Painting Metal the Right Way

Tips for choosing and using the right finish for your metalworking projects.

When properly painted, any metal can glisten like gold. But without the finished look that paint imparts, a welded project can look like a mass of rough, bent steel. Whether your goal is to revitalize a rusty handrail or create a one-of-a-kind hotrod, knowing what paint to use (and how to apply it) is the key to creating metalworking projects that shine.

Choosing paint
Although aficionados hotly debate what type of paint is best, in most cases your decision will be determined by the type of metal object you’re painting, how it will be used and in what environment it will reside. To make the right choice, you’ll need to understand these terms:

Acrylic: A component of paint rather than a type of paint, acrylic is a synthetic polymer resin that is used as a binder and forms a hard, durable, plasticlike coating.

Alkyd: Also referred to as “oil-base,” this type of paint is one of the best choices for use on exterior metal surfaces.

Latex: Perhaps the most common type of paint, latex is a water-base paint that can yield good results on metal surfaces, but because it dries to a porous finish (which can allow moisture to penetrate to the metal surface), it should only be used over primer.

Lacquer: Because its solvents are toxic, traditional lacquer paint is seldom used today – in fact, it is illegal to use it as a bulk spray in many states. However, far less toxic waterborne lacquers are available in spray cans for small-scale home projects and auto-body repairs.

Though traditional lacquer is unavailable in large quantities in many parts of the country, you can buy individual spray cans of waterborne lacquer for small-scale automotive applications.

Enamel: This generally refers to a hard, durable, high-gloss paint that holds up well in harsh environments. Although the term enamel is traditionally used to describe oil-base products, latex enamels are now available, and easy-to-use spray enamels are commonly found in hardware stores.

Urethane: These paints are usually solvent-base, although some waterborne urethanes are also available. (Don’t confuse waterborne with water-base; waterborne paint is derived from solvents that are reduced with water to decrease the amount of volatile organic compounds [VOCs] they contain, whereas water-base paint contains no solvents.) Urethane paints (such as PPG’s Deltron and House of Kolor’s Kosmic Kolor) are very common in the automotive industry and produce a rich, durable finish.

Epoxies: A two-part system consisting of a resin and a hardener, epoxy is exceptionally durable and resists environmental degradation. Though they’re most commonly used in the aircraft industry and as floor coatings, epoxy finishes are ideal for any metal surfaces that are exposed to harsh conditions.

Delivery methods
How you apply paint to metal greatly depends on the type of paint you’ve decided to use. Although some paints are available in a variety of forms, others can be bought only in bulk. Typical delivery methods include:

Brushes: As a paint delivery device, brushes work well for many applications. To achieve optimal results, always use a high-quality brush with bristles suited for the paint you’ve chosen. Though there are exceptions, in most cases a nylon/polyester (synthetic) brush is best for water-base coatings, and a natural-bristle brush is preferable for oil-base coatings. (Natural bristles absorb water; when used with water-base paint, they become water-logged and difficult to work with.)

Spray cans: Perhaps the easiest way to paint metal, ready-to-use spray cans of enamel, lacquer or latex work well for small to medium-size objects. Remember to work in a well-ventilated area with low humidity and an air temperature between 50 and 85 degrees.

Guns: If you’re planning on painting a larger project such as a car or motorcycle bodywork, you’ll have to use a spray system. You can choose from three variations:

  • A compressor with a standard gun — An air compressor delivers pressurized air to a gun to atomize paint and apply it to the work surface. Depending on the type of gun, the high-pressure air will either siphon the paint up from a bottom-mounted cup (known as “siphon-feed”) or accept it from a cup mounted above the gun (known as “gravity-feed”). Standard guns have been around for decades and are relatively easy to use, but because of their air-pressure demands, they create a lot of overspray, and as a result many regions are banning their use because of the potentially harmful VOCs that the overspray releases into the atmosphere.
  • A compressor with a high-volume, low-pressure (HVLP) gun — This system uses a compressor and a specialized HVLP spray gun to deliver a higher volume of paint to the surface. As a result of the lower air pressure, more paint adheres to the workpiece, resulting in much less waste through overspray.
  • A turbine-driven HVLP system — These easy-to-use setups, which consist of a spray gun and a turbine system that replaces the air compressor, are a great investment if you don’t want to buy a compressor. And because they don’t rely on a compressor to generate pressure, there’s far less chance of accidentally delivering water or oil to the workpiece (a problem that can result in paint blemishes).

A turbine-driven HVLP system does not rely on an air compressor. Instead, multiple turbines create the pressure needed to deliver the paint onto the work surface.

Typical spray-gun components

Applying paint
No matter which delivery method you choose, the painting steps are basically the same. (The exceptions are specialized automotive finishes, which may require you to add reducers, retarders and hardeners. It’s essential that you closely follow the manufacturer’s instructions to achieve optimal results.)

Start by preparing the work surface. Clean bare new metal with denatured alcohol to remove any oil residue. If the metal has previously been painted, scrape off any loose or peeling paint. Be sure to wear eye protection, a dust mask and work gloves, and remove as much loose material as possible. Treat any mildew with a 3:1 mixture of water and bleach; then scrub the work surface with a detergent such as Simple Green and rinse thoroughly. Dry the surface and use a tack rag to remove any small particles.

Next, you’ll need to apply primer. Don’t be tempted to skip this essential step: Primer creates the bond between the topcoats and the underlying metal and protects the metal from corrosion. Even if you plan to use what’s referred to as a “direct-to-metal” latex topcoat, which in theory doesn’t need primer, you’ll still achieve the best results if you prime the surface first.

The type of primer you choose depends on the work surface. Follow these guidelines:

  • If the workpiece is bare steel, apply two coats of alkyd primer to achieve the best corrosion protection.
  • Apply an alkyd primer if the workpiece was coated with an oil-base paint; use a latex primer for latex-painted surfaces. (As a general rule, alkyd finishes won’t take well to latex, but you can apply latex over an alkyd finish.)
  • If the workpiece is copper, brass or another copper-containing alloy, use only a primer recommended for these materials; otherwise the finish coat may discolor.

When applying the paint, follow the manufacturer’s recommendations. Don’t cut corners — you’ll likely end up with disappointing results. Take your time, work carefully and allow ample drying time between coats. The extra effort will result in a sense of pride and a finish that lasts.

Be Creative Whatever type of finish you envision for your project, you can probably find a spray paint to create it. Specialty spray paints such as Rust-Oleum’s Hammered Finish (which creates a unique hand-hammered look), Plasti-Cote’s Fleck Stone (which duplicates the look of carved granite) and Krylon’s Looking Glass mirror paint (which creates a highly reflective surface) are just some of the creative options for metal projects. Or take a cue from the automotive industry and try Dupli-Color’s Mirage (shown here), a prismatic spray paint that changes color depending on how light hits it. Creating a prismatic color-changing finish once required a spray gun and very expensive paints, but now DIYers can easily achieve the same look with spray kits.

This project is part of HANDY's Top 5 Collection: Painting Tips.
Click here to check out the other four painting articles in this collection.