My well built garden wall has begun to show very severe corrosion of the mortar, in some places the mortar is deteriorated and leaving a gap at least 2" deep into the wall. The deterioration is not consistent throughout the entire wall but it is getting worse and worse. It has been built 12 years and was very well built in rustic brick.
In some places the mortar has crumbled, in others has shrunk away from the bricks leaving a 3 mm gap.
Any ideas as to what could have caused the mortar to deteriorate over a relatively short time?
The wall was built by a local firm who have also built us a house. The house has been rendered so we've not checked the mortar on this yet...