Direct-to-metal products are in wide use in the collision repair industry. They help to ensure protection against corrosion and ensure adhesion of the topcoat. There are several types of direct-to-metal products that are useful in the body shop.

Etch Primers (some 2k)

Self-etching primers are used for bare-metal applications where the user is looking for the ultimate in corrosion protection. They are very low in solids with next to zero filling qualities. Some are even semitransparent. They usually should be followed with a primer, and they should not be top-coated directly with paint. Apply this type of product to aid in adhesion and corrosion protection under other undercoats such as 2k (two-component) urethane or epoxy primers.

An example of a fast-drying, two-component etch primer is DuPont's 22860S. This wash primer maintains excellent corrosion resistance and direct-to-metal adhesion for spot, panel and overall repairs. Most self-etch primers are available in lead- and chromate-free versions.

Benefits of an etch primer:

• Very thin, keeps down film build
• Cost-effective
• Fast application
• Non-sanding
• Super high corrosion protection

• Some have a very small re-coat window

2k Urethane Primer

Urethane primer (2k) is the most common primer used in the auto body and restoration markets. These types of products tend to be high-solids and geared to filling in any surface imperfections during the repair process. Special attention should be given to allow time for the product to flash (air dry) between coats to avoid the possibility for the product to shrink when applied too heavily.

DuPont 4001S, 4004S and 4007S 2k Ultra-Productive-Primer-Filler is designed for those professional users seeking a highly productive 2k primer. This spot and panel primer-filler delivers quality topcoat holdout, fast dry, minimum overspray and ease of sanding in a high build 2k urethane primer filler. It is an ideal all-around primer for applying over polyester body filler and for surfacing your work. If used properly, it provides the proper film thickness under top coats and is the perfect substrate for basecoat and single-stage topcoat repairs or restorations.

Benefits of 2k Urethane Primer:

• Easy to apply and sand
• Applies smoothly
• Fills well with minimal shrinkage

Disadvantages:

• Contains Isocyanates - use proper respiratory protection
• Should always use an etch primer under it

Epoxy Primer/Sealers

Epoxy primer/sealers are good corrosion-resistant products designed for direct-to-metal applications. They have a very sticky resin and will provide good adhesion to most substrates. Typically, they are not designed for filling surface imperfections or to be sanded (the sticky resin makes sanding difficult). They are ideal for use as a primer/sealer on bare metal that requires no surfacing. An example of an epoxy primer is DuPont's 2510S, 2540S and 2570S, which are two-component, non-isocyanate, non-sanding primers with corrosion resistance and excellent adhesion for direct-to-metal application.

These products are available in lead/chromate-free and chromate for use under body filler, polyester putties, primer surfacers and topcoats. These direct-to-metal epoxy primers can be applied over sanded or blasted steel, well-cleaned aluminum, and galvanized or stainless steel without sanding. They reduce the priming process to a few fast and simple steps: clean, apply one coat of primer/sealer followed by a 20-minute to 30-minute dry, then apply the topcoat.

Over steel and hardened aluminum, the process is: clean, sand, clean, apply one coat of primer/sealer followed by a 20-minute to 30-minute dry, and then apply the topcoat. Some metal sanding and all etching and wash primer steps are eliminated. All of the time-consuming water rinse and dry steps are eliminated. These products are ideal for collision- or restoration-type applications. They are a perfect choice for frames and components, radiator supports and surfaces that are sandblasted. You only need to prime and paint. It can be used as a non-sanding primer/sealer, then paint right over it.

Benefits:

• Good chip resistance (not as hard as a urethane)
• Perfect for a "primer/sealer" over bare metal
• Etch primers can be skipped because of its excellent adhesion and corrosion properties, although for maximum corrosion protection, apply a wash etch under the epoxy
• Provides good base under plastic body fillers (skip the etch if you plan to use plastic filler over epoxy)
• Epoxy has no isocyanates

Disadvantages:

• Poor sanding qualities
• Poor filling

Rafael Ochoa is a product specialist for DuPont Performance Coatings.

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