Module 3 of 4

Treat, Prime & Fill

[VISUAL PLACEHOLDER] Module 3 banner: spraying primer-surfacer; self-etch on bare metal; glaze over a low spot.

TREAT, PRIME & FILL (The 30-second Lesson Overview)

Treat the substrateBare steel/aluminum/galvanized get self-etch or a conversion coating; plastics get adhesion promoter; composites usually do not need self-etch.
Primer-surfacerA high-build 2K urethane undercoat that fills sand scratches and small imperfections, then gets block sanded.
Finishing filler (glaze)A thin putty for minor pinholes and low spots after primer, sanded smooth.
Primer-sealerSeals the surface, blocks solvent penetration, gives a uniform ground color, and improves adhesion. It does not fill deep scratches.
Find pinholesA guide coat and block sanding reveal pinholes and lows after primer.
Goal: choose the right treatment for the substrate, apply and sand primer-surfacer, fill minor imperfections, seal correctly, and catch pinholes before paint.
๐Ÿ’ก Did you know? Self-etching primer contains a mild acid (usually phosphoric) that micro-etches bare metal so the paint can grip. It is chemistry doing part of the sanding for you, which is why it goes straight on clean bare metal.
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Safety first

The skills

[VISUAL PLACEHOLDER] Substrate chart: steel, aluminum, galvanized, plastic, composite, with correct treatment.

Identify the substrate & apply the right treatment

ASE Surface Prep Task ยท A10"Apply a suitable metal treatment, conversion coating, or self-etching primer according to product directions."What it means: treat each bare substrate so the coating bites in and corrosion is stopped before primer.
Why it matters: Each substrate (steel, aluminum, galvanized, plastic, composite) needs a specific treatment to bite and resist corrosion. The wrong one peels or rusts.
How it's done: Confirm the substrate, then apply the matching treatment: self-etch or conversion coating on bare steel, aluminum, or galvanized, and an adhesion promoter on plastics, per product directions.
What you need: Self-etching primer or conversion coating, an adhesion promoter, the correct product for each substrate, plus a respirator and gloves.
โš  Common Pitfalls
  • Putting self-etch primer where it is not needed (over fillers or composites) or skipping it on bare steel and aluminum where it belongs.
  • Treating self-etch as the final surface instead of following it with primer-surfacer or sealer per the paint system.
  • Mismatching the treatment to the metal (for example a steel product on aluminum or galvanized), causing adhesion or corrosion problems.
  • Letting treated metal sit past the product's recoat window before you coat over it.
Key pointsBare steel, aluminum, and galvanized need a self-etching primer or conversion coating to bite and resist corrosion. Plastics need an adhesion promoter. Carbon fiber and fiberglass composites generally do not need self-etch.
How to Do It (Step by Step)
  1. Identify the bare substrate.
  2. Clean it for that material (plastic cleaner for plastic, etc.).
  3. Apply the correct treatment: self-etch/conversion for bare metals, adhesion promoter for plastics.
  4. Follow with the proper undercoat per the TDS.
๐ŸŽฌ Video demo + narration
Film this procedure (or build a narrated slideshow from the step images). Save as ase_b2a_substrate_demo.mp4 in this category's images folder, then swap this box for a <video> player.
Narration script (read in order):
  1. Identify the bare substrate.
  2. Clean it for that material (plastic cleaner for plastic, etc.).
  3. Apply the correct treatment: self-etch/conversion for bare metals, adhesion promoter for plastics.
  4. Follow with the proper undercoat per the TDS.
๐Ÿ“ท Step-by-step image prompts โ€” consistent series (generate in one session; reuse the same subject/style reference so every step matches)
Step 1 โ€” save as ase_b2a_substrate_s11.jpg: Create an image showing this exact step in an automotive refinishing lesson: Identify the bare substrate. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 2 โ€” save as ase_b2a_substrate_s21.jpg: Create an image showing this exact step in an automotive refinishing lesson: Clean it for that material (plastic cleaner for plastic, etc.). CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 3 โ€” save as ase_b2a_substrate_s31.jpg: Create an image showing this exact step in an automotive refinishing lesson: Apply the correct treatment: self-etch/conversion for bare metals, adhesion promoter for plastics. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 4 โ€” save as ase_b2a_substrate_s41.jpg: Create an image showing this exact step in an automotive refinishing lesson: Follow with the proper undercoat per the TDS. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.

Remember: Bare metal needs etch; plastic needs adhesion promoter; composite usually needs neither.

๐Ÿ”ง Practice in the Lab: Match the substrate to the treatment

GoalGiven steel, aluminum, plastic, and composite samples, name and apply the correct treatment for each.
Skill checkSelf-etch/conversion for the metals, adhesion promoter for plastic, neither for composite.
[VISUAL PLACEHOLDER] Spraying even coats of 2K primer-surfacer with flash between coats.

