Blown plaster and damp patches before redecorating

Sound the wall first

A knuckle or a small tapping tool maps the failed area quickly. The hollow zone is nearly always larger than the visible stain, and the repair has to extend to sound plaster on all sides.

Identify the moisture route

Rising, penetrating and condensation damp look similar on a decorated wall but need different remedies. Tide marks near skirtings, isolated patches at height, and cold-corner mould each point in a different direction.

• Low tide mark: rising or bridged DPC
• Isolated high patch: penetrating damp or a leak
• Cold corners: condensation

Hack off and re-plaster where needed

Where the plaster has blown, it comes off back to a sound edge and the wall is re-plastered, allowed to dry, then mist-coated. New plaster needs a thinned first coat to bond properly.

Decorating new plaster

Fresh plaster carries a lot of water and remains alkaline for weeks. Coating it too early traps moisture and causes patchy sheen and later peeling, so we schedule it around a realistic drying period.