Surface Appearance Classification and Defect Acceptance Criteria
Technical Reference: Latvijas Finieris / Riga Ply – Quality Requirements for Raw Plywood
Reference Standards:
- EN 635-2 – Plywood Classification by Surface Appearance – Hardwood.
- EN 635-5 – Measurement of Surface Characteristics and Defects.
- SFS 2413 – Quality Requirements for Appearance of Plywood with Outer Plies of Birch.
- ISO 139 – Recommendations and Conditions Drawn by Work Group II of the Technical Committee (1994), as referenced by the manufacturer.
Inspection Scope: Raw plywood surface appearance, visible defects, veneer quality and finishing condition.
1. PLYWOOD SURFACE QUALITY GRADES
1.1 Grade S
Recommended Application: High-quality staining and lacquering.
General quality requirements:
- Carefully selected face veneers.
- Limited visible natural defects.
- Controlled colour variation.
- Limited repaired defects.
- Suitable for applications requiring a high-quality visible surface.
Maximum total number of defects: 6.
1.2 Grade BB
Recommended Application:
- Transparent and non-transparent thicker overlays and films.
- Veneering.
- Finishing and coating.
- Applications requiring a relatively solid face appearance.
General quality requirements:
- Natural wood characteristics are permitted within the specified limits.
- Selected knots and veneer defects may be repaired.
- Limited colour variation is acceptable.
- Surface repairs must be properly executed.
Maximum total number of defects: 9.
1.3 Grade WG
Recommended Application:
- Reverse side applications.
- Applications where surface appearance is not a major requirement.
- Panels covered with other materials.
General quality requirements:
- Wider acceptance of natural wood characteristics.
- More visible veneer defects may be present.
- Surface appearance is secondary to the intended application.
Maximum total number of defects: Unlimited.
1.4 Grade WGE
Description:
WGE is a WG-grade plywood surface without open defects, with open defects repaired using filler.
Recommended for applications involving non-transparent finishing materials and overlays.
2. DEFECT CLASSIFICATION AND INSPECTION REQUIREMENTS
The following defect categories are included in the manufacturer’s published inspection system.
- Closed splits and checks.
- Coloured streaks.
- Brown coloured streaks, excluding rot.
- Composed face veneers.
- Curly grain.
- Edge defects caused by sanding or trimming.
- Glue penetration.
- Imprints and bumps.
- Inserts and veneer patches.
- Irregularities in wood structure.
- Open joints.
- Open splits and checks.
- Open splits and checks repaired with putty.
- Other knots and holes.
- Overlap.
- Pin knots.
- Surface roughness.
- Sanding through.
- Sound intergrown knots.
- Unsanded areas.
- Unsound adhering knots.
- Wood discolouration.
All visible defects should be identified, measured and evaluated according to the applicable grade requirements.
3. NUMERICAL DEFECT ACCEPTANCE CRITERIA
The following limits are transcribed and reorganized from the published Riga Ply technical table.
3.1 Closed Splits and Checks
For the grades where permitted:
- Maximum individual length: 200 mm.
- Maximum quantity: 2 per meter of panel width.
3.2 Coloured Streaks
- S grade: Slightly permitted.
- BB grade: Brown coloured streaks, excluding rot, may cover up to 30% of the surface area.
3.3 Edge Defects from Sanding or Trimming
- S and BB: Maximum 5 mm from the edge, not along the entire panel length.
- WG: Maximum 5 mm from the edge.
3.4 Glue Penetration
- S: Occasionally permitted.
- BB: Maximum 5% of the surface area.
3.5 Imprints and Bumps
- BB: Slightly permitted, maximum 2 cm² per panel.
- WG: Slightly permitted.
3.6 Inserts and Veneer Patches
- S: Properly inserted, matching plywood colour, maximum 1 per m².
- BB: Maximum 3% of the surface area.
3.7 Open Joints
- BB: Maximum individual width 2 mm and length 200 mm; maximum 1 per meter of panel width; repaired with putty.
