Our criteria:1st-grade-this includes lumber with a minimum number of knots, cracks. On the boards there are no rotten damage, through holes, traces of parasites, as well as mold and other foreign elements.2nd-grade-this category includes lumber with small "defects" that do not spoil the appearance of the product. It is not allowed to have deep cracks, rotten knots, rottenness. Acceptable defects include the presence of loose knots with a diameter of up to 20 mm.Grade 3 is a group of low-quality lumber. The main requirement is the absence of large fused knots and deep cracks. Traces of wormholes, through cracks, tobacco knots and mold are quite acceptable. In addition, this type has a fairly low load-bearing capacity.Grade 4 is the cheapest class of lumber, which involves a large number of flaws. Permissible defects: roughness, krylovatost total damage rot, intergrown knots, presence of wane.