I live in an 1866 stone built house and have a basement under one of the rooms. This has stonewalls with flagstone floors. I intend to use the basement for recreation use. The walls and floor are dry to touch but when I store items in certain areas of the basement mould appears on them. In other areas of the basement it is OK. I assume this is dampness in the atmsophere through one or more of the walls. Would a damp proof coating on the walls solve this?