Substrate Selection & Surface Preparation
In technology wood veneer production, substrate preparation is a critical foundation that directly affects bonding strength, surface appearance, and overall product performance. As engineered veneer materials are typically thin (0.10mm–0.50mm), any substrate defects may become visible after lamination if not properly treated.
This article introduces the first stage of the veneering process: substrate selection and surface preparation.
1. Substrate Selection Criteria
Proper substrate selection ensures structural stability and bonding reliability.
1.1 Bonding Strength Requirements
The substrate must meet national bonding strength standards, with a minimum shear strength of 7 MPa.
It must be free from:
Delamination
Blistering
Edge damage
Cracks or severe warping
The board surface should be smooth and even, without contamination, oil stains, glue marks, or deep scratches.
1.2 Moisture Content Control
Substrate moisture content should generally be controlled below 14%.
Excessive moisture may cause localized bubbling during hot pressing, affecting adhesion quality.
1.3 Thickness Tolerance
Thickness deviation should not exceed ±1% to ensure uniform pressing and veneer bonding.
1.4 Defect Management
For substrates with significant color variation, knot clusters, or other surface defects, batch-based classification and treatment are recommended to maintain consistent product appearance.
2. Substrate Sanding
Before veneering, selected substrates undergo surface sanding (single-side sanding) to achieve:
Uniform thickness
Improved surface flatness
Enhanced adhesive bonding performance
Thickness tolerance should be controlled within ±0.10 mm after sanding.
All sanding dust and wood particles must be thoroughly removed prior to the next process step.
3. Substrate Surface Treatment
Technology veneer sheets are manufactured from natural wood or fast-growing species through slicing processes. Due to their thin structure, they cannot effectively conceal substrate defects.
If the substrate surface is not properly treated:
Color differences
Knot patterns
Surface imperfections
may become visible after hot pressing, negatively impacting both product grade and surface aesthetics.
Therefore, substrate surface treatment is an essential step to ensure premium veneer performance.
3.1 Typical Substrate Specification
Example:
1220mm × 2440mm × 3mm poplar plywood, containing natural knot features.
3.2 Veneer Sheet Specification
Example:
Engineered veneer sheet size: 2500mm × 640mm × 0.50mm.
3.3 Wood Filler Application (Base Treatment)
Wood filler (also known as wood putty or base leveling compound) is applied to conceal surface imperfections and enhance bonding performance.
Functions include:
Concealing substrate defects
Improving surface smoothness
Enhancing structural stability
Improving overall finishing quality
Typical mixing ratio:
Yellow component 1 part : White component 2 parts
Approximate cost reference: 5.5 RMB/kg.
3.4 Equipment Configuration
A simplified three-roller coating machine is typically used for base treatment application.
Key configuration includes:
Upper roller: Hard rubber (HB40–50), diameter approx. 210mm
Middle roller: Stainless steel (chrome-plated), diameter approx. 120mm
Lower roller: Stainless steel (chrome-plated), diameter approx. 210mm
The machine operates without a threaded embossing roller, ensuring smooth and even coating.
3.5 Operating Procedure
3.5.1 Machine Setup
Start the coating machine and apply the prepared wood filler into the groove between the upper rollers.
Recommended rotation speed: 60–80 r/min.
3.5.2 Coating Control
Apply a thin and uniform layer of filler onto one side of the substrate.
Recommended application rate:
Approximately 30–40 kg per 30–40 m².
For substrates with significant color variation or heavy knot presence, coating volume may be slightly increased.
After coating, boards should be stacked and conditioned for 5–6 days before further processing.
3.5.3 Drying
After coating, allow the boards to air-dry for approximately 10 minutes until the surface is non-sticky.
The substrate can then proceed to the next processing stage.
Next Article Preview
In Part II, we will introduce the following stages of the technology wood veneering process:
- Adhesive formulation and mixing
- Glue spreading
- Veneer laying
- Hot pressing process
- Edge trimming
- Inspection and packaging
Stay tuned for a comprehensive breakdown of the full veneering workflow.
