Reading about the cleaning work on the Malmaison Hotel, the old Aviva building (Extreme cleaning underway to transform landmark York building, February 16) reminded me how many years ago, in an attempt to smarten up York Minster, they set to work and sand-blasted a section of stonework, only to find out later that the soot and other pollutants were effectively waterproofing and protecting the building.

It is to be hoped that the cleaning work on the Malmaison doesn’t expose the building’s outer skin to the corrosive effects of the elements.

DM Deamer, Penleys Grove Street, Monkgate, York