I believe that stones eroded past a certain point were identified in the survey of the facade. The face of these stones was then raked back to form a key, and are currently being built up again in a coloured mortar mix. Something similar was done to Leinster House a few years ago. Apparently it is accepted conservation practice, but one wonders about the long term durability of such repairs.Cutting in stone indents would give a patchier appearance in the short term, but might be less risky in the long term.
On a similar topic I' ve noticed that the balustrades on the curved walls on either side of the Municipal Gallery have been painted over the last few weeks. My recollection is that these were of limestone, but I could be wrong. Hope it' s not just a misguided tart-up for the Bacon exhibition.