PURPOSE: To apply a fungicide showing an effect in an examination in an culture medium containing the fungicide, an examination under sever conditions and an on-the-spot examination respectively using a sample fungus collected from wild fungi growing on a finished wall of an existing building to a new building.

CONSTITUTION: A wild fungus growing on a finished wall of an existing building is collected, cultured, identified and used as a sample fungus. A culture medium examination in PDA medium at a constant temperature and a constant humidity for 10 days using a filter paper having both the sides coated with an emulsion paint containing an objective fungicide, a sever condition examination at 85-95% humidity and 10-30°C for 10 months using a plasterboard coated with an emulsion paint, etc., containing the objective fungicide, an on-the-spot examination at 65-100% humidity and 5-30°C for 5 years using various finished materials containing the objective fungicide and other examinations are carried out in the presence of the above-mentioned sample fungus to select an effective fungicide. The selected fungicide is applied to a new building.