Cracking in Cornice

Q In India for restoration works of a 19th century palace, we had broken part of cornice band for roof repairing. Now after five months I am seeing few hairline cracks in the cornice. The cornice is made of bricks which are corbelled out and are plastered with lime brick dust, sand mortar.

A Plasterers often tell me that it’s normally not the plasterwork that fails but movement in the backing to which the plaster is applied. Do you know why the cornice was originally damaged – could it have been movement in the corbelled brickwork, which is still moving? Another possible cause is shrinkage caused by using the plaster too wet.