Façade coatings containing organic binders often include biocides to prevent microbial growth on the surface. This study uses a vertical sprinkler system (SPS) to investigate biocide leaching from organic paints and renders, focusing on the substances octylisothiazolinone (OIT), diuron (DCMU) and terbutryn (TBY).

The time-resolved, cumulative emission of the biocides suggests a diffusion-controlled release process, which can be further affected by apparent saturation of the water phase due to distribution equilibria. It was found that this process can be influenced by the specific amount of contact water (h_p) especially for highly emitting renders.

Increasing h_p from 14 to 25 L m^-2 resulted in higher biocide loads in the leachate, leading to leached biocide loads between 97 and 176 mg m^-2 for DCMU, between 52 and 345 mg m^-2 for OIT and between 23 and 176 mg m^-2 for TBY.

The results of the SPS leaching tests were compared with those of the leaching test according to the standard test procedure DIN EN 16105. In SPS leaching, the OIT loads were 14% to 120% higher, and the TBY and DCMU loads were up to 50% higher, compared to the DIN EN 16105 results under similar conditions, such as h_p and duration. This indicates better surface wetting by the SPS method, thus mimicing realistic leaching conditions. These results call into question the adequacy of standard DIN procedures in reflecting practical biocide release conditions.

This study also demonstrates the possibility to apply wind pressure during leaching tests using the SPS method. No impact of 200 Pa overpressure (wind speeds of approx. 40 miles per hour) on biocide emission was observed for two exemplary samples.