We studied the effects of surface charring on the porosity and liquid water absorption capacity of Norway spruce (Picea abies) wood, which are important properties for easier assessment of the durability and usability of wood after exposure to fire, which is especially important in construction and restoration work. Pieces of wood of 30 mm thickness were charred in a cone calorimeter according to the ISO 5660-1:2015 standard, with a heat flux of 50 kW/m2. Samples with the dimensions 15 × 15 × 30 mm were sawn from the charred pieces, with which we gradually removed the charred material in layers to study the properties according to the degree of charring of the wood. We measured water absorption in wood with five types of surfaces: control wood (1), minimally charred wood (2), charred wood (3), the base of the charred layer (4), and the charred layer (5). The average water uptake was highest in samples with a completely charred layer (5; 287.6 g/m2) and lowest in the charred wood layer (3; 125.6 g/m2). We measured the density and indirectly calculated the porosity of the material removed during sample preparation. The density decreased with increasing thermal degradation. The control spruce had a density of 423.82 kg/m3, while the charred layer had a density of 123.08 kg/m3. In contrast, the porosity increased with the degree of charring, amounting to 91.8% for the charred layer and 71.7% for the control wood. The degree of porosity thus increased with the degree of charring, but the water uptake varied depending on the degree of charring of the wood.
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