The Complete Guide to Metal Preparation for Epoxy Primer in Classic Car Restoration

Proper metal preparation before applying epoxy primer is the most crucial step in the entire automotive painting process. Failure to meticulously clean and prepare metal surfaces guarantees paint failure down the road. This comprehensive guide walks you through every step of preparing your classic car body for epoxy primer, ensuring a professional, long-lasting finish.

Pre-Preparation: Final Body Assembly

Install All Components

The following steps describe the process to prepare the body for bodywork and paint after all fabrication, metalwork, and lead solder work is complete.

During the final stages of metalwork and prior to gapping the body panels:

• Install the engine, transmission, and suspension
• Ensure the car sits on its wheels and tires
• Add weight to the interior and trunk to replicate seats and at least a half tank of gas
• Install doors, hood, and engine lid with all seals and weatherstrips
• Test fit all trim, including side moldings

Critical Point: Bolt all body panels in place using all mounting hardware. Installing body panels with all required hardware and seals ensures exact fitment from this point forward, especially during final assembly.

Create Locating Holes

Drill locating holes for hinges using a 1/8″ drill bit after all panel alignment is complete. This simplifies panel realignment during the bodywork phase. These locating holes will be filled or welded closed before spraying the final round of primer.

Complete Panel Gapping

Once the body is a roller, finish the body gaps using lead solder. The panel gapping process typically takes 4 to 5 weeks when using lead solder. When panel gaps are finished, remove the suspension, engine, and trim, then place the body back onto its portable cart.

Metal Preparation for Epoxy Primer: The Critical Steps

Initial Inspection and Disassembly

Inspect the body one last time to ensure all panel fitment is correct before removing the doors, fenders, hood, and engine lid prior to starting the metal cleaning process.

Step 1: Media Blasting (If Required)

Depending on the amount of surface rust or oxidation present, the body may need media blasting before cleaning with metal cleaner.

If using sand or star blast media (~120 grit):

• Thoroughly sand the metal using a Dual Action (DA) sander with 150 or 180 grit paper
• This minimizes the “tooth” or “diamond” profile from media blasting

Warning: If you skip this step and leave the diamond profile from media blasting in the metal, epoxy primer will not adhere long-term

If using plastic or walnut shell media:

• The metal will be too smooth for epoxy adhesion
• Sand with 80 grit paper to create proper surface texture

Step 2: First Metal Cleaning

Use a non-acidic metal cleaner such as Glasurit 360-4 and red Scotch-Brite pads to remove all oxidation from the metal.

Process:

1. Apply metal cleaner with red Scotch-Brite pads
2. Wipe dry with lint-free rags
3. Repeat multiple times until there is no black residue on the drying rags
4. Optional: If more time is needed to clean the remaining panels, BASF 1000 Multi-Metal Prep Wipes (Part #2053662) can be used over cleaned surfaces to allow more time. But, the metal etched surface must be scuff sanded with a red 3M Scotch-Brite pad and re-wipped before spraying primer

NOTE: Always wear nitrile gloves

Critical Oxidation Timeline

Understanding how quickly bare metal oxidizes is essential:

• Bare steel: Begins oxidizing within 15 to 30 minutes after cleaning
• Aluminum: Begins oxidizing within 15 minutes after cleaning
• Galvanized metal: Takes twice as long to clean as steel or aluminum (relevant for later 911s, not early 911s or 356s)

Special Considerations for Mixed Metal Bodies

If you have aluminum panels on a steel-bodied car (such as a 356 Carrera GT):

Never use the same tools on aluminum that were used on steel panels. This includes sanders and other equipment.

Particles of ferrous metal will embed into the aluminum and cause the aluminum to rust. There is no way to recover from this situation if it occurs.

Step 3: Remove Metal Cleaner Residue

Clean the bare metal with Glasurit Wax and Grease Remover #541-5 to remove residue left from the metal cleaner.

Important: Do not use lacquer thinner or acetone when cleaning bare metal. These solvents flash dry, making the metal cold and causing it to sweat. This creates moisture that leads to surface rust.

Step 4: Deep Clean Rust Pits and Welds

Any rust pit or divot in any weld, no matter how tiny, must be thoroughly cleaned so the metal is completely white all the way to the bottom.

Recommended process:

• Use media blasting with fine glass bead media (240 to 320 grit)
• Inspect with a bright light such as Milwaukee’s Color Match Light to verify complete rust removal.

Note for tight corners: Leave the texture from media blasting in tight corners such as door, hood, or engine lid jambs. Sanding tight corners is not as effective as media blasting, and epoxy primer adheres better to the media-blasted texture in these areas.

Step 5: Final Metal Cleaning Before Priming

Clean the metal again with Glasurit 360-4 metal cleaner:

1. Spray metal cleaner onto the surface
2. Wipe dry with lint-free paper towels or microfiber towels
3. Continue cleaning multiple times until there is no residue on the towels

At this point, the body is ready to mask but not yet ready to prime.

The Priming Process

Step 6: Masking and Booth Preparation

Mask the body to protect:

• Interior surfaces
• Door jambs
• Body openings
• Wheel wells
• Floor pan

Clean the spray booth thoroughly, then push the body into the booth.

Step 7: Section-by-Section Priming Strategy

Key principle: The body must be primed in sections. Even though the metal looks clean, it begins oxidizing within 15 to 30 minutes and must be cleaned within this time limit before spraying epoxy.