Mix & apply primer-surfacer

ASE Surface Prep Task ยท A11"Mix and apply primer, primer-surfacer, or primer-sealer."What it means: mix to the exact ratio and lay down the high-build undercoat that fills sand scratches and is made to be block sanded.
Why it matters: Primer-surfacer fills fine scratches and builds a sandable film so you can level the repair flat before color. Mixed or applied wrong, it will not sand or hold.
How it's done: Mix on-ratio and activate, apply in proper coats with flash time between, then let it fully cure before block sanding.
What you need: Primer-surfacer, activator and reducer, mixing cups and stir sticks, a spray gun, plus an organic-vapor or supplied-air respirator and gloves.
โš  Common Pitfalls
  • Mixing off-ratio or not stirring and activating fully, so it will not sand or cure correctly.
  • Piling on heavy coats with no flash time, trapping solvent (solvent pop, shrinkage, and sand scratches that reappear).
  • Priming a dirty or improperly sanded surface, which causes adhesion failure.
  • Block sanding before it is fully cured, so it gums up and keeps shrinking afterward.
Key pointsHigh-build 2K urethane primer-surfacer fills fine sand scratches and minor imperfections and is meant to be block sanded flat. Apply in proper coats with full flash between them.
How to Do It (Step by Step)
  1. Mix to the exact ratio on the TDS with the correct activator and reducer.
  2. Apply medium, even coats, allowing full flash time between coats so solvent escapes.
  3. Let it cure before sanding so it will not keep shrinking.
  4. Block sand flat with a guide coat.
๐ŸŽฌ Video demo + narration
Film this procedure (or build a narrated slideshow from the step images). Save as ase_b2a_primer_demo.mp4 in this category's images folder, then swap this box for a <video> player.
Narration script (read in order):
  1. Mix to the exact ratio on the TDS with the correct activator and reducer.
  2. Apply medium, even coats, allowing full flash time between coats so solvent escapes.
  3. Let it cure before sanding so it will not keep shrinking.
  4. Block sand flat with a guide coat.
๐Ÿ“ท Step-by-step image prompts โ€” consistent series (generate in one session; reuse the same subject/style reference so every step matches)
Step 1 โ€” save as ase_b2a_primer_s11.jpg: Create an image showing this exact step in an automotive refinishing lesson: Mix to the exact ratio on the TDS with the correct activator and reducer. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 2 โ€” save as ase_b2a_primer_s21.jpg: Create an image showing this exact step in an automotive refinishing lesson: Apply medium, even coats, allowing full flash time between coats so solvent escapes. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 3 โ€” save as ase_b2a_primer_s31.jpg: Create an image showing this exact step in an automotive refinishing lesson: Let it cure before sanding so it will not keep shrinking. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 4 โ€” save as ase_b2a_primer_s41.jpg: Create an image showing this exact step in an automotive refinishing lesson: Block sand flat with a guide coat. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.

Remember: Primer-surfacer is made to be sanded. Build it, flash it, cure it, block it.

๐Ÿ”ง Practice in the Lab: Mix and apply primer-surfacer

GoalMix 2K primer-surfacer to the exact ratio, spray even coats with proper flash, let it cure, then block.
Skill checkCorrect mix ratio, even build, full flash between coats, and it block-sands flat with no shrink-back.
[VISUAL PLACEHOLDER] Spreading thin glaze putty over pinholes/low spots on primer.

