Dora Yeoh runs her hand across a large granite desk in one of the six towers that make up the Toronto-Dominion Centre in the heart of Toronto's financial district.

As senior manager of tenant projects for Cadillac Fairview, Yeoh is overseeing a $250 million revitalization of the iconic cluster of skyscrapers 50 years after the first building in the business complex was constructed, dominating and transforming the city's skyline.

"It is all about the details," Yeoh, an architect, said Tuesday of the revitalization, which has been underway since 2009.

The first tower in the TD Centre business complex, which officially opened 50 years ago, was Toronto's first modern skyscraper. 0:26

In each of the six towers, five of which are painted black, exteriors are being repainted, roofs are being replaced, double glazed windows are replacing single glazed windows from the second floors up, mosaic ceiling tiles are being salvaged, scrubbed and reassembled, and the interiors of lobbies are being renewed with ground floors being restored.

That means, among other things, existing desks are acquiring new storage cabinets and new umbrella trays. In at least one building, a major leak has been fixed and new LED lights have been installed.

The TD Centre is celebrating its 50th anniversary this month, an event that coincides with Canada's 150th birthday.

Dora Yeoh, senior manager of tenant projects for Cadillac Fairview, says: 'It is all about the details.' (David Donnelly/CBC) On July 1, 1967, the first tower in the complex was completed, making it Toronto's first modern skyscraper. Ludwig Mies van der Rohe, a renowned German-American architect, designed the complex. Its low-rise banking pavilion and five additional towers were built from 1969 to 1995.

Now, an estimated 21,000 people work in the complex, which is owned by Cadillac Fairview and the Ontario Pension Board. It includes a public plaza, with seven courtyard cow sculptures by Joe Fafard. The banking pavilion has a living green roof. One of the six towers is pink granite. The complex has more than 70 tenants.

"Every tower is in a different phase of revitalization," Yeoh said.

"As a building owner, you have to maintain the assets so that they are still attractive for people to lease. From an environmental perspective, the greenest building is the one you don't have to rebuild," she said.

"To update the buildings in this way speaks to the original design and to the responsibility that Cadillac Fairview feels for the assets. For the city, it is literally the heart of the financial district."

As Yeoh gives an impromptu tour of the complex, located near King and Bay Streets, workers on scaffolding are painting the exterior of the main building, the TD Bank Tower at 66 Wellington St. W.

Now that the weather has taken its toll, the exteriors look nearly battleship grey, Yeoh notes. The TD North Tower, at 77 King St. W., took four years to paint. Grey primer is used to ensure painters can see which spots they have missed. Yeoh says PPG fluoropolymer paint, an industrial strength variety, is being used.

The TD Bank Tower and the TD North Tower, pictured in the early 1970s. World renowned architect Mies van der Rohe's design transformed and modernized Toronto's skyline, bringing it into the modern age. (Cadillac Fairview) "It's a fabulous finish," Yeoh says of the paint.

David Hoffman, general manager of the TD Centre, said the revitalization project is a large capital reinvestment in the property and it is significant to Toronto because the buildings have symbolized business leadership in Canada and the power of real estate to drive innovation for 50 years.

"At the time when it was built, the property did really set a new standard for architecture and design," he said.

"This is multi-year, multi-tower program. The goal is to maintain these buildings to their best-in-class position. The scope of the work has included the building envelope, mechanical and electrical infrastructure systems, elevator and escalator modernization and upgrades, interior work which includes the main lobby and washrooms, and exterior plaza rehabiliation work."

Hoffman said the property helped to develop the city's financial district. "It introduced the modern workplace to Canada," he said.

The first tower in the TD Centre business complex, which officially opened 50 years ago, was Toronto's first modern skyscraper. (David Donnelly/CBC) "Revitalizing builds on that legacy. We are always trying to reach to new heights."

Yeoh said much care has gone into individual aspects of the revitalization project.

"We have to maintain the original design intent but we also have to understand that our tenants have to maintain their businesses," she said.

"There's not that many materials here. You have travertine, you have granite, you have the steel. The whole thing about Mies is that he likes to bring the inside outside. So you will see that the grout lines of the wall go to the floor. The whole complex is based on a five-foot by five-foot grid."

For example, in the TD North Tower, the first building to be revitalized, the ceiling has glass mosaic tiles that needed redoing. "I personally spent months going to all these different glass tile companies to say, 'Hi, can you match this?'"

Yeoh went back to the original company that manufactured the tiles, which no longer had the original formulation. It offered to do a custom job, but a deal could not be reached, she said.

David Hoffman, general manager of the TD Centre, says: 'At the time when it was built, the property did really set a new standard for architecture and design.' (David Donnelly/CBC) "What we did is we cut the ceiling down, in three foot by three foot pieces with the drywall, so the mosaic tile was still attached to the drywall. They put it on pallets and then shipped it up to York Marble. So York Marble would take these pieces of ceilings, they would soak it for 24 hours and they would scrape the tile off. Then they would put it in a tumbler to clean it off, and there would be literally be guys with toothbrushes."

The tiles were salvaged, one new tile was mixed in to make up for tiles that were lost, then the tiles were put back onto plastic sheets and reassembled. "It was exactly the same as you could get at Home Depot, just much more expensive," she said.

Yeoh declined to say when the revitalization will be complete.

Work on the TD Bank Tower, which includes exterior painting and window reglazing, began in 2012 and will be finished at the end of 2018. About 85 per cent of work on that tower is finished. Work on the TD North Tower was completed in 2009. Its ground floor has been restored, its exterior repainted and its windows reglazed from the second floor up.

The ground floor of the tower at 222 Bay St. was restored in 2012. Restoration of the ground floor at the TD West Tower, 100 Wellington St. W., began in 2016 and will be completed this year. In 2014, the roof was replaced in the TD South Tower, 79 Wellington W. And in the plaza, where the cow sculptures sit, all existing pavers have been replaced and waterproofed.

"It's such a long process," she said. "We have a 10 year capital plan."

Hoffman said the majority of the work is expected to be done within four years.

The TD Centre is celebrating its 50th anniversary this month, an event that coincides with Canada's 150th birthday. (David Donnelly/CBC) The TD Centre has a commemorative exhibition in the foyer of its main building to mark its anniversary. The exhibition will run until the end of August.