Most chimneys used in the UK were originally designed and built for use with solid fuel. These chimneys were not particularly efficient or well insulated.

Inadequate insulation and oversized flues causes condensation within the chimney. This combined with the products of combustion produce sulphuric acid.

The sulphuric acid attacks the masonry/brickwork within the chimney and eats into the mortar causing joint leakage and eventually the total collapse of the chimney-stack