How is Plywood made : The Full Process Explained | Part-3

In this article of the series, we will explore the key manufacturing steps that give plywood its strength and rigidity. These include:

• Glue Spreading
• Veneer Assembly
• Cold Pressing
• Hot Pressing

Glue Spreading

After the veneers are clipped, dried, and composed into uniform sheets, they move to the Glue Spreading stage. The strength, durability, and bonding quality of the final plywood depend heavily on how evenly and accurately the glue is applied.

Plywood is made by stacking multiple veneer layers with alternating grain directions. To ensure these layers bond firmly into a single solid panel, the core or panel veneers must be coated with a uniform layer of adhesive. This adhesive penetrates the wood fibers and creates a strong bond during pressing.

The machine used for this is called Glue Spreader Machine, in which glue is applied through a spreader rollers, and excess glue is removed by the doctor (steel) rollers.

Which Veneer gets glued?

For stacking the veneers, glue is applied only on both sides of the core veneers, while the panel (cross-band) veneer placed next to them is kept unglued. This arrangement helps control glue consumption and prevents the panel veneers from over-absorbing adhesive.

After stacking, the entire assembly is hot-pressed, resulting in what is commonly referred to as Mat Ply (explained in detail later). Following a few additional processing steps, this Mat Ply is again sent through the glue spreader, and finally, the face veneer is applied on top and bottom.

Types of Adhesives Used

For gluing, following adhesives are used depending on the grade of plywood.

1. Urea Formaldehyde (UF)
2. Phenol Formaldehyde (PF)
3. Melamine Formaldehyde (MF)
4. Melamine Urea Formaldehyde (MUF)

Veneer Assembly

We have referred to “veneer grains” several times throughout this guide, but we haven’t yet explored what grain actually means or why it plays a crucial role in plywood manufacturing. Understanding veneer grain is essential because it directly influences how veneers are stacked, aligned, and pressed. It ultimately determines the plywood’s strength, stability and durability.

What are veneer grains?

Veneer grain refers to the natural direction of wood fibers in a veneer sheet. When a log is peeled during veneer production, long wood fibers run parallel to the length of the sheet. This alignment of fibers creates what we call the grain direction.

Understanding veneer grains is essential, as the entire structural integrity of plywood is built around managing and orienting these grains correctly.

---

Now, let's come back to the Veneer Assembly part.

Once the veneers have been clipped, dried, conditioned, and composed into standard sizes, the next crucial stage is Veneer Assembly. This step determines the final strength, stability, and quality of the plywood sheet.

Veneer assembly creates a balanced structure by stacking multiple layers of veneers with alternating grain directions. This cross-grained arrangement counters natural wood movement, greatly improving the plywood’s mechanical strength.

These assembled veneer layers are first cold-pressed to lock their position, and then hot-pressed to cure the glue and form a strong, unified plywood structure.

Point to keep in mind during assembly

1. Always use an odd number of veneer layers—such as 3, 5, 7, 9 etc. : This ensures that the plywood has a central core layer and maintains balanced construction, preventing warping. The total number of layers depends on the final thickness required.

2. Maintain a uniform and balanced layup structure: The center layer must always be a core veneer, placed with its grain running in one direction.

   The veneers directly above and below the core must be panel veneers, placed with their grain at 90° to the core grain.

   The next layers (top and bottom) again alternate as core veneers, and this cross-grain pattern continues outward until the face and back veneers are added.

   This alternating grain arrangement is crucial for strength, dimensional stability, and resistance to warping.

3. Glue is applied only to core veneers : Panel veneers and face veneers are generally placed unglued during the initial assembly because they get bonded through the glue-coated core veneers during pressing.

   This prevents over-absorption of glue and ensures uniform bonding.

Cold Pressing

Cold pressing is the process of compressing the glued veneer stack under high pressure but at normal room temperature (no heat applied). The veneers remain in the press for several minutes (e.g. 30-45 minutes), allowing the glue to equally distribute and settle, and the layers to lock in place.

This step is executed -

1. To create the temporary pre bond between the veneers.
2. To remove air gaps and voids
3. To ensure uniform thickness and flatness

The machine used for Cold Pressing is called Hydraulic Cold Press Machine.

Hot Pressing

Hot Pressing is one of the most critical stages in plywood manufacturing, where the stacked and cold-pressed veneers are permanently bonded into a solid, uniform plywood sheet. In this stage, the veneer assembly is subjected to high temperature, controlled hydraulic pressure, and precisely timed pressing cycles.

The adhesive applied on the core veneers requires heat to cure (polymerize). Inside the hot press, temperatures typically range from 120°C to 160°C, depending on the type of glue used. This heat initiates a chemical reaction that converts the adhesive from a liquid or semi-liquid state into a hard, durable resin—ensuring strong and permanent bonding between all veneer layers.

The application of high, consistent pressure ensures complete glue contact, eliminates air gaps, and produces uniform bonding across the entire plywood sheet. It also stabilizes the final thickness and prevents warping.

Depending on the press design, the number of veneers, and the adhesive type, the hot-pressing duration typically ranges from 4 to 12 minutes per cycle.

The output after this stage is generally referred to as Mat Ply, which is then sent for trimming, sanding, and further finishing operations.

Conclusion

In the next article, we will explore the processes that transform the Mat Ply into its usable form—how it is trimmed to standard dimensions and how a perfectly uniform thickness is achieved across the entire surface. We will also dive into the concept of calibration and why it is essential for producing high-quality plywood.