Two areas of possible rising damp issues here;
After scrapping off the loose paint and efflorescence salts, sealing the area with Zinsser Gardz (sealant and Alkali resisting primer) and Zinsser BIN (shellac sealant paint) and then two coats of emulsion. This paint system should prevent the issue from coming back. The Zinsser Gardz bonds any friable suface and the Zinsser BIN will block any damp coming through. Breathable emulsion will allow for any moisture on the surface to evaporate keeping the damp at bay.
