Time and the elements are taking their toll on the Martello Tower that has guarded Saint John's harbour since the War of 1812.

Water has penetrated the stone walls of the historic military building and Parks Canada is determined to find out where it is coming from.

"We have to treat these places like treasures and preserve them," says Andrew Fry of Parks Canada.

Andrew Fry

Andrew Fry of Parks Canada says Martello towers like the one in Saint John are a national treasure and need to preserved. (CBC)

"We consider this an important piece of this story of Canada, about how we came to be, and the important events that shaped our country."

The Carleton Martello Tower in Saint John is a National Historic Site, one of nine still remaining of the 14 built in Canada in the late 18th century and first half of the 19th century. Five of the round defensive fortresses were built in Halifax, while Kingston, Ont., and Quebec City each had four.

The Saint John tower's walls are now shrouded in tarps and staging. The thick, stone walls have started to bow outward in some places.

"There's moisture that's getting in to the masonry, washing out the lime, and as a result it's crumbling.," said Fry.

Crews have been taking core samples from the walls of the tower. They are trying to determine exactly where the water is coming from.

"We wanted to better understand just how much this moisture in the walls is affecting the tower," said Fry.

Inside the tower, mineral buildup from dripping water has created a cave-like environment.

One possible source of water may be the cement lookout that was built on top of the original structure during the Second World War. Of the nine Martello towers still standing in Canada, the one in Saint John is the only one with such a structure built atop it.

Martello Tower top

This cement lookout was built on top of the Martello Tower in Saint John during the Second World War. (CBC)

"As far as I know they don't have the water infiltration issue to the extent that this one does," said Fry.

However, he said it's too early to draw conclusions.

The current work by Parks Canada is two-fold, he said.

"It's a quick fix for some of the severe areas, but the main piece of the work that's going on right now is an investigation."

Expert mason Bill Quinn has tested each brick in the tower, taking core samples 72 inches (182 centimetres) into the original stone walls. All the data will be incorporated into a report that will be forwarded to the federal government.

"Whenever they decide to do the work later they'll know exactly what's here," said Quinn. "They won't be going in blind."