The Zep Commercial mould & mildew stain remover is a ready-to-use, professional strength formula that quickly dissolves stains caused by mould and mildew. It uses the power of bleach to safely whiten surfaces, such as fibreglass, tiles and grouting. It can be used both indoors and outdoors but works best in bathrooms and kitchens where it is most humid, says Zep. It can be used on toilet bowls, sinks, baths and surfaces such as ceramics and acrylic. The product is currently stocked in Screwfix stores and online.