Consultant engineers have been called in to investigate serious cracks, one nearly 200 feet long, at the Great South Wall of Dublin Port.
The wall, which is a protected structure, was built in the late 18th century to protect the shipping navigation channel from the encroachment of the sandbank at Sandymount, and originally extended for more than three miles.
Described as one of the best-constructed breakwaters of its kind in the world, its granite blocks were ingeniously interlocked without the use of any bonding material. An Taisce has claimed that the cracks are due to the use of cement grouting on its stonework.
In 2003, the paved walkway leading out to Poolbeg lighthouse was grouted with cement, turning the surface of the wall into "a rigid, brittle plate", according to Kevin Duff, of An Taisce. As a result, dozens of original paving stones have been split in two.
He claimed that what is happening to the Great South Wall, which was completed in 1790, "is a stark illustration of the hazards of using cement on stonework, particularly historic stonework". Unfortunately, this was "still widespread throughout Ireland", he added.
Mr Duff said traditional structures built of stone or brick require "breathability" and are generally incompatible with hard modern cement.
Professional advice should have been sought before embarking on this kind of work to the Great South Wall, he said.
However, Jimmy Carolan, Dublin Port marketing manager, said there was no evidence that the grouting caused the cracks.
He stressed there was "no immediate danger of the wall falling into the sea". If that happened, it would be "disastrous" for the port.
"We're aware of the existence of the cracks, and we are taking it seriously," he said.
"We have undertaken a number of site investigations and engineering studies, and these will lead to a number of options that will be evaluated and acted on."
One of the myths about the wall is that it was built on foot of a survey of Dublin Bay by Capt William Bligh, of "mutiny on the Bounty" fame.
It was actually finished 10 years before Bligh's survey, which recommended a parallel wall on the north side.
The Great South Wall so changed the movement of water in the bay that it led to the creation of Bull Island, now a UN biosphere reserve.
