He is re-fitting the older 17-level office tower on Princes Street off Shortland Street at The International where Donald Trump advisor Chris Liddell was reported to have bought the $15.2m penthouse, although Groves has said he cannot comment due to confidentiality arrangements.
A Sanctuary spokeswoman said exterior cladding had been removed from the existing building via a 40m tower crane.
Groves said deposits had been taken on 55 apartments, sold for $1m to $15.2m.
"The housing market hasn't made any difference to our product. It's been steady sales. Owner-occupier product seems to be less affected by lending loan to value ratio restrictions and also we sold to any offshore buyers," Groves said.
The block behind the Grand Hotel's facade was developed by a Fletcher business with Argus Questar between 1988 and 1990 and incorporated the hotel's facade in a period when old buildings were demolished, with only their faces remaining.
Jasmax designed Sanctuary's changes, working with interior designer Rufus Knight. One, two and three-bedroom apartments are to have Italian-designed kitchens, German appliances and natural stone features.
The spokeswoman said interior fixtures, fittings and walls had been removed. A new glazing system would be applied soon.
"We've got petitioning in on two levels," Groves said.
The project is due to be completed in the middle of 2019.