Konrad Fisher was an herectic against outside thermal insulation on walls with a rendering. According to him, all thermal insulation except (closed cells) cellular glass develops mold and other problems in the rendering, which make look the rendering dirty. The rendering has to be cleaned regularly or to be treated by harmfull and expensive fungicides. Bot operations have a large cost.
In his opinion, cellular glass, due to his closed cell structure is a much better alternative, which does not become wet and will not induce mold on the rendering. He explains everything in a YouTube movie, however in German.
He also mentions the price of cellular glass but he is clearly not aware of the new generation cellular glass from GLAPOR at 250€/m³. In this case, maintenance of the will be much lower, generating a payback for the cellular glass.
Above, you observe a dirty rendering due to mold and on the right the solution according to Konrad Fisher with cellular glass in his hands. These pictures can be found in the YouTube movie.