Why ThermoWood® Knotty Pine Finishes at 19mm - And Why That’s the Correct Specification

At QTD, our default approach has always been to machine ThermoWood® Knotty Pine to a 20mm finished thickness wherever the material allows. This remains our preferred outcome, and in stable supply conditions it has historically been achievable.

However, as ThermoWood® production has scaled across Europe, raw material variability, particularly in knotty pine, has increased. In response, the wider market has gradually converged to a 19mm finished thickness as the most reliable and repeatable specification for this specific product.

Following the same engineering logic applied by established producers such as Lunawood, we are now aligning our finished thickness accordingly.

This is not a reduction in quality or material input. It is a refinement of specification to ensure consistency and long-term performance.

The Starting Point Remains a 25mm Board.

ThermoWood® Knotty Pine continues to be sourced as a nominal 25mm ex-sawn board. That has not changed.

The adjustment in finished thickness reflects the realities of processing thermally modified knotty pine, not a change in the grade, the species, or the amount of timber used at the outset.

Why 19mm Has Become the Industry Standard for Knotty Pine ThermoWood®

Thermal modification fundamentally alters the internal structure of timber. In knotty pine, where grain orientation and density vary significantly across the board, this results in:

• Minor cupping across the face

• Localised thickness variation

• Increased sensitivity during machine planning and profiling

To achieve a uniform, flat, and consistently machined product, sufficient material must be removed to eliminate these variations across the entire batch.

In practice, 19mm is the thickness at which this consistency can be guaranteed without selective machining or excessive waste. This is why most European ThermoWood® suppliers now present knotty pine profiles in this dimension.

Consistency Matters More Than Nominal Thickness

From a cladding design and installation perspective, what matters most is:

• Boards that are flat and parallel

• Repeatable profiles

• Fixings that seat correctly

• Packs that behave the same on site

A nominal 20mm finished thickness that varies from board to board is far less useful than a true 19mm finished thickness delivered consistently.

This adjustment ensures that every board supplied meets the same dimensional expectation.

Performance Is Unchanged

Despite the revised finished thickness, ThermoWood® Knotty Pine continues to offer: 

• Excellent dimensional stability relative to untreated pine

• Proven durability for external cladding applications

• Reliable fixing performance

A Specification Aligned with the Market

This shift reflects a broader trend across the European ThermoWood® sector rather than an isolated change. By aligning our finished thickness with established norms, we ensure:

• Compatibility with industry detailing

• Clear expectations for architects and installers

• Consistent results across varying supply batches

It is a practical, specification-led decision designed to support reliable project outcomes.

In Summary

• While it is Quality First with QTD, we will always produce a 20mm thickness where possible. Should consistency look like being compromised, then 19mm will become the norm. 

• ThermoWood® Knotty Pine still begins as a 25mm thick board.

• Supply variability has increased across the market.

• A 19mm finished thickness allows consistent machining, not 18mm or less, as this will compromise performance. 

• This aligns with leading European suppliers.

• Performance and durability remain unchanged.

  
  

  Above all, this change reflects our commitment to consistent and correct specification, rather than chasing nominal dimensions at the expense of reliability.

---

Still Unsure?

Get in Contact with us here: Sales@qtdgroup.com