Damage due to the crystallization of salts is a common problem in porous building materials. Also mortars used in the restoration of historic buildings are often subjected to a high salt load, resulting in a rapid degradation and high maintenance costs. Especially lime-based mortars, used for example as render, plaster, bedding mortar or pointing mortar, are vulnerable to this type of damage. Despite the extensive research efforts, no definitive solution yet exists to tackle the problem of salt decay in building materials. Existing solutions to improve mortar resistance with respect to salt decay such as modifying the moisture transport properties of the mortar (e.g. plaster with water-repellent properties) or increasing its mechanical strength of the plaster mortar (e.g. by using a different binder such as cement), often show compatibility problems and might cause even more damage to the to be restored (historic) fabric. Recently a new approach, based on the use of crystallization modifiers to alter the salt crystallization process, has been proposed. The aim of modifiers is to prevent or mitigate salt crystallization damage in building materials. Modifiers are ions or molecules that can keep the salts longer in solution (inhibitors), facilitate the precipitation of a certain crystal phase (promoters) and/or change the shape and size of the grown crystals (habit modifiers). These effects are often present in combination, i.e. a promoter or inhibitor can at the same time act as habit modifier. @en