Rust attacks most outdoor metal surfaces, from sheds and patio furniture to grill stands, iron gates and railings, and steel mailboxes. Painting those surfaces is one of the best ways to protect them from the water and oxygen that cause rust. But doing it properly–so the rust doesn’t return–can be tricky and requires thorough surface preparation and the right coating.
Begin by removing loose, flaking rust with a wire brush or a wire drill attachment. This can take time but it’s important you work down to bare metal so that every trace of rust is gone. If that’s not possible, and it rarely is, any remaining traces of rust should be chemically neutralized with Benjamin Moore’s P82, the Super Spec HP Rust Converter. This coating forms a film that converts the rust into a black, inert, non-corrosive iron complex that’s good to accept paint. After four hours, the metal is ready for the next coat.
For the finish coat, use one of several Benjamin Moore Direct-To-Metal (DTM) products. These are available in both Alkyds and Acrylics versions and in many sheens. The most important thing to know is that you must apply multiple coats because each coat of paint contains pin holes that will allow moisture to reach the metal and cause rust. Benjamin Moore’s Alkyd Low Lustre (P23) and Alkyd Semi-Gloss (P24) combine primer and top coat in a single product. Bare metals need two coats; but with a previously painted surface you may be able to get away with one.
If you’re looking for a glossy finish, consider Benjamin Moore P22, a Urethane Alkyd Gloss Enamel. This finish is best over an alkyd primer, like BM product P06, the Super Spec HP Alkyd Metal Primer. A coat of P06, which also contains rust-inhibitive chemicals for long-term corrosion protection, prepares any ferrous metal surface for the top coat. In fact, once you’ve applied P06, you can opt for the glossy enamel P22 or even choose an acrylic finish, if you prefer.
Benjamin Moore also makes DTM’s in acrylics. These can be used on both ferrous metal and well as galvanized and aluminum. For those surfaces, the primer to use is Benjamin Moore’s P04, a Super Spec HP Acrylic Metal Primer. An alkyd product applied on a galvanized surface will fail. But hopefully those surfaces aren’t showing much evidence of rust–the purpose of galvanizing is to limit corrosion in the first place. Acrylic DTM’s such as Benjamin Moore’s Super Spec HP® D.T.M. Acrylic Low Lustre P25 or Super Spec HP® D.T.M. Acrylic Gloss Enamel P28 are great choices for properly prepared ferrous and galvanized metal surfaces. All of these coating are available in any Benjamin Moore color so your options are endless. Choosing the correct product for your project is essential. For instance, for a surface that takes a lot of abuse like metal patio furniture or an exterior Bilco door opt for the stronger Alkyd products. For your galvanized metal surfaces or areas such as the mailbox, gutters, and downspouts, take advantage of the easy soap and water clean up of an Acrylic DTM.