Experts in paint and plaster are inspecting the ceiling of the historic Assumption Church in Windsor.

Built in 1842, Assumption Church has been closed to parishioners since 2014 because it was deemed unsafe by the Diocese of London.

On Thursday, crews went into the 174-year-old church with a bucket lift to inspect the plaster in the ceiling.

"Even if we were just looking at restoring, for the people that working here we got to know what it takes to make it safe," according to Paul Mullins, a local lawyer who is spearheading the most recent efforts to reopen the church.

Mullins tells CTV Windsor it’s going to take a lot of time and money.

"Theres a heating issue that is a problem, there’s some water infiltration and that’s a problem so it’s really important that we get at it, soon."

Mullins says the longer the church is closed, the more expensive it will get to reopen it.

In December, Mullins provided a second update on their efforts, and at that time, he told the congregation it would cost $20 million.

"People ask me every week, you know? What’s happening? Are we going to be able to restore it? There’s such a great desire to preserve this building. It’s going to be a real trick converting that huge desire into huge dollars," says Mullins

Back in December, the Bishop of the Diocese of London, Ronald Fabbro, committed to spending $1-million on the project.

"There's been some false starts with regards to the diocese to try to restore the church," admits Mullins, although he adds he's hopeful this time will be different. 

Two previous community-driven fundraising initiatives in 2012 and 2013 were both unsuccessful.

Bishop Fabbro suspended the campaign in 2012 after years of conflict and $450,000 in losses split equally between the diocese and the non-profit group Assumption Heritage Fund, which helped manage the campaign.

A second fundraising effort failed in 2013 and a $10-million anonymous donation was pulled off the table over due-diligence concerns.

"It’s been a lot of work to do to be able to clarify what went wrong in the past when they made prior attempts to restore the church, and hopefully we don't end up in another blind alley," says Mullins.

Mullins adds he is finishing up a third update on the project, including the financial cost and potential timelines, which he plans to release to the public in "a week or two."