Cleaning and Restoring Rusty Metal
Regardless of which method of rust prevention you choose, proper preparation is the key to success. Approximately 80% of all paint failures is due to improper surface preparation so this step should not be overlooked unless you want to keep doing this over and over.
Remove rust from the metal surface:
Rust is like a cancer that eats away at your metal items. As rust forms on metal, the actual metal itself is being eaten away. Left unchecked, it will eventually destroy the metal beyond repair. To prevent this the surface of the metal object must be cleaned of all loose and flaking rust and paint. Here are several methods that can be employed:
- For smaller items such as rusted tools or cast iron pots, try using white vinegar. The vinegar reacts with the rust to dissolve it off of the metal. To use, soak the metal in white vinegar for a few days and then scrub the rusty paste off. Repeat if necessary.
- If vinegar is not completely removing the rust, you can use a chemical remover. Many different types of chemicals can be purchased to help dissolve rust. They are typically made from phosphoric or oxalic acid and can be harmful to bare skin. Always take precautions when using a chemical to dissolve the rust. Follow the directions for your rust-removal product, as application may vary between products. These chemicals often need to set for a long time and require scrubbing afterwards, so be ready for a little extra work. These products can be expensive and only work for small-scale projects.
- Convert the rust. Purchase a rust converter which works to stop rust from eating away any more of the metal. It is similar to a spray paint, and acts as a primer for a coat of paint over the top as well. This can be purchased at your local hardware store and is often labeled as rust convertor, rust treatment or rust reformer. Although this stops rust from expanding, it may not be as effective as completely removing the rust from the metal. This is only an option if you plan on painting over the metal. It will also leave a rough texture under the paint, as you are essentially just adding a covering to the rust.
- For larger metal pieces, sandblasting is often the easiest, quickest way to remove old paint and rust from metal. Compressed air at high pressure is used to blow fine sand or other abrasive material through a hardened spray nozzle and quickly "blasts" away whatever the blast material hits. Sandblasting is ideal for deeply carved wood, metal or brick surfaces, ornamental iron work and hard to reach areas. While small handheld units are available for small jobs like tools, wrought iron handrails, and outdoor furniture, specialized equipment, such as a compressor and protective gear is also required and often it is easy to pay a professional to sandblast your item, rather than doing it yourself.
- If you don’t have access to a sandblaster, you can always simply sand down the item until the rust is removed. You can sand the item by hand, or you can purchase a sanding attachment for your power drill. Be sure to put some elbow grease behind your work, because you don’t want to leave any spots of rust to spread. Start with a hand held wire brush or a wire wheel brush for your drill to knock off the main areas of rust. Normally a few quick passes will remove the loose material. Then the wire brushing should be followed up with a complete sanding until the metal piece is smooth and free of defects. Normally a rough sanding with 80 grit sandpaper followed by a smooth sanding with 120 grit does an adequate job.
Next the surface must be cleaned and degreased, paints and coatings do not bond well to dirty or greasy surfaces. A washing with a strong detergent followed by a through rinsing is required. The light "flash rust" that appears after washing can be removed with a cloth dampened with paint thinner or one of the commercial "surface prep" materials available.
Priming and Painting:
At this point if you are not going to paint your metal item, you can coat the metal with a simple oil or grease like WD-40, a good application for something like gardening or hand tools.
If you are going to paint your item, it should be primed with a rust inhibiting primer and finished with two coats of a quality exterior enamel. Spraying is quite acceptable but I strongly recommend that the primer be brushed or sprayed and worked into the surface with a brush while still wet. Spray painting alone will not get the paint down into tiny pinholes and crevices but will only "bridge" these areas resulting in premature failure as the moisture and oxygen will attack the exposed steel.
Modern paint chemistry now allows water base paints to be produced which have fantastic rust inhibiting properties and I highly recommend them over solvent base. Besides being low odor and easy to cleanup, an added advantage to water base paints is their ability to melt in with any trapped moisture which may not be visible to the naked eye. These coatings will force the moisture up to the surface and replace it with rust proof chemicals that seal the surface off. You will see rust looking spots in your dried primer but do not be concerned, most can be wiped off with a cloth as it is nothing more than rusty moisture that has been forced to the surface.