- WG: Maximum individual width 3 mm.
3.8 Open Splits and Checks
- WG: Maximum individual width 4 mm; maximum 2 per meter of panel width.
3.9 Open Splits and Checks Repaired with Putty
- S and BB: Maximum individual width 2 mm and length 200 mm; maximum 1 per meter of panel width.
- WG: Maximum individual width 4 mm; maximum 2 per meter of panel width.
3.10 Other Knots and Holes
- BB: Maximum individual diameter 6 mm; cumulative diameter not exceeding 25 mm/m².
- WG: Maximum individual diameter 15 mm; cumulative diameter not exceeding 100 mm/m².
3.11 Surface Roughness
- BB: Slightly permitted, up to 10 cm²/m², when repaired with putty; maximum 3 defects per panel.
3.12 Sanding Through
- BB: Maximum 10 cm²/m².
- WG: Maximum 20 cm²/m².
3.13 Sound Intergrown Knots
- S: Maximum individual diameter 20 mm; cumulative diameter not exceeding 50 mm/m².
- BB: Maximum individual diameter 25 mm; cumulative diameter not exceeding 60 mm/m².
- WG: Maximum individual diameter 65 mm; cumulative diameter not exceeding 600 mm/m².
3.14 Unsanded Areas
- WG: Maximum 5% of the panel surface.
3.15 Unsound Adhering Knots
- WG: Maximum individual diameter 20 mm; cumulative diameter not exceeding 200 mm/m².
3.16 Wood Discolouration
- S: Slightly permitted.
- BB: Maximum 30% of the surface area.
4. TOTAL DEFECT COUNT REQUIREMENTS
| Plywood Grade | Maximum Total Defects |
|---|---|
| S | 6 |
| BB | 9 |
| WG | Unlimited |
The total number of defects should be evaluated according to the manufacturer’s inspection method and applicable defect definitions.
5. PANEL SIZE AND DEFECT MEASUREMENT
For quality assessment, the published Riga Ply requirements specify the following minimum measurement units:
- Surface-area-based assessment: 1 m².
- Panel-width-based assessment: 1 meter.
If a machined panel is smaller than the minimum unit specified in the table, its size is treated as 1 m² or 1 meter of width for the relevant quality assessment.
Defect measurements should be recorded consistently to ensure comparable inspection results.
6. QUALITY INSPECTION PROCEDURE
The following inspection workflow is recommended when applying the above reference criteria:
Step 1 – Visual Inspection
Inspect both plywood faces under suitable lighting conditions.
Step 2 – Defect Identification
Identify knots, patches, cracks, splits, colour variation, glue penetration and other visible defects.
Step 3 – Defect Measurement
Measure defect dimensions, individual quantities and cumulative measurements where applicable.
Step 4 – Grade Assessment
Compare the observed defects against the applicable grade requirements.
Step 5 – Defect Counting
Record the total number of defects according to the agreed counting method.
Step 6 – Inspection Record
Document the inspection result, product grade, panel dimensions and any non-conformities.
7. IMPORTANT QUALITY CONTROL NOTES
- The inspection criteria must be applied according to the specified plywood grade.
- Different surface grades have different permitted defect limits.
- Surface appearance classification does not independently establish bonding strength or structural performance.
- Each plywood panel is a natural wood product, and some variations in appearance are normal.
- The latest applicable manufacturer’s specification should be checked before final product acceptance.
8. REFERENCE AND ATTRIBUTION
This report is an independently prepared text summary based on the publicly available technical information published by:
AS Latvijas Finieris – Riga Ply
Original reference:
https://e-veikals.finieris.lv/en/products/quality-requirements/raw-plywood
The original manufacturer documentation remains the authoritative reference for its own grading conditions.
This report is intended for technical reference and internal quality-control planning. It is not an official document issued, approved or certified by Latvijas Finieris, Riga Ply or any European standards organization.
