Enhancing the durability of historic brick masonry: The role of diammonium phosphate and chitosan in reducing salt-induced damage

• Brick samples were treated with DAP alone and with DAP followed by chitosan. • The treatments did not alter the water transport properties of brick. • Treated and untreated samples were subjected to the Wick Test in sodium sulphate . • The amount of efflorescence and material loss were evaluated. • The treatments favoured the formation of efflorescence and decreased salt-induced damage. Salt crystallization represents a serious threat to historic architecture worldwide, causing structural and aesthetic damage due to the accumulation of salts in porous building materials, such as bricks. Historic masonry is particularly vulnerable to this type of damage due to the complex interactions between salts and its porous matrix. Salt crystallization modifiers have proven to be valid candidates in reducing the detrimental effects of salt crystallization within porous materials, thereby prolonging the lifespan of historic structures. In this research, chitosan was selected as crystallization inhibitor, considering his remarkable properties in terms of sustainability and cost-effectiveness. Applied to brick samples in combination with a phosphatic treatment based on diammonium phosphate, it resulted an encouraging new solution to reduce salt crystallization damage without affecting the material's properties and hence showing a good compatibility, although further research is needed to assess the effectiveness of the chitosan-based treatments for in-the-field applications.