Apply finishing filler (glaze) to minor imperfections

ASE Surface Prep Task ยท A12"Apply two-component finishing filler (glaze) to minor surface imperfections."What it means: fill the small pinholes and shallow lows that primer alone will not fill, then sand smooth and re-prime.
Why it matters: Glaze (finishing filler) fills the minor pinholes and scratches that body filler and primer leave behind, so they do not show in the gloss.
How it's done: Over a clean, properly prepared surface, press a thin coat of glaze into the imperfections, let it cure, then block it flat.
What you need: Finishing or polyester glaze, spreaders, a sanding block and abrasives, plus gloves and a respirator.
โš  Common Pitfalls
  • Using glaze to fill deep damage it was never meant for instead of correcting it with body filler first.
  • Applying it over a glossy or contaminated surface, so it lifts or will not stick.
  • Not pressing it into pinholes and scratches, which leaves voids that show back up in the finish.
  • Building it too thick or not letting it cure, so it shrinks and maps later.
Key pointsA thin finishing filler or glaze handles small chips, pinholes, and shallow lows that primer alone will not fill. It is sanded smooth, then re-primed.
How to Do It (Step by Step)
  1. Sand and clean the area.
  2. Spread a thin layer of finishing filler over the minor imperfections.
  3. Let it cure, then sand smooth and flat.
  4. Re-prime over the filled area.
๐ŸŽฌ Video demo + narration
Film this procedure (or build a narrated slideshow from the step images). Save as ase_b2a_glaze_demo.mp4 in this category's images folder, then swap this box for a <video> player.
Narration script (read in order):
  1. Sand and clean the area.
  2. Spread a thin layer of finishing filler over the minor imperfections.
  3. Let it cure, then sand smooth and flat.
  4. Re-prime over the filled area.
๐Ÿ“ท Step-by-step image prompts โ€” consistent series (generate in one session; reuse the same subject/style reference so every step matches)
Step 1 โ€” save as ase_b2a_glaze_s11.jpg: Create an image showing this exact step in an automotive refinishing lesson: Sand and clean the area. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 2 โ€” save as ase_b2a_glaze_s21.jpg: Create an image showing this exact step in an automotive refinishing lesson: Spread a thin layer of finishing filler over the minor imperfections. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 3 โ€” save as ase_b2a_glaze_s31.jpg: Create an image showing this exact step in an automotive refinishing lesson: Let it cure, then sand smooth and flat. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 4 โ€” save as ase_b2a_glaze_s41.jpg: Create an image showing this exact step in an automotive refinishing lesson: Re-prime over the filled area. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.

Remember: Glaze is for the small stuff after primer, not for fixing dents.

[VISUAL PLACEHOLDER] Spraying primer-sealer for a uniform ground color before basecoat.

Apply primer-sealer & adhesion promoter

ASE Surface Prep Task ยท A13"Apply a suitable sealer to the surface prior to topcoat application."What it means: seal the surface and set an even ground color so the topcoat hides and bonds, without trying to fill scratches.
Why it matters: Sealer gives a uniform ground color and seals the surface so the topcoat hides evenly and adheres, while adhesion promoter handles slick substrates.
How it's done: Apply sealer over the prepared surface, observe the flash and recoat window, and add adhesion promoter where the substrate needs it before color.
What you need: Primer-sealer, adhesion promoter, and a spray gun, plus an organic-vapor or supplied-air respirator and gloves.
โš  Common Pitfalls
  • Skipping sealer over a patchy substrate, so the color hides unevenly and ring or sand-scratch lines show.
  • Missing the flash and recoat window: topcoating sealer too soon, or after it has gone past its window, hurts adhesion.
  • Forgetting adhesion promoter on slick substrates (some plastics and cured OEM finishes), which leads to peeling.
  • Sealing over uncured primer or leftover contamination.
Key pointsA sealer locks down the surface: it stops topcoat solvents from soaking in, gives a uniform ground color so the color hides evenly, and improves adhesion. It is not a filler and will not bury deep sand scratches.
How to Do It (Step by Step)
  1. Finish-sand and clean the primer.
  2. Choose a sealer ground color that helps the topcoat hide.
  3. Apply per the TDS and respect the recoat window before basecoat.
  4. On hard-to-coat surfaces, use the correct adhesion promoter.
๐ŸŽฌ Video demo + narration
Film this procedure (or build a narrated slideshow from the step images). Save as ase_b2a_sealer_demo.mp4 in this category's images folder, then swap this box for a <video> player.
Narration script (read in order):
  1. Finish-sand and clean the primer.
  2. Choose a sealer ground color that helps the topcoat hide.
  3. Apply per the TDS and respect the recoat window before basecoat.
  4. On hard-to-coat surfaces, use the correct adhesion promoter.
๐Ÿ“ท Step-by-step image prompts โ€” consistent series (generate in one session; reuse the same subject/style reference so every step matches)
Step 1 โ€” save as ase_b2a_sealer_s11.jpg: Create an image showing this exact step in an automotive refinishing lesson: Finish-sand and clean the primer. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 2 โ€” save as ase_b2a_sealer_s21.jpg: Create an image showing this exact step in an automotive refinishing lesson: Choose a sealer ground color that helps the topcoat hide. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 3 โ€” save as ase_b2a_sealer_s31.jpg: Create an image showing this exact step in an automotive refinishing lesson: Apply per the TDS and respect the recoat window before basecoat. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 4 โ€” save as ase_b2a_sealer_s41.jpg: Create an image showing this exact step in an automotive refinishing lesson: On hard-to-coat surfaces, use the correct adhesion promoter. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.

Remember: Sealer seals and evens the ground color; it does not fill. Fix scratches before you seal.

[VISUAL PLACEHOLDER] Guide coat over primer revealing pinholes after a block-sanding pass.

