local rock, with the interior grain running in three different directions.
The exterior wall had horizontal reinforcing every 45cm and the internal brickwork was reinforced as well.
Many similar buildings in the town had been demolished.
''We liked the building and wanted to save it,'' he said.
While the building is still sturdy, the exterior walls needed repointing and cement used as a ''patch up job'' had to be removed.
He removed the corrugated iron used to patch up the front facade and found the original arches.
''The locals thought I had put them in, but they were there all the time - they just hadn't seen them for so long.''
He dug out the old mortar, then replaced it with the same mortar but added additional lime to the mix.
Lime mortar has to be softer than the material it surrounds, and as it is less dense, it does not trap water in the walls, unlike modern cement.
He chose not to use modern cement because, when there was a frost, it ''blew the bricks out''.
''The purpose of lime and mortar is not to glue the stones together (like modern cement) but keep them apart and fill in the gaps between the stones.''
Mr Nicholson has spent three weekends working on the one wall and only has a little bit more to do before he starts work on the interior. He estimates he saved himself about $10,000 by doing the work himself, although he has had help from others.
''You are never going to get it the way it was - just enjoy it the way it is,'' he said.
by Yvonne O'Hara