Not every damp mark comes from a leaking joint. When a cold surface is below the dew point of the surrounding air, water vapour can condense on it. This can occur around cold-water or cooling pipework in warm, humid conditions.
Identify the source of moisture
A sound diagnosis separates a leak, condensation and moisture arriving from the building fabric. The pattern of dampness, operating conditions and temperatures can help establish which mechanism is present. Replacing a fitting without that distinction may leave the actual cause untouched.
Costa del Sol properties can combine warm outside air with cooled interiors and technical spaces. Pipe routes through those spaces deserve particular attention when moisture appears around a ceiling, cupboard or plant area.
Make the insulation continuous
The appropriate protection depends on the system. For water-supply pipework, CTE DB HS 4 requires consideration of condensation and a protective separating element with a vapour-barrier function where it could damage the building; that element need not itself be thermal insulation. RITE has separate insulation requirements for thermal installations.
Before closing a void, inspect the complete run and repair damaged seams or missing sections. A tidy visible length of insulation does not prove that inaccessible junctions are protected.
Record and monitor
Photographs of the insulated run before it is enclosed can help with future fault finding. If staining has already developed, the affected material should be assessed and allowed to dry as appropriate before finishes are restored.
The aim is to control the moisture mechanism, not simply cover the stain.