True rising damp occurs where groundwater moves up through porous masonry lacking an effective damp proof course. Far more often the cause is raised external ground levels, defective rainwater goods, cement render or blocked sub-floor ventilation.
Diagnosis matters because the remedies differ completely. Chemical injection into a wall whose real problem is a path built up above internal floor level will not solve anything.
Start with the simple external causes: ground levels, gutters and downpipes, gullies, and whether cement render or concrete paths are trapping moisture in the wall base.