COSMOLINE RP-342™ UNDERCOATING FAQs

While RP-342™ has been around since WWII and has literally thousands of applications, VEHICLE UNDERCOATING has become one of its most popular. Simply put, it works really well and protects for a very long time.

RP-342™ easily and reliably withstands:

• road salt,
• road debris,
• chemicals and compounds used on roads,
• extreme temperatures,
• high-velocity undercarriage spray (and pressure washing),
• and more…

What areas of vehicles is RP-342™ typically applied to?

• Undercarriage
• Frame/Chassis
• Bumpers
• Wheel wells
• Door panels

What is the difference between the “Heavy” and the “Black” versions of RP-342™?

RP-342™ “Heavy” and “Black” are both comprised of the same original “Heavy” formula and will provide the same level of protection against rust and corrosion. The only difference is the “Black” version is black and conceals/hides your surface with a really nice-looking black coat.   The “Heavy” version is translucent (see through) and has a slight amber-colored tint to it which is only visible when applied to light or shiny (light-reflecting) surfaces. The “Heavy” version allows you to see and monitor your coated surface. If your surface is dark in color, you will not be able to see the “Heavy” version coating.

What kind of general surface prep is required?

In order to ensure adequate adhesion, RP-342™ should be applied to DRY (not oily or greasy) metal/steel surface. Surfaces should also be as clean as reasonably possible.

How long will RP-342™ protect my undercarriage?

RP-342™ can protect your vehicle for years, depending on driving miles, terrain, etc. That being said, we usually suggest you take a look at your applied RP-342™ after a year and then every 4 months or so thereafter to ensure the integrity of the coating hasn’t been compromised. You should be able to see and feel the coating after application.

What is the difference between the “Heavy” and the “Black” versions of RP-342™?

RP-342™ “Heavy” and “Black” are both comprised of the same original “Heavy” formula and will provide the same level of protection against rust and corrosion. The only difference is the “Black” version is black and conceals/hides your surface with a really nice-looking black coat.   The “Heavy” version is translucent (see through) and has a slight amber-colored tint to it which is only visible when applied to light or shiny (light-reflecting) surfaces. The “Heavy” version allows you to see and monitor your coated surface.

Do you need to apply multiple coats of RP-342™?

No. One generous coat is really all you need. If you choose to apply additional coats to build mil thickness, just make sure the initial coat is completely dry before applying a second coat.

Can RP-342™ be applied to rubber and plastic vehicle components?

RP-342™’s “intended use” is being applied to metals/steels as a rust preventative. While we haven’t seen instances where RP-342™ has compromised or degraded rubber and/or plastic components, there is a possibility such damage could occur. For liability reasons, we’d suggest you try to avoid spraying RP-342™ onto rubber and/or plastic components.   TIP: some customers use a piece of cardboard (cheap and effective) to block overspray from getting on rubber/plastic surfaces during application.

What if my frame/surface has existing rust on it?

If you have serious rust (pitted, flaking, etc.) we'd always recommend you treat those areas (with options like wire brush, rust converter, etc.).  If you have light to moderate surface rust, those areas can be coated over and the rust will not spread.  That being said, it's always ideal to remove any and all rust you are willing and able to remove.

We'd suggest you remove the rust you can and just make sure your surface is dry (not oily or greasy) and as clean as reasonably possible to ensure adequate adhesion.  While one generous coat will do the job, if you choose to apply a second, make sure the first coat is fully dry before applying the second coat.

What if I want to use a Rust Converter before applying?

Rust converters can be used if desired as long as the converted surface they leave behind fully cures/dries, which most do. Again, just make sure your “converted” surface is dry before applying RP-342™.

Application and storage temperatures

“Ideal” application temperatures would be in the range of 55-90 degrees F. That being said, RP-342™ can be applied is colder (even freezing) and warmer temps. Cooler temperatures can prolong dry time.

In order to ensure maximum shelf life, it’s recommended cans be stored in temperatures between 55-90 degrees-F and out of direct sunlight.

What other Cosmoline products is RP-342™ compatible with?

All of the following products are compatible with one another:

• RP-342™ “Heavy” (aerosol & bulk)
• RP-342™ “Black” (aerosol & bulk)
• Cosmoline Rust-Veto 342
• Cosmoline Rust-Inhibiting Wax Wraps #714

Can I apply another coating (different product) on top of my RP-342™ coat?

This is not recommended as applying two different products on top of one another can affect both products’ ability to perform as intended.

Does Cosmoline Direct, LLC offer a spray gun and undercoating extension wands? If so, what PSI is recommended during application.

Yes, Cosmoline Direct, LLC does offer a very user-friendly spray gun and two industrial-grade undercoating extension wands. These can be viewed in the “Vehicle Undercoatings” section.

Spray Gun / Compressor Settings: To spray directly out of your spray gun, close the nozzle and set air pressure to 15 psi. When using the mist wand, open the wand 1 turn and allow 35 psi. Adjust as needed.

If you have any questions regarding our bestselling RP-342™ Rust Preventive & Vehicle Undercoating, please contact us and we’d be happy to assist you.