Polish Cast Aluminum to a Mirror Finish (400–3000 Grit Wet Sand & Buff Guide)

Cast aluminum parts—valve covers, intake manifolds, brackets—can shine like chrome without plating. The key is a tight wet-sanding sequence that erases casting texture, followed by a clean, heat-safe polish. This guide shows the exact grits, pressure, and technique to get a true mirror.

Before You Start

• Degrease completely and remove heavy oxidation with a non-scratching scrub pad.
• Use a soft foam interface pad on curves to avoid flat spots and waves.
• Wet sand only: water with a drop of dish soap (or a light mineral oil/WD alternative) to keep swarf from scratching.

Grit Progression (Wet Only)

• 400 grit — flatten casting texture and file marks; stop when the surface is uniformly matte.
• 600 grit — remove 400 lines; change direction to track progress.
• 800 grit — refine to a tighter haze; edges last to avoid rounding.
• 1000 grit — pre-polish finish; remaining scratches should be very fine under raking light.
• 1500–2000 grit — eliminate micro-marring and shorten buffing time.
• 3000 grit — optional glazing step for a near-gloss before compound.

Step-by-Step

1. Level at 400. Straight, overlapping strokes with light pressure. Keep the surface just wet and wipe slurry often.
2. Refine each stage. With every grit, sand until all previous lines are gone. If you still see 400 scratches at 800, drop back to 600.
3. Edge discipline. Work edges and corners at the end with fresh paper and minimal pressure to prevent rounding.
4. Finish at 2000–3000. Aim for an even, tight haze—no visible lines under a bright work light.
5. Buff. Use a metal polish or aluminum compound on a foam or stitched cotton wheel at low to medium speed. Work small areas and wipe clean between passes.
6. Seal. Optional: apply a polymer sealant or wax to slow down oxidation.

Pro Tips

• Mark the surface with pencil squiggles; when they disappear evenly, you’ve fully hit the surface.
• Replace paper often—dull sheets skate and create random deep scratches.
• Avoid cross-contamination: dedicate one pad per grit and rinse everything between steps.
• For deep casting pits, spot-level with 400 on a small hard block, then blend outward.

Shop the Grits

• Grit 400
• Grit 600
• Grit 800
• Grit 1000
• Grit 1500
• Grit 2000
• Grit 3000
• Shop All Sandpaper

Watch & Learn

Result: A true mirror on cast aluminum with crisp edges—no waves, no leftover casting haze.

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