Only one site in the Derry City and Strabane District is known to have been affected by concrete blocks containing the notorious mineral ‘muscovite mica'.
Members of Derry City and Strabane District Council's Environment and Regeneration heard on We needy ù that a short desk top investigation by local authority building control officers had more or less given the district the all clear.
'Mica' has played havoc in neighbouring Donegal where pattern-cracking in walls in which concrete blocks containing the mineral had been used, affected over a thousand homes.
A report to the committee this evening advised the properties affected had all been built using blocks manufactured by a single concrete products supplier in Donegal.
But at least one social housing estate in Derry and Strabane is also known to have been affected, it was revealed.
The committee heard: "Building Control understand that blocks were supplied to one social housing site in Derry from the Donegal based concrete products manufacturer implicated in the mica affected concrete block problem.
"It is understood that when this matter became apparent, samples of the concrete blocks on the site where taken for laboratory testing.
"The consulting engineer advising the developer was content that the test results, while confirming the presence of some muscovite mica within the test samples, indicated that the level of this mineral in the blocks was below the recommended maximum value and should therefore, be satisfactory for use."