Remove Mill Glaze on Siding: 80–120 Grit for Stain Prep

Freshly milled siding often looks smooth and shiny—but that sheen is mill glaze, a heat-burnished layer that blocks stain absorption. If you apply finish over it, the result is patchy color and premature peeling. The solution is a short sanding ladder: 80 ? 120 grit. This breaks through the glaze, opens the pores, and ensures stain penetrates evenly. Here’s how to spot mill glaze and sand it off the right way.

Why Mill Glaze Matters

During planing, heat and compression harden the surface and bring resins up, creating a sealed, glossy layer. Stain can’t soak in, so it beads or wipes off. That leads to uneven tones and poor adhesion. Sanding with 80 ? 120 cuts through without over-polishing, leaving siding ready to take finish deep into the fibers.

Tools & Materials

• Random-orbit sander with firm pad
• 9×11 in sandpaper sheets: 80 and 120 grit
• Hand sanding block for narrow edges
• Pencil for guide-coat, raking light
• Vacuum, tack cloths
• Exterior penetrating stain or sealer
• PPE: respirator, eye and ear protection

Recommended Grit Sequence

• 80 grit — Cuts through glaze, removes planer sheen.
• 120 grit — Refines surface, leaves pores open for stain.

Step-by-Step: Prep New Siding

1. Inspect under light. Look for shiny streaks and resinous patches. Drip water—if it beads, glaze is present.
2. Break glaze with 80 grit. Use 80 grit (25-pack) sheets on a firm pad. Sand evenly with the grain until the gloss is gone.
3. Refine at 120 grit. Switch to 120 grit (50-pack). Sand lightly to smooth the surface without closing pores.
4. Dust control. Vacuum and wipe with tack cloth. Dust left behind blocks stain just like glaze.
5. Stain promptly. Apply penetrating stain the same day. Back-brush to force it in for rich, even color.

Special Cases

Cedar & redwood: Sand lightly—over-sanding burnishes earlywood. Stop at 120.
Factory-primed siding: Don’t cut through primer. Just a light 120 scuff if required.
Engineered products: Follow manufacturer’s sanding rules; some forbid aggressive sanding.

Pro Tips

• Mark with pencil to ensure full coverage—glaze is easy to miss.
• Replace paper often—resins load sheets quickly.
• Work in shade—sun can harden resins and flash stain before it penetrates.
• Always sand with the grain to avoid cross-scratches.

Aftercare

• Inspect siding annually; re-stain every 2–3 years depending on exposure.
• Clean with mild soap—avoid pressure washers that erode finish.
• Spot-fix weathered boards: sand 120, re-stain, blend in.

FAQs

• Can I pressure wash instead? No—washing doesn’t remove glaze, only dirt.
• Why not sand finer than 120? Higher grits polish and close pores, reducing stain penetration.
• Do all new boards have glaze? Not always, but many do—especially from fast-feed planers.

Video: Mill Glaze Removal

Closing: Don’t trap stain behind mill glaze. A quick 80 ? 120 sanding sequence opens the grain, evens absorption, and ensures long-lasting, rich color on new siding.