The situation at The Anchorage was less dire, with only minor leaks discovered, and Naylor Love, the construction company doing the work on both it and Salisbury Crown, said The Anchorage job was "more of an upgrade".
Said Mr Leishman: "They're a little bit lucky."
Work on re-cladding The Cascades began in November after the roof was largely replaced 18 months ago.
"Like a number of buildings at the Mount, it was poorly constructed and it suffered from water ingress," Mr Leishman said.
Asked to explain the term, he said: "It leaked. Yes, there was water damage in apartments."
Residents have moved out of the building but a business on the ground floor is able to operate.
"[The building] had to be fixed," said Mr Leishman. "There wasn't a way for it to be avoided."
Work to fix the Salisbury Crown began in February after it was discovered to have "water ingress problems throughout the building".
Design problems had also been discovered when the cladding was removed, and repairs included replacing the roof.
Residents have also vacated the Salisbury Crown because, Mr Leishman said, it was not safe for them to stay.
He said the bill for each job is more than $2 million, while the work on the much larger Anchorage is costing almost $10 million.
The work at The Anchorage includes replacing all facades and the roof, but Naylor Love project manager Nigel Lanbourne said although the building had "leaky elements", the job was "more of an upgrade".
He said both it and the Salisbury Crown would be "fully up-specced 2015 buildings in line with the latest building regulations" by the time the jobs were completed.
The Cascades was built in 2000, the Salisbury Crown in 2001 and the Anchorage in 2002.
Mr Leishman, who has specialised in construction problems - in particular leaky buildings - since establishing his company 10 years ago, said the extent of the problem at the Mount was large.
"Probably most buildings built in that era in the Mount will have problems. It's not only apartment blocks, but individual houses.
"There's a bit of a timebomb at the Mount. It's been allowed to tick."
In other territorial authorities, he explained, councils had certified buildings that were leaky, meaning they had a legal obligation to help fix them.
But in Tauranga, during the period when many leaky buildings were built, private certifiers were given the job of signing off constructions and those certifiers subsequently went into liquidation.
"That left the owners with no-one to sue."
As a result, the city was only really beginning to deal with its problems with leaky buildings, and the current jobs had all benefitted from the Government's Financial Assistance Package [FAP] scheme, which is a 25 per cent grant towards repair costs.
He said there was also "a level of denial" among property owners in the Bay similar to what there had been in Auckland several years ago.
But the consequence of not addressing weathertight issues was that homes became uninhabitable. "Doing nothing doesn't solve the problem ... It's never going to get cheaper to fix things. Delay just adds cost."
He said in one case his firm had dealt with, a delay of just over a year had seen the cost rise 14 per cent.
In Auckland, the increase in property values meant owners of leaky properties had been able to absorb the cost to some degree and, although there was a stigma around publicising leaky buildings, people were far better off buying something they knew had been repaired and brought up to current building regulations.
Tauranga City Council said it helped property owners by offering free pre-development information for all forms of building and planning involving weathertightness issues, including advice on the Building Code.
Council spokeswoman Aimee Driscoll said the City Plan provides flexibility to some weathertightness remediation works.
"Tauranga City, like many other cities in New Zealand, continues to work through claims on a case-by-case basis, regardless of whether there was a private certifier involved."
