Regular facade cleaning is essential for maintaining the value of an object. In particular cleaning of porous facade materials (e.g. plaster, concrete) is challenging because stubborn soils often penetrate deep into these construction materials and become embedded in the porous structure.

The main causes for soiling of facades are ubiquitous industrial and traffic-related emissions as grease- and oil-like substances or diesel soot. Grease- and oil-like substances wet the surface of the facade materials and form a firmly adhering, sticky film (primary soiling), which promotes the accumulation of further dirt components (secondary soiling, e.g. soot).

Nutrients and humdity contained in soil also promote growth of moss and algae or mold infestation of facades (secondary microbial infestation). Since stubborn soiling penetrates particularly deeply into porous facade materials, it can often only be removed with great effort and the use of large quantities of cleaning chemicals.

Quasi liquid coating systems for generation of oil and water repellent surfaces on porous facade materials were therefore developed. Such quasi-liquid coating systems are based on trifunctional polymers, consisting of a polydimethylsiloxane (PDMS) group and a solvophilic covalently crosslinkable substrate affine group.

In aqueous solution, the trifunctional polymers form association colloids by aggregation of the PDMS groups, whereby the solvophilic covalently crosslinkable substrate affine group shield the PDMS groups from aqueous phase and provide high water solubility of the colloids.

After application, association colloids accumulate on facade surface during drying process. Due to the inversion of polarity at the interface (water to air), the subsequent opening of the association colloids occurs with the formation of a layer of aligned PDMS chains on the surface of the porous facade material.

Covalent bonds between trifunctional polymers and components of the facade material lead to high adhesion and stability of the quasi-liquid coating system formed in this way. The high mobility of the aligned PDMS chains of the quasi-liquid coating system ensures that even liquids of low surface tension are repelled by coated porous facade materials and slide off.

This can significantly slow down the soiling of coated facades. The continued good wettability of the quasi-liquid coating systems by water also enables simple, fast and gentle aqueous cleaning of coated porous facade materials.

The research report is available on request from FRT.