Dampness penetration problems in granite buildings in Aberdeen, UK: Causes and remedies

Many of the buildings in Aberdeen constructed prior to the mid 20th century are constructed of granite. The impermeable nature of this stone puts heavy demands on the performance of bedding and pointing mortars and affects the nature of penetrating damp problems. The particular dampness problems associated with granite buildings, especially with gable walls was investigated by case studies and a questionnaire survey of building professionals. While a variety of defects contributed to investigated damp problems, a high proportion were found to be involve mortar performance issues and decayed mortar debris blocking void spaces. A relatively high proportion of practitioners reported problems caused by incorrect specification of mortars and had encountered problems that originated at the time of repointing of buildings. A significant minority were of the opinion that the use of power tools for raking out joints contributed to debris build-up in voids. On granite gables the demands placed on mortar performance are particularly severe since the mortar has to do all the work in dealing with moisture movement. Many of the penetrating damp problems encountered in granite buildings can be attributed to debris dislodged by the use of power tools in raking out of joints, loss or removal of harling (rendering) and to incorrect specification of pointing mortars.