David Evans, 23, was struck by the slab of rock while helping to build a large wall at the £20m home of former Pizza Express boss, Hugh Osmond in Oxfordshire.
He was taken to the John Radcliffe Hospital by air ambulance on 9 February 2010 with catastrophic injuries to his chest and abdomen, but was pronounced dead later the same day.
His employer Cavendish Masonry was found guilty of corporate manslaughter yesterday by jury a at Oxford Crown Court and now faces a large financial penalty.
The court heard that the firm had committed a gross breach in its duty of care in its management and organisation of the work on Osmond’s 1,200-acre Well Barn Estate.