Why Not All Fire-Treated Wood Is Created Equal

Fire Performance Starts With the Treatment Process

Wood is naturally variable. Density, grain structure, moisture content and species characteristics can differ from one piece to another. An effective treatment process has to account for those variables while producing a finished product with predictable fire performance.

Pressure impregnation approaches that challenge by treating the wood beyond its surface.

During the process, lumber or plywood is placed inside a treatment cylinder where a combination of vacuum and pressure is used to introduce the fire-retardant solution into the wood. After treatment, the material is dried under controlled conditions. The result is a fire-retardant system incorporated into the wood rather than simply applied to its exterior.

Biewer FRTW uses pressure-impregnated treatment systems designed and evaluated for fire-retardant applications. Biewer FRTW for example, is pressure impregnated and manufactured using a treatment process that meets AWPA T1, and treatment chemistry that complies with the AWPA P50 standard.

That distinction matters because how a product is treated is part of how its performance is established.

Pressure Impregnation vs. Surface Treatment

Not every method of altering wood’s reaction to fire works the same way.

Surface-applied treatments place a coating onto the exterior of the wood. Pressure impregnation instead uses a controlled treatment cycle to move the fire-retardant solution into the wood structure. In a typical pressure process, a vacuum removes air before treatment solution enters the cylinder; pressure then drives that solution into the wood before excess treatment is removed and the material is dried.

The difference is more than manufacturing terminology.

A surface application depends heavily on what happens at the exterior of the material. Pressure impregnation creates a treated wood product whose fire-retardant chemistry has been introduced below the surface.

For specifiers and contractors, understanding that distinction is important when evaluating products for a particular application. A similar description—or immediate availability—does not necessarily mean two products were manufactured, evaluated or documented in the same way.

Consistency Requires More Than Chemistry

The treatment chemical is only one part of producing dependable FRTW.

The process surrounding it matters, too.

Variables such as wood species, moisture, treatment formulation, treatment cycle and drying conditions have to be managed so that the finished product corresponds with the performance represented by its testing and documentation.

That is where quality control becomes especially important.

Fire performance is commonly evaluated using ASTM E84 or UL 723 testing, which measures surface-burning characteristics including flame spread and smoke development. But a successful test result is not the end of the manufacturing story. Ongoing production has to consistently represent the product that was originally evaluated.

Quality-control programs provide that connection between tested performance and everyday production. Depending on the applicable product and evaluation pathway, controls can address factors such as treatment formulation, application and retention, recordkeeping, periodic testing and third-party inspection.

In other words, consistency doesn’t happen because a product carries the FRTW designation. It comes from controlling the variables that determine how that product is manufactured.

Why Availability Shouldn’t Be the Only Question

Construction schedules move quickly, and material availability matters. When a substitution is needed or multiple FRTW products are available, however, treating them as automatically interchangeable can overlook meaningful differences.

The question isn’t simply, Can we get fire-treated wood?

It’s whether the available product matches the requirements of the application and is supported by the appropriate treatment process, testing, labeling and documentation.

ICC-ES evaluation reports, for example, provide information about the requirements or acceptance criteria under which a product was evaluated, its installation requirements and how the product can be identified. Product labeling can provide another layer of traceability, identifying information such as the treating manufacturer, treatment, wood species, flame-spread and smoke-developed indices and drying method.

Those details help project teams look beyond availability and understand what they are actually specifying and installing.

Manufacturing FRTW With the End Result in Mind

For Biewer, pressure impregnation is part of a larger approach to FRTW manufacturing built around process control and consistency.

With more than 40 years of experience producing fire-retardant-treated wood, Biewer manufactures pressure-impregnated FRTW for residential and commercial applications. That experience reinforces a fundamental principle: dependable performance begins long before treated material reaches the jobsite.

It begins with the wood, continues through treatment and drying, and depends on maintaining controls throughout production.

That is why FRTW should be evaluated as more than a category of material. The treatment method, manufacturing process, quality controls and supporting documentation all contribute to understanding what is behind the product.

When fire performance is part of the specification, those details matter.

Not all fire-treated wood is created equal—and knowing how it was treated is a good place to start.