Hand-Sanding Window Mullion Grids with Thin Stick Abrasives

Window mullion grids—the narrow dividers that separate glass panes—require delicate sanding to maintain crisp edges and consistent paint coverage. Power tools can easily gouge or round the slender profiles. This guide explains how to hand-sand mullion grids effectively using thin stick abrasives and the correct grit sequence for a flawless, factory-level finish.

Why Sanding Matters for Mullions

Mullion grids collect dust, fingerprints, and paint buildup along their edges. Light sanding removes surface imperfections and ensures uniform primer adhesion. Skipping or overdoing this step leads to rough texture, visible brush marks, or uneven sheen after finishing. Precision and patience are key when working around fragile wood or composite mullions.

Recommended Tools

• Wooden paint stirrers or craft sticks for thin abrasive supports.
• Fine-grit sandpaper cut into narrow strips.
• Detail foam sanding pad for curved corners.
• Vacuum with soft brush nozzle.
• Tack cloth for final cleanup.

Ideal Grit Sequence

• 180 grit – Removes surface roughness or old finish traces.
• 220 grit – Smooths edges and prepares for primer.
• 320 grit – Final polish between coats or before topcoat.

Step-by-Step: Sanding Mullion Grids Cleanly

1. Prepare thin sanding sticks. Wrap 180 Grit (25-pack) paper around a paint stirrer or narrow wooden stick. Secure ends with painter’s tape for a tight fit.
2. Sand the faces. Run the sanding stick along each mullion face, keeping it flat and moving with the grain. Avoid pressing too hard—light passes remove finish uniformly.
3. Refine edges. Use 220 Grit (50-pack) strips folded lengthwise to smooth corners and edge transitions. Check under angled light for gloss variation.
4. Final polish. For a flawless pre-paint surface, go over each mullion lightly with 320 Grit (100-pack) wet/dry sheets. This step eliminates fine dust fibers that can appear as specks under finish.
5. Clean carefully. Vacuum all dust and wipe each mullion with a tack cloth. Pay special attention to corners where dust collects near glazing beads.
6. Prime and finish. Apply a thin primer coat using a foam brush or spray for even coverage. Once dry, sand lightly again with 320 grit before final topcoat.

Special Cases

For vinyl or aluminum mullions, use non-abrasive pads instead of sandpaper to avoid scratching. When refinishing painted wood, focus only on dulling the sheen—don’t try to remove all old paint. For historic windows, use ultra-fine abrasives (400 grit) to preserve patina.

Pro Tips

• Cut sandpaper strips no wider than 1 inch to maintain flexibility in tight spaces.
• Always sand toward glass edges, not across them, to avoid chipping paint at the glazing line.
• Replace loaded strips frequently—fine mullion dust clogs quickly.
• Keep the workspace bright and clean—raking light reveals missed gloss spots immediately.
• Use painter’s tape along glazing if refinishing near installed glass.

Aftercare

• Dust windows gently using a microfiber cloth after painting.
• Inspect mullion joints annually for paint cracking or separation.
• Touch up edges promptly to prevent moisture from wicking under paint.
• Maintain controlled humidity indoors to reduce wood expansion and paint stress.

FAQs

• Can I sand mullions with an orbital sander? No—the small profiles require manual control only.
• What if paint overlaps onto glass? Wait until dry, then scrape gently with a razor blade at a shallow angle.
• Do I need to prime again after sanding? Yes, if you expose bare wood or remove sheen completely.

Watch & Learn

With the right grit sequence from 180 to 320 and custom thin stick abrasives, you can restore window mullion grids to a smooth, professional finish. The result—crisp lines, clean reflections, and lasting beauty for your interior or exterior windows.