Removing Mill Glaze on New Siding Before Staining

Freshly milled exterior siding often looks perfectly smooth—but hidden on the surface is a nearly invisible barrier called mill glaze. This shiny layer forms during planing and manufacturing when heat and compression burnish the wood fibers and bring resins to the surface. While it may look attractive at first, mill glaze prevents stains and finishes from penetrating properly, leading to blotching, peeling, or premature failure. The solution? Correct sanding with the right grit range.

Why Mill Glaze Matters

Mill glaze is essentially a hardened, resin-rich layer that seals the wood surface. If you apply stain directly onto glazed siding, the finish won’t absorb evenly. Instead of rich, uniform color, you’ll get patchy absorption and early weathering. That’s why pro builders and painters always include a sanding step before finishing new siding.

Signs of Mill Glaze

• A glossy or glassy sheen on fresh siding
• Water droplets beading instead of soaking in
• Uneven stain absorption during test spots

Best Grits for Mill Glaze Removal

• 80 grit — Cuts through heavy glaze and levels the surface.
• 100 grit — A balance of removal power and surface refinement.
• 120 grit — Final pass for stain-ready texture without closing pores.

Step-by-Step: Sanding New Siding

1. Inspect the boards. Check under raking light. Glossy or resin-rich boards are prime candidates for sanding.
2. Start coarse if needed. For heavy glaze, begin with 80 grit (25-pack). Keep pressure even and move with the grain.
3. Refine with 100 grit. If the surface feels rough after 80 grit, smooth it using 100 grit (50-pack). This step ensures an even sanding pattern across all boards.
4. Finish with 120 grit. Before staining, make a final pass with 120 grit (100-pack). This leaves the surface slightly open for stain penetration while removing scratch marks.
5. Dust control. Vacuum or blow off dust. Wipe boards with a damp cloth or tack rag to avoid contaminating the finish.
6. Apply stain. Use a penetrating exterior stain. Brush or spray evenly, and back-brush to force it into the fibers.

Special Cases

Factory-primed siding: Do not sand through primer—just a light 120 grit scuff is enough.
Cedar and redwood: These softwoods clog paper fast. Keep extra sheets on hand and use open-coat abrasives.
Engineered siding: Always follow the manufacturer’s sanding/staining instructions. Some products require minimal prep.

Pro Tips

• Sand in long strokes with the grain—not across it—to avoid visible scratches.
• Test stain absorption on a small section before committing to the whole wall.
• Replace dull paper quickly; glazed layers are tough on abrasives.
• Work in shade to prevent stain from flashing too quickly after sanding.

Aftercare

• Recoat every 2–3 years depending on exposure and stain type.
• Inspect annually for peeling, especially on sunny south-facing walls.
• Clean siding with gentle soap and water before re-staining—avoid harsh pressure washing.

FAQs

• Can I use a pressure washer instead of sanding? No. Pressure washing won’t remove mill glaze; it only cleans the surface dirt.
• Why not stop at 150 or 180 grit? Higher grits close the pores too much, reducing stain penetration. 120 is the sweet spot for siding.
• Do I need to sand all sides of the board? Focus on exposed faces. Hidden backs rarely need sanding unless you’re sealing all sides.

Watch & Learn

Removing mill glaze may feel like extra work, but it pays off with longer-lasting, richer, and more even stain results. With the right grit sequence and proper prep, your siding will stay protected and beautiful for years.