Biotreatment of ceramic bricks: The impact of the application method of an innovative bioproduct on biomineralization

The effect of biological treatments on protection of exposed construction materials in the built heritage may have great potential. This work reports the efficacy of several techniques (dropping, spraying, brushing, poulticing and absorption by capillarity) to apply a new bioproduct, produced by Escherichia coli cultures supplemented with iron, aiming to treat the surface of ceramic bricks. The results showed that most biotreatments improved the ceramic bricks resistance to water absorption, depending on the method of application of the bioproduct. Nevertheless, within the error range, the most efficient biotreatments were observed when the bioproduct was applied by dropping, brushing and spraying. The bioproduct analyzed in the present study can be stored and easily transported to construction sites, where it can be readily prepared by resuspension of the dried bioproduct in tap water. The water resistance effect of the bioproduct was attributed to the presence of a gelatinous biofilm and to the formation of amorphous biosilica aggregates (biomineralization by biosilicification) that filled the pores and voids of bricks samples. Acting as a mild water repellent agent, it may be a promising solution for protection of ceramic bricks, reducing the degradation rate, namely for compatible and ecological architectural heritage conservation practices.