Process:

1. Choose which end of the body to prime first
2. Cover the other end to protect it from overspray
3. Prime doors, hood, engine lid, and bumpers separately

Step 8: Final Cleaning Before Epoxy Application

You will need two helpers for this time-critical process:

1. Clean panels with Glasurit 360-4 metal cleaner
2. Follow with Glasurit 541-5 wax and grease remover
3. Repeat several times until no residue appears on drying towels
4. Wipe down with 541-5 wax and grease remover
5. Dry thoroughly with lint-free towels
6. Blow off panels with compressed air to remove residual cleaner
7. Wipe bare metal with BASF 1000 Multi-Metal Prep Wipes (an acid etch that promotes optimal adhesion of EP 569 epoxy to bare metal)

Critical: While the metal is being cleaned, mix enough epoxy primer in RTS (ready-to-spray) mixing and spraying cups so you can switch to the next container and continue spraying without losing time. Time is of the essence!

Step 9: Epoxy Primer Application

Spray two coats of Glasurit (RM) EP 569 epoxy primer (light grey):

1. First coat: Apply a medium wet coat
2. Flash time: Allow approximately 15 minutes between coats
3. Second coat: Apply a second medium wet coat

If spraying the back half on the same day:

• Bake the epoxy for 30 to 45 minutes
• Let the body cool
• Unmask the back half of the body
• Cover the just-sprayed panels to protect from overspray
• Have helpers clean the bare metal while you mix enough epoxy primer
• Spray two coats on the back half

Alternative approach:

• Let the body sit in the booth with exhaust fans running to evacuate overspray
• Allow epoxy to dry until tack-free
• Bake the body the next day

Step 10: Continue Section-by-Section

Repeat the cleaning and priming process until all bare metal sections have been covered with epoxy primer.

Timeline expectations:

• 2 weeks with 2 to 3 technicians working simultaneously
• 4 to 6 weeks total time to clean and prime an entire body is common

This is very time-consuming but absolutely critical

Remember: Hundreds to thousands of labor hours depend on bare metal preparation being done flawlessly.

Curing and Post-Priming Steps

Step 11: Proper Curing Time

Let the epoxy cure for at least 4 days, preferably 7 days.

Summer tip: Push the body outside and let it sit in direct sunlight. Bake the epoxy as much as possible. The drier the epoxy, the better the results.

Once the body and removable panels have been primed and cured for about 1 week, you’re ready to start the bodywork and priming process with vinyl ester primer or acrylic urethane primer.

Step 12: Reassembly Before Bodywork

Before starting bodywork with plastic filler:

• Reassemble the body
• Adjust and align all body panels using all hardware and body seals

Professional tip: Have two sets of seals purchased at the same time to minimize the possibility of panel misalignment due to mismatched seals during final assembly.

Step 13: Sanding Epoxy for Mechanical Adhesion

Sand the epoxy to provide mechanical adhesion for plastic filler or acrylic urethane primer.

Best practice: Prepare one panel at a time to prevent any breakthroughs and ensure the rest of the body remains completely sealed.

Since plastic body filler relies on sanding scratches or a rougher profile to adhere to epoxy, thoroughly prep all rust pits or welds in the same manner as when they were in bare metal.

Technique for pits and welds:

• Use a handheld spot blaster
• Blast spots very lightly with glass bead media
• Work quickly to provide adhesion without breaking through to bare metal

Step 14: Block Sanding and Filler Application

Block sand the epoxy primer on each panel with 180 grit paper to highlight all low spots, then apply plastic filler as needed.

Recommended fillers:

• Evercoat Rage Ultra Extra
• 3M Platinum Select

Application tips:

• Use metal spreaders for flat areas
• Use plastic spreaders for curved panels

Mixing ratio: Always mix plastic filler on a scale at a 2% ratio of catalyst to plastic filler. On hot summer days, this ratio may be slightly reduced, but always refer to the manufacturer’s technical data sheets.

Warning: Never mix filler on cardboard or untreated paper. Some catalyst will be absorbed by the cardboard, compromising the curing ratio and potentially compromising the longevity of the plastic filler.

Final Thoughts

You only get one first impression, and the paint and bodywork are the first things people see on your restored classic car. Taking the time to properly prepare metal surfaces for epoxy primer is not just recommended, it’s essential for a professional, long-lasting finish.

By following these detailed steps and respecting the critical timing windows, you’ll create a foundation that protects your investment of hundreds of labor hours.

Quick Reference Checklist

Before Metal Prep:

• Complete all panel gapping with lead solder
• Install all components and seals
• Create hinge locating holes
• Final fitment inspection

Metal Preparation:

• Media blast if needed (sand to 150-180 grit after)
• Clean with a non-acidic metal cleaner multiple times
• Remove cleaner residue with wax and grease remover
• Deep clean all rust pits and welds
• Final cleaning before priming

Priming:

• Mask body and clean booth
• Work in sections due to 15-30 minute oxidation window
• Final wipe with acid etch prep wipes
• Apply 2 coats of epoxy primer with 15-minute flash time
• Cure for 4-7 days minimum

Post-Priming:

• Reassemble with all hardware and seals
• Sand epoxy with 180 grit for mechanical adhesion
• Apply plastic filler mixed at 2% catalyst ratio
• Block sand and continue bodywork process

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