Effect of hydrophobization on the properties of lime–metakaolin plasters

Mechanical, hydric and thermal properties of lime–metakaolin plasters hydrophobized by zinc stearate added to the fresh mixture are analyzed in a wide range of hydrophobe dosage. The water absorption coefficient of analyzed plasters is found to decrease very fast with the increasing zinc stearate content in the mix, while both the compressive and bending strength decrease only moderately. The open porosity, water vapor diffusion properties and thermal properties are affected positively by the addition of zinc stearate. Taking into account the mechanical, hydric and thermal properties, together with the economical factors and recommendations of the supervisory authorities of architectural heritage on the properties of renovation renders, the lime–metakaolin plaster with the zinc stearate amount of 1% of the mass of binder can be considered as an optimal solution.

► Zinc stearate in a wide dosage range is used as hydrophobe added to the fresh lime–metakaolin plaster mixture.
► Water absorption coefficient decreases very fast with increasing zinc stearate content.
► Compressive- and bending strength decrease related to the hydrophobe use is only moderate.
► Open porosity, water vapor diffusion properties and thermal properties are affected positively.
► Lime–metakaolin plaster with the zinc stearate amount of 1% of the mass of binder is an optimal solution.