How to Fix Wash Boarding Defects in Corrugated Board

Wash boarding—also called corrugator shadow or flute show-through—occurs when the flute pattern becomes visible on the outer liner surface. This defect affects print quality and product appearance.

What Causes Wash Boarding

1. Excessive Adhesive Application

Too much adhesive creates wet spots that swell the liner unevenly over the flute tips, causing the pattern to show through.

2. Excessive Pressure

Over-pressure at the double backer crushes the board, making flute tips more visible.

3. Moisture Imbalance

When the liner has different moisture content than the medium, it can shrink or expand unevenly.

4. Thin or Low-Quality Liner

Lightweight liners show flute patterns more readily than heavier papers.

5. High Hot Plate Temperature

Excessive heat can cause rapid, uneven drying that accentuates the flute pattern.

Solutions and Adjustments

Adhesive Optimization

Reduce glue application weight

Ensure uniform glue film across the web

Check doctor roll gaps and condition

Use instant-setting adhesive to minimize moisture penetration

Process Adjustments

Reduce double backer pressure

Lower hot plate temperature gradually

Balance moisture between liner and medium

Check and adjust wrap angles

Paper Selection

Use heavier liner basis weights

Choose papers with good opacity

Consider surface-treated liners for critical applications

Quality Verification

Inspect board at multiple points along the web to identify where the defect originates. This helps target corrective actions effectively.