Sanding Powder-Coated Parts for Repaint: Adhesion Checklist

Powder coat is tough, slick, and great at resisting weather—until you need to repaint it. Whether you’re refreshing faded railings, color-matching a machine guard, or fixing chipped bike racks, the key to lasting results is controlled sanding that creates uniform tooth without gouging into bare metal or polishing the surface too smooth. This guide lays out a practical, step-by-step workflow that cleans, scuffs, and refines powder-coated parts so primers and topcoats bond and lay down level.

Why sanding powder coat matters

Powder coat is a baked-on polymer film that’s harder than many liquid paints and less permeable to solvents. Most coatings struggle to bite into its glossy surface unless you create a shallow, uniform scratch. Too coarse a grit cuts fast but leaves tracks that telegraph through primer; too fine a grit can burnish the film and reduce adhesion. A disciplined 220 → 320 → 400 progression on a hard backer breaks gloss, erases coarse lines, and sets a consistent tooth that high-bond primers love. The result: fewer fisheyes, better chip resistance, and a finer finish under light.

Tools & supplies

• Hard sanding blocks (phenolic/Delrin) sized to your parts; small profile blocks for tubes and edges
• Random-orbital sander with a firm interface pad (optional for flats—blocking keeps things truer)
• Silicon carbide wet/dry sheets: 220, 320, 400 (600 optional between coats)
• Degreaser (wax & grease remover), plastic-safe adhesive remover for labels, isopropyl alcohol (IPA)
• Masking tape and caps to protect threads, bearings, and moving interfaces
• Raking light, marker or layout dye for witness coats
• Shop vacuum, microfiber towels, and a clean, dust-safe work area
• PPE: respirator, gloves, eye protection

Recommended grit sequence

• Initial key (degloss): 220 grit to break the shine and flatten nibs/texture.
• Refine: 320 grit to erase 220 lines and even the field.
• Final bond prep: 400 grit in straight strokes for a tight, shallow scratch.

Step-by-step

1. Deep clean before abrasives. Wash away grime and silicones with your system-approved degreaser. Lift sticker residue with a plastic-safe adhesive remover, then wipe again. A contaminant-free surface prevents smearing and fisheyes when you paint later.
2. Mask what must not be sanded. Tape off threads, bearing seats, machined flats, or any sliding interfaces. Add caps where needed. You want an even scratch only on paintable film.
3. Map the surface with witness marks. Dust a light guide coat (or scribble with a marker). Under raking light, it reveals glossy islands you haven’t touched and helps you avoid low spots from over-sanding one area.
4. Establish the initial key at 220. Back your paper with a hard block and sand with light, overlapping strokes. Your goal is an even matte—no glossy patches. Swap sheets the moment the cut slows so you don’t skate and burnish. For dependable stock at this stage, use 220 Grit Sandpaper (25-pack) and keep fresh pieces ready for corners, tubes, and broad flats.
5. Check edges and profiles. Powder builds thinner at corners and peaks. Keep the block fully supported; do not ‘ride’ an edge. If you must touch a sharp edge, fold a worn 220 piece over a tiny block and kiss it with one or two passes—just enough to dull the sheen.
6. Refine to 320 to erase 220 tracks. Change direction slightly (e.g., from lengthwise to diagonal) so remaining 220 scratches stand out. Stay flat, pressure light. For multi-part batches (racks, rails, machine guards), minimize downtime with 320 Grit Sandpaper (50-pack) so every station has a fresh, fast-cutting sheet.
7. Set final tooth at 400. Make one uniform pass with 400 in straight, overlapping strokes. This tight, shallow scratch profile hides quickly under primer without polishing the film. When you’re prepping a full run of parts and want absolute consistency, finish with 400 Grit Sandpaper (100-pack) so the last piece sands like the first.
8. De-dust and solvent-wipe. Vacuum, tack, and do a light system-approved wipe (avoid flooding seams on assemblies). If your primer specifies a particular cleaner, use it now.
9. Prime within the window. Apply a bonding or epoxy primer rated for slick substrates. Favor two thinner coats over one heavy pass; heavy films can skin and trap solvents. Observe flash times precisely.
10. Optional between-coat tune (600). After primer flashes hard, denib with 600 to knock back dust and refine the scratch. Wipe clean before your color or topcoat.

Special cases

Chalking/faded powder coat: If your rag wipes off pigment, keep cleaning until chalk stops transferring, then sand 220 → 320 → 400. Chalking reduces adhesion if left under new film.

Local chips to bare metal: Feather the chip edges 220 → 320, spot-etch or epoxy prime the metal per your system, then re-enter at 400 across the whole part so texture matches.

Orange-peel or heavy texture in the old powder: You’re not trying to fully level; just reduce peaks enough for a uniform scratch. If you must flatten more, do it with a hard block at 220, then 320 → 400. Do not ‘dig’ lows with fingertip pressure—widen passes so you keep planes true.

Aluminum vs steel parts: Same grits; just watch heat on thin aluminum extrusions. Keep pressure light, swap sheets early, and avoid aggressive solvent puddles on seams.

Complex tubes and curves: Use small, curved hard backers (or a thin cork under a hard block) to keep pressure distributed. Finish strokes should follow the final grain direction (usually along the part’s length).

Plastic caps or inserts left in place: Don’t sand textured plastics. Mask them or pull them—abrasives will polish and create shiny patches.

Pro tips

• Always use hard backing for the cutting grits. Fingers create troughs, rounded edges, and uneven tooth.
• Stick to one direction per grit (e.g., straight at 220, diagonal at 320, straight again at 400). It makes leftover scratches easy to see and remove.
• Replace paper early. A loaded sheet skates and burnishes the film instead of cutting.
• Keep the surface damp, not flooded if you wet-sand. Puddles hide lows and float the sheet; a light soapy mist is enough.
• Log your recipe: primer brand, flash times, and grit stops. Repeating results is easier than reinventing them.

Aftercare

• Allow full cure per the product sheet before heavy use or harsh cleaners.
• Wash with mild soap; avoid silicone-heavy dressings that can make future repaints harder.
• If you scuff a part later, a quick 400 pass and a light recoat usually blends invisibly—don’t sand finer than the primer/topcoat requires.
• Inspect wear areas (handles, foot rails) and touch up early; small chips are easier to feather and reseal.

FAQs

• Can I paint powder coat without sanding? Not if you want durability. A uniform 320–400 scratch dramatically improves adhesion compared with scuff pads alone.
• Is 600 safer? Finer grits reduce visible lines but can polish the film and hurt adhesion. Reserve 600 for light denibbing between coats; finish your prep at 400.
• Should I chemically strip the powder instead? Only if the film is failing, severely textured, or you need bare metal repairs. Stripping adds time and risk; a clean 220 → 320 → 400 scuff works for most intact films.
• Block or DA? Block for control on flats and edges; DA with a firm pad can speed up the 320/400 refinement on broad panels. Always finish with straight, hand-guided strokes.
• Why do I get fisheyes in topcoat? Usually contamination (silicone/oil). Clean twice—before and after sanding—and use system-approved cleaners. Don’t ‘fix’ fisheyes with heavy coats.

Video

Closing

Repainting powder-coated parts isn’t about brute force—it’s about consistent tooth and clean technique. Degrease thoroughly, break gloss at 220, refine at 320, and set final scratch at 400 on a hard backer. Prime within the window, keep coats light with proper flash, and you’ll get a finish that bonds, levels, and lasts—no peeling, no premature chips.