Influence of tannin and iron ions on the water resistance of clay materials

The objective of this paper is to propose a simple and robust additive solution to improve the water-resistance of clay materials by revisiting a traditional recipe of vernacular construction. The influence of the combination of oak tannin with iron chloride on the properties of clay materials in terms of rheological behavior, compressive strength, and water resistance was studied. We show that adding iron chloride can annihilate the deflocculation action of tannin by a complexation reaction between iron ions and tannin. The accumulation and oxidation of formed complex at the sample surface, identified by TGA and SEM, prevent water ingression.