Grade S (Select)
Birch timber, planed both sides, kiln dried to 6-8% moisture content
1.The S grades are sorted by the better face, when the better face is classified as S grade and the back or worse face is at least of 1C grade.
The minimum required yield of clear wood cuttings for an S grade board is 83 1/3 - 100%. The minimum permissible dimension of the clear wood cuttings for the better face of S grade is 76 mm x 2135 mm or 102 mm X 1525 mm. For the S grade boards with surface less than 0,28 m2 in area the yield shall be 100% clear.
The minimum required yield for clear wood cutting area of the 1C grade face is 66 2/3% - 83 1/3%. The minimum dimensions of permissible clear wood cuttings for
the worse faces of 1C grade are 76 mm x 915 mm or 102 mm x 610 mm. The boards of 1C grade with surfaces less than 0.19m2 in area must have 100% clear cutting yield at a face. The boards of 1C grade with surfaces 0.19m2 - 0,28 m2 in area must have 75% clear cutting yield at a face.
2. Required proportion by width: the S grade boards of 152 mm width and wider as well as of 127 mm and 102 mm widths are stacked together evenly combined in
packs to be sold out as a mix in 50:50 ratio, as follows: the boards of 152 mm widths and wider shall amount to minimum 50% of the total volume of the goods shipped.
The amount of narrow boards of 102 mm widths combined with 127 mm wide boards shall not exceed 45% of the total pack volume.
Required proportion by lengths for each order: the lengths from 2440 mm to 3960 mm shall amount to minimum 80%, and the lengths from 1830 mm to 2135 mm shall not exceed 20%.
3. Ready made dimensions for the S grade (measured after kiln drying and planing):
152 mm and wider: 24 mm x 152 mm and wider x 1830-3960 mm. Width tolerance -0/+152 mm. The actual width of the board is measured.
127 mm: 24 mm x 127 mm x 1830 mm – 3960 mm. Width tolerance -0/+24 mm. The actual width of the board is measured.
102 mm: 24 mm x 102 mm x 1830 mm – 3960 mm. Width tolerance -0/+24mm. The actual width of the board is measured.
Thickness of a timber after two sides planing (S2S) with hit or miss (H/M): the thickness of planed boards shall be 24 mm. Unplaned areas of a 24 mm board shall have
sufficient thickness to enable further processing in the USA for planing till the next standard thickness of 20.6 mm. Hit or miss shall not exceed 20% of each face surface area.
4. Colour tolerance for the front face of the board: The clear cut front face is not permitted to have false heartwood (reddish or brownish). Colour tolerance for the
back/worse face of the board: It is permissible to have unrestricted amount of false heartwood (reddish or brownish) on the back/worse face of the board. Note: commonly false heartwood amounts to average 25% of the board's worse face.
5. THE FOLLOWING FLAWS ARE INTOLERABLE: splinterings, stains/dark marks of stickers, bluestain, decay, loose heartwood, checks, bark, excessive mineral veins and flecks.
Kiln dried boards shall be sawn and planed.
Any kinked, contorted boards with dimples are not permitted.