The fire resistance of wood-based panels is, in addition to the mechanical and sorption properties, an important property when considering their usability for construction. Increased fire resistance is achieved through the addition of fire retardant during panel production or by spraying fire retardant on already finished panels. With the aim of determining the impacts of the addition of a fire retardant (Burnblock) on the mechanical, sorption and fire resistance properties, we produced three-layer particleboard to which we added various amounts of Burnblock. An appropriate amount of Burnblock (between 10 kg/m³ and 30 kg/m³, depending on the weight of the wood) was added during the preparation phase of the adhesive mixture, or an aqueous solution (18.5%) was sprayed on the outer layer, before compressing. Humidity, density and thickness, thickness swelling and water absorption, bending strength and modulus of elasticity, internal bond, surface soundness and degree of fire retardation were determined for all particleboards. We were discovered that the addition of Burnblock reduces the thickness swelling (positive effect) as well as the bending strength and modulus of elasticity (negative effects). The rate of change with an increasing amount of Burnblock decreases because the addition of fire retardant to the surface layer has a minimal effect on the internal bond. Looking at the results at 60 seconds exposure, the addition of Burnblock had no effect on fire resistance, since the mass loss rate was higher, while at longer exposures (300 seconds) the weight loss trend is reversed. With a longer exposure time, we observed that as the Burnblock content increased, while the thickness of the charred layer decreased.
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