Ford Offers New Corrosion Protection Recommendations - BodyShop Business

Ford Offers New Corrosion Protection Recommendations

From I-CAR

Service information from Ford Motor Company states that corrosion protection needs to be restored whenever it is necessary to sand or grind through painted surfaces or E-coat, or when bare metal repairs are performed. Recently, Ford changed their corrosion protection product recommendations for undercoatings and panel backsides.

New Corrosion Protection Products

Until recently, Ford has been recommending Motorcraft PM-12 and PM-13 to restore corrosion protection to areas such as the backsides of panels, the exterior of frames, and body or frame cavities. PM-12 is a low temperature anti-corrosion coating. PM-13 is a solvent-borne undercarriage/blackout paint.

Now, Ford recommends using Motorcraft Rust Inhibitor PM-24A or -24B to restore corrosion protection to areas such as the backsides of panels, and Motorcraft Premium Undercoating PM-25A or -25B to restore corrosion protection to areas such as the exterior of frames and the backsides of body panels. Products identified with an “A” are supplied in aerosol containers. Products identified with a “B” are supplied in bulk, non-aerosol containers. PM-24 and PM-25 are both Motorcraft part numbers, available from Ford dealerships.

The aerosol products work well for exposed repairs. The non-aerosol products can be applied using spray equipment with a wand attachment. Use a flexible wand or steel tube wand to reach into cavities. Special tools, specifically a rust-inhibitor installation kit and an undercoating spray gun, are available from Ford for application of the non-aerosol form of these corrosion protection products. Comparable spray equipment may also be used.

Rust Inhibitor PM-24 and Undercoating PM-25 are wax-based products and must be thoroughly stirred or shaken before applying to the vehicle. These products should be stored at temperatures above 20°C (68°F) to avoid thickening of the material. If the product has been left in a cold environment, it is recommended to place the container in hot water for 5-10 minutes. Do not let water reach the cap of the container.

PM-25 is applied in locations such as the undercarriage, hidden areas, and wheelhouse areas, as needed. It duplicates the OEM look for frames and underbody use, and can be applied over a light coat of PM-24 if desired. PM-24 is light brown and has a thin consistency when it is at the recommended temperature. PM-25 is black and has a thicker consistency than the PM-24. Neither PM-24 nor PM-25 completely dries to the touch.

Ford no longer recommends using PM-12 anti-corrosion coating. PM-13 is still available but only recommended as an undercarriage paint only, such as for touch-up of trailer hitches, suspension arms, etc.


To avoid personal injury, always refer to Material Safety Data Sheets (MSDS) when handling chemicals and wear protective equipment as directed. Recommended protective equipment for PM-24 and PM-25 includes a vapor respirator, chemically resistant gloves, and face/eye protection.

When restoring corrosion protection using PM-24 or PM-25, metal surfaces must be free of oil, dirt, and other foreign material. Thoroughly clean and degrease metal surfaces with a wax and grease remover. Body panels installed during collision repair that will not be accessible after assembly should be cleaned before installation to improve the adhesion of anti-corrosion materials that are applied when assembly is completed.

Protect adjacent areas of the vehicle from overspray. Avoid applying corrosion protection to mechanical and electrical parts, electric motors, speakers, door locks, and drain holes. Excessive amounts of anti-corrosion materials can plug drain holes and cause water drain problems. Do not allow the material to contact restraint system parts or exhaust system parts.

When using spray equipment, such as the Ford rust inhibitor applicator, to apply PM-24B, the air pressure setting for the applicator gun is 448-517 kPa (65–75 psi). Use a long wand when spraying enclosed areas. Insert the wand as far as possible into the access hole. Depress the trigger, wait 2–3 seconds, and slowly pull the wand out of the access hole. The spray nozzle provides a 360° spray pattern.

When using spray equipment to apply PM-25B, the air pressure setting for the applicator gun is 552-621 kPa (80–90 psi). The non-aerosol container of PM-25B will attach directly to the dispensing gun of the Ford special undercoating spray gun tool. The applicator sprays in a fogging pattern. Depress the trigger, wait 2–3 seconds, and slowly pull the wand to ensure that the area is completely fogged.

For best results, the vehicle should be at room temperature. Apply light mist coats. PM-24 and PM-25 will displace moisture. Do not use high-pressure water spray cleaning on the treated underbody area for 24 hours following application of the corrosion protection product.

Ensure that horizontal surfaces are well protected, as they are more susceptible to corrosion. Clean up any overspray with a mild solvent such as mineral spirits.

Weld-Through Primer

Ford recommends the use of a weld-through primer on bare metal mating surfaces in the immediate area of the weld zone. Most brands of weld-through primer are considered acceptable. Weld-through primer should be used with the proper GMA (MIG) welding or squeeze-type resistance spot welding (STRSW) procedures, for example removing the primer from plug weld holes before welding to avoid weld porosity.

PM-24, PM-25, or PM-13 should not be used as a weld-through primer. They should be applied following the welding process.


Restoring the corrosion protection is an important part of a repair. Ford is now recommending PM-24 and PM-25 for corrosion protection whenever it is necessary to sand or grind through painted surfaces or E-coat, or when bare metal repairs are performed.

For comments or suggestions on the Advantage Online, please contact I-CAR Senior Instructional Designer Bob Jansen at [email protected].

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