​To put it mildly, chemical damp proof courses in traditional buildings are a waste of money. If anyone suggests a traditional property needs one they simply don’t understand how old buildings work. This work usually involves injecting a liquid compound under pressure through pre-drilled holes. They advise that any plaster on the inside of the wall has to be removed up to a height of one metre, and then replaced by gypsum plaster afterwards.

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All of this highly intrusive work is expensive and will be unnecessary, and indeed often exacerbates the problem in due course. The proper way to address any damp issue is to understand the root cause of the problem first. In many cases, it will be caused by the fact that the internal floor areas are lower that the external ground levels, allowing water to penetrate. A simple French drain will solve the problem, often at little cost.

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Another common cause is how the building is used. If you allow sufficient ventilation by simply opening windows then condensation will not form. Modern buildings are meant to keep weather out through sealing them up, and by treating old buildings in the same way there will be inevitable consequences to the building and potentially to the occupant’s health.