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A guide to primers and paints for rust-free steps

by Jeanne Huber, The Washington Post | June 5, 2021 at 1:42 a.m.

Q: The front steps to my otherwise perfect house are wrought iron. Over the past 25 years, they have been sanded and painted every two to three years, only to rust after eight months. Can the staircase be covered or coated with something better than paint? If paint is the only option, are there any new products that work better than Rust-Oleum?

A: First, Rust-Oleum is a brand, not a specific paint product. Although the brand's widely available Stops Rust paints are best known, it also makes a range of heavier-duty products sold as industrial coatings. If you haven't been meticulous in following the preparation steps recommended for Stops Rust, going through all the steps might be one solution. Or you might want to switch to an industrial coating from Rust-Oleum or a different company, but these coatings are trickier to apply and are usually used by professionals.

There's also a chance that you are experiencing an especially bad rust problem due to the material used to create your steps. Steven Painter, brand manager for Burke Industrial Coatings, looked at the pictures you sent and asked whether your steps are made of a product called CRS (cold rolled steel) diamond plate. "Many times, that material has had a treatment which generates a black oxide layer," he wrote. "We can usually coat over this successfully but it is something to mention." (His contact information, if you need to pursue this, is on Burke's website, burkeindustrialcoatings.com.)

Also, if the steel on your steps was galvanized, the paint you've been using may not be suitable. Some paints for metal work well on galvanized surfaces; some don't — including Rust-Oleum's Stops Rust Protective Enamel (both the spray and brush-on formulas) and its Rusty Metal Primer. Nuances like these may not be prominent on product labels, but you will find them in the fine print or on the data sheets available from manufacturers' websites.

INDUSTRIAL-TYPE COATING

If you want to upgrade to an industrial-type coating, Mark Wilgen, senior director of marketing for the small project paints team at Rust-Oleum, listed three industrial options from his company: He labeled Rust-Oleum's 7400 System Alkyd Enamel as "good," its 9100 Epoxy Mastic as "better" and its 9800 Urethane Mastic as "best." The 7400 alkyd isn't suitable for use on galvanized steel, though, while the other two are OK.

Rust-Oleum's website, rustoleum.com, says all three industrial coatings have a "two-year rust-proof guarantee," while the product overview for Stops Rust doesn't specify a time, just that it provides "excellent" protection against rust.

Paints that protect steel from rusting typically work by sealing off the metal from water, corrosive materials (such as de-icing salt) and oxygen. But no coating seals perfectly over the long term, so the paints also contain rust inhibitors. The original paints included zinc to act as a sacrificial oxidizing material. Whatever would cause rust instead would react with the zinc. Paints with zinc as the only rust safeguard are still sold today, but they come only in gray. Other ingredients, many of which are trade secrets, allow rust-preventing paints to come in other colors and still keep rust away, at least for a time.

'LIQUID STAINLESS STEEL'

There is another category of rust-preventing coatings for steel that might be worth exploring for a project like yours. These are formulated with minute flakes of materials that don't rust, such as mica or stainless steel. When mixed into coatings, the flakes wind up oriented mostly parallel to the surface. If you were to thinly slice through a paint layer and view it crosswise through a microscope, you would see the flakes stacked as if they were bricks on a wall, Painter said. Burke Industrial Coatings also makes epoxy finishes with stainless steel flakes, also known as "liquid stainless steel." Just as with bricks on a wall, where the mortar joints never line up vertically from row to row, so moisture can't cascade down the mortar joints, the stainless steel flakes force anything that seeps through the epoxy to take a circuitous route to the steel underneath. The route can have so many bends that it effectively becomes a dead end, thus preventing the steel from rusting. And unlike depending on zinc to prevent rust, the protection doesn't wear out unless the paint wears or falls off.

Whatever coating you choose, preparation is key. First, thoroughly clean the steps. Then get rid of as much rust as possible by sanding, scrubbing with a wire brush or using a drill or metal grinder outfitted with a wire brush. (Wear goggles.)

"If any rust is remaining when coated with paint, the rust will continue to expand under the coating and eventually attack the coating from the back side," Wilgen said. If you can't get off all the rust, though, you can slow its reappearance by priming with an appropriate primer. If you plan to repaint with Stops Rust, the right primer for a still-rusty surface would be Rust-Oleum's Rusty Metal Primer ($9.98 a quart at Home Depot) or an automotive primer, such as Rust-Oleum's Automotive Filler Primer ($31.82 a quart on Amazon). Over the primer, you'd apply two coats of the Stops Rust Protective Enamel ($9.98 a quart at Home Depot).

INFLUENCED BY PRICE

Rust-Oleum's industrial coatings are listed as DTM (direct to metal), but still use a primer. It helps the topcoat stick and stay intact, and, given all the work that's needed to prepare the steps for new paint, it seems silly to skip this coat. Identify the recommended primer by looking at the technical data sheet for the coating you choose — a decision that might be heavily influenced by price. Wilgen's good, better, best rankings of Rust-Oleum's industrial coatings are reflected in the products' prices. On Amazon, a gallon of Rust-Oleum's 7400 System Alkyd Enamel costs $74.49. A gallon of the 9100 System Epoxy Mastic with one gallon of the required activator is $195.74. And the 9800 System Urethane Mastic is $205.02 a gallon; separately, a package with two quarts of activator is $95.74.

Painter said homeowners who want to use Burke's flaked stainless steel coating (which can be used on galvanized or bare steel, or scuffed-up painted steel) generally buy directly from the manufacturer by emailing orders to burkeindustrialcoatings.com. The stainless steel epoxy, Corro Guard 316, is $180.30 a gallon for Part A; the Part B catalyst, to be added in a 2:1 ratio, is $54.43 a quart or $204.12 a gallon. Corro Guard Primer is $141.75 a gallon; it needs the catalyst in a 4:1 ratio.

Besides trying a different coating, removing all the rust you can and using a recommended primer, there is one other thing you can do to keep your steps looking good: Keep the surfaces dry. Sweep away leaves regularly and consider trimming back shrubs or trees that may be keeping the steps shaded. "The area needs access to sun, air movement and frequent removal of plant debris to allow moisture to dry," Wilgen said.

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