There are two main types of efflorescence*. The primary efflorescence is due to the development of calcium hydroxide during the hydration of cement and its migration to the surface due to the evaporation of access water.
The secondary efflorescence is given by the wetting of a mortar or concrete and the dissolution of the Portlandite present in the pores.
Due to the rather slow reactivity of metakaolin with Portlandite, the primary efflorescence can partly be reduced
but the secondary ones can be avoided by the use of sufficient metakaolin to convert the Portlanditeinto binder
(about 20% cement replacement).