CLASS I (Selekt) - natura wood graining, unified colouring, no alburnum or other defects. Allowed are knags: sound and accreted ones: max. dia. max. 8 mm; spoiled ones: max. dia. 1 mm. Surface and thunderbolt cracks are not allowed. Considering unavoidable differences in sorting, in each class up to 2 % of lower- quality planks are allowed.
CLASS II (Natur) - mixed graining, with prevalence of flame-grain veins, colouring: more diversified, natural overcolouring spots; allowed are sound and accreted knags: up to 10 mm; spoiled knags: up to 5 mm; alburnum and other defects: unallowed. Surface and thunderbolt crack, up to 15 mm long, are allowed. Sporadical larval holes. Considering unavoidable differences in sorting, allowed are, in each class, up to 2% lower-quality planks.
CLASS III (Rustik) - very diversified graining, vivid ,gay and contrast colouring, natural overcolouring spots. Knags (sound and accreted, and also those spoiled) are allowed without limits of size and quantity, unless they cause strength or wear-resistance reduced. Surface and thunderbolt cracks are allowed. Bio-degradation: unallowed, save for blue- stain defects and black larval galleries.
The bottom layer of the board: all traits are allowed with no limits for size or quantity - unless they cause floor strength or wear-resistance reduced.
Product humidity 9% (+/-2%)