Long hallway with a row of west-facing windows, walls finished to Level 4, painted with an eggshell.

The finisher is likely correct — this is primarily a paint/lighting issue, not a drywall finishing defect.

Why:

• Level 4 finish is appropriate for eggshell paint, which has moderate sheen.
• Eggshell reflects light unevenly across joints/screws due to slight texture differences, especially under low-angle west sun at 5 PM.
• Joints and screws create subtle ridges; eggshell highlights these as visible stripes when light hits at a grazing angle.

Code/Standard Reference:

• GA-216 (Gypsum Association) specifies Level 4 for eggshell/semi-gloss finishes — so the finish meets standard.
• ASTM D3359 (paint adhesion) and D4214 (paint uniformity) govern paint performance, not drywall.

Solutions:

1. Repaint with flat or matte paint — eliminates sheen-driven visibility.
2. Use a high-quality, non-reflective primer (e.g., Zinsser Cover Stain or BIN) before repainting.
3. Skim-coat joints with lightweight compound and sand smooth (if texture is the issue).
4. Install curtains/blinds to reduce direct sun exposure.

Conclusion: The drywall finish is likely fine. The problem stems from eggshell paint reflecting light unevenly under direct west-facing sun. Recommend switching to a flat finish or addressing lighting.

If the homeowner insists on eggshell, a professional painter should assess paint quality/application. If joints are visibly uneven to the touch, then the finisher may need to rework them.

The finisher is wrong. This is a Level 4 finish failure, not a paint problem.

The Code/Standard:

• GA-214-2022 (Levels of Finish): Level 4 requires "all joints and interior angles shall have tape embedded in joint compound and two separate coats of joint compound applied over all flat joints and one separate coat applied over interior angles... fastener heads and accessories shall be covered with three separate coats of joint compound."
• Critical Lighting Clause (GA-214, Sec 3.2 / ASTM C840): "Critical lighting conditions... will highlight surface variations. Level 4 is not recommended where critical lighting occurs... Level 5 is recommended."

The Physics: West-facing windows at 5 PM create grazing light (near-parallel angle). Eggshell paint has enough sheen to reflect this light. A Level 4 finish inherently has minor ridges at tape joints and screw dimples (compound shrinkage, tool marks). Under grazing light, a 1/64" ridge casts a 1" shadow. That is the "stripe."

Why Paint Isn't the Fix:

• Primer/sealer equalizes suction/porosity (flashing), not topography (ridges).
• Thicker paint or flat sheen reduces glare slightly but cannot hide physical texture.
• "Photographing" the wall with a flashlight at night replicates the defect—proving it's texture, not pigment.

The Fix (Choose One):

1. Skim Coat (Level 5): Roll thin all-purpose mud over entire wall, tight-coat with a 12"+ knife/skimmer. Sand, prime, paint. Only permanent fix for critical lighting on Level 4 substrate.
2. Re-texture: Heavy knockdown or orange peel hides ridges. Matches adjacent rooms?
3. Lighting Change: Add cove lighting/uplighting to wash wall at steep angle, eliminating grazing shadows. Cheaper than re-finishing.

Bottom Line: Finisher bid Level 4; spec/conditions required Level 5. Finisher owns the rework.