Identify & correct pinholes

ASE Surface Prep Task ยท A14"Apply a guide coat; identify and correct pinholes and minor surface imperfections."What it means: use a guide coat and a block to reveal and fix pinholes and lows before you spray color.
Why it matters: Pinholes are tiny voids that show up as specks in the finish if you coat over them. Finding and filling them first keeps the topcoat clean.
How it's done: Use a guide coat to reveal them, then work glaze or primer down into the holes and re-level, rather than spraying over them.
What you need: A guide coat, glaze or spot putty, and a sanding block with fine abrasive, plus gloves and a respirator.
โš  Common Pitfalls
  • Priming or painting over pinholes instead of finding and filling them first, so they show up in the gloss.
  • Not using a guide coat, so the pinholes go unnoticed until the topcoat reveals them.
  • Glazing over pinholes without actually working the filler down into the holes.
  • Causing new pinholes by applying filler or primer too thick or too fast and trapping air or solvent.
Key pointsAfter priming over filler, a guide coat and a flat block reveal pinholes, low spots, and shrinkage. Find them now, not after you spray color.
How to Do It (Step by Step)
  1. Apply a guide coat over the primer.
  2. Block sand with fine grit; pinholes and lows hold the guide coat.
  3. Fill pinholes with glaze, re-prime, and re-block.
  4. Confirm the surface is flat and pinhole-free before sealing.
๐ŸŽฌ Video demo + narration
Film this procedure (or build a narrated slideshow from the step images). Save as ase_b2a_pinholes_demo.mp4 in this category's images folder, then swap this box for a <video> player.
Narration script (read in order):
  1. Apply a guide coat over the primer.
  2. Block sand with fine grit; pinholes and lows hold the guide coat.
  3. Fill pinholes with glaze, re-prime, and re-block.
  4. Confirm the surface is flat and pinhole-free before sealing.
๐Ÿ“ท Step-by-step image prompts โ€” consistent series (generate in one session; reuse the same subject/style reference so every step matches)
Step 1 โ€” save as ase_b2a_pinholes_s11.jpg: Create an image showing this exact step in an automotive refinishing lesson: Apply a guide coat over the primer. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 2 โ€” save as ase_b2a_pinholes_s21.jpg: Create an image showing this exact step in an automotive refinishing lesson: Block sand with fine grit; pinholes and lows hold the guide coat. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 3 โ€” save as ase_b2a_pinholes_s31.jpg: Create an image showing this exact step in an automotive refinishing lesson: Fill pinholes with glaze, re-prime, and re-block. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.
Step 4 โ€” save as ase_b2a_pinholes_s41.jpg: Create an image showing this exact step in an automotive refinishing lesson: Confirm the surface is flat and pinhole-free before sealing. CONSISTENT SERIES STYLE (keep identical across every step): the SAME refinish technician (same face and build, navy shop uniform), the SAME clean, brightly lit collision-repair booth, the SAME medium working camera distance and soft, even lighting. If a technician or hands appear, show correct PPE for the task. Photorealistic, true-to-life color, no text, no watermark. Aspect ratio 16:9.

Remember: A guide coat and a block find pinholes before the customer does.

๐Ÿ”ง Practice in the Lab: Guide-coat, glaze & find pinholes

GoalApply a guide coat, block sand, then glaze any pinholes/lows and re-prime.
Skill checkGuide coat clears off the highs, lows and pinholes are found and filled, surface is flat before sealing.
Check what you learned

Substrate treatment

Which of these bare materials does NOT require a self-etching primer?

Carbon fiber or fiberglass. Composites do not need self-etch; bare metals do, to bite and resist corrosion.

Primer-sealer

All of the following are valid reasons to use a primer-sealer EXCEPT:

Filling deep sand scratches. Sealer is not a filler. Deep scratches must be sanded out or filled with primer-surfacer before sealing.

Find pinholes

After priming over a body-filler repair, which method is most likely used to find minor low spots, pinholes, and shrinkage?

Block sanding with a guide coat. The guide coat stays in the lows and pinholes as you block, showing exactly where to fill.

# Numbers & Specs for this module

Substrate treatment: bare steel, aluminum, and galvanized need self-etch primer or a conversion coating; plastics need an adhesion promoter; carbon fiber and fiberglass generally need neither.

Primer-surfacer: a high-build 2K urethane undercoat that fills fine sand scratches. Mix to the exact ratio, apply in even coats with full flash time, let it cure, then block sand.

Primer-sealer seals, gives a uniform ground color, and improves adhesion. It does NOT fill deep scratches. Always verify mix ratios, induction/flash times, and recoat windows on the product data sheet.