ANALYSIS AND PREVENTION OF EFFLORESCENCE ON BRICK MASONRY PT.1. SOLUBLE SALT EXTRACTION

An alternative procedure to that proposed in EN 772-5 for the determination of soluble salts in fired clay brick was investigated, to take account of pH changes induced by mortar hydration. Crushed brick was shaken with water of neutral pH, pH 9.3 and pH 11.5, for time periods up to 180 h. Potassium, sodium, calcium, magnesium and sulphur contents of the water were determined by spectrophotometry. In basic pH media, potassium, sodium and magnesium exhibited a rapid dissolution step, followed by slow and regular dissolution, attributed to alkaline attack of the silicate phase of the brick. The main source of calcium and sulphate ions was residual anhydrite. A two-step dissolution mechanism was observed, which increased with increasing pH. 4 refs.