The next best step might be to determine what type of damp-proofing course your building has. Its important as it affects greatly and remedial measures that may be necessary. I would be wary of any proprietary product offered by a 'specialist' builder, and especially wary of any offer of repairs accompanied by what may appear to be a useful long guarantee. You don't say how old your building might be.Its amazing how often what may appear to be a defective damp-proofing course is in reality no such thing, the problem of rising damp being entirely due to damp-course bridging - it might be that the external ground has advanced somewhat either be vegetation build-up or simply earth banking and that that is the cause of the damp, in which case the remedy is simply reinstating a healthy distance between the damp-course and the external ground level. The usual recommendation is a clearance of around 150mm or so.Hope this helps.
Clifford Cowell ● 2621d