Smartseal Rust Remover is effective for dissolving problematic rust stains caused by iron-containing fertilizers, metal garden furniture, leaking heating systems, etc on natural stone and concrete surfaces. It can be used externally on patios, driveways and walls as well as internal surfaces if necessary. The fast-acting formulation will start to work straight away after application as it starts to attack and neutralise any rust stains present. Within minutes the powerful chemical formula creates a purple coloured reaction where the rust stains were so you can see the rust remover working. The acid-free formulation is PH neutral and will not damage the natural stone or concrete after application.