Cemex UK, owners of the Rugby Cement brand, have been fined £20,000 after homes, businesses and vehicles in Warwickshire were covered in dust.
The dust from the Rugby Cement plant in Rugby was found at properties up to two miles away in March 2007, after escaping from a silo.
The case was brought by Environment Agency, which had received nearly 100 complaints.
Cemex UK admitted breaking their permit conditions; they were also ordered to pay £13, 500 in costs.
In a statement a spokesman said the dust was unlikely to have caused anyone any harm but apologised for the inconvenience caused.
In 2006, Cemex were prosecuted by the Environment Agency and fined £400,000 after homes in Long Lawford, Warwickshire were covered in clay and sand particles.