FW1035 Lecture 13 Bowyer et al, Chapter 13 Lumber Grades • Grading is typically by: • Strength • 1. Visual Estimation • 2. Measured • Appearance • Specialty product needs
Hardwood Lumber Grading Factory Lumber Lengths from 4 to 16 feet in one foot increments, random widths. Graded according to the size and number of small clear “cuttings” that can be cut from board. Dimension and Component Parts Small board or part machined to a size for a particular application. Finished as specified by customer. May be partially or completely machined to final shape Finished Market Commodity Products E.g. strip flooring, railway ties, stair threads, etc. Typically graded according to relevant trade association rules.
Hardwood Factory Lumber Grading • Hardwood lumber grading scheme is set by the NHLA (National Hardwood Lumber Association). • Factory lumber is typically sold by sawmill to a furniture or cabinet manufacturing plant • Grade is proportional to board size and the amount of clear surface area • a higher grade board is long and wide, with a large percentage of its area being defect-free • the clear lumber can be removed in a few relatively large cuttings
Furniture is typically an assembly of small pieces of wood, hence the grading rules for hardwoods.
Hardwood grades are determined on poorer side of board, except for FIF and Selects. NHLA – National Hardwood Lumber Association FAS – Firsts and Seconds FIF – FAS on one face
Example of Specialty Market Product GradingMaple Flooring Manufacturers Association First Grade – one face practically free of all imperfections; variations in natural color of wood allowed. Second Grade – tight, sound knots (except on edges or ends) and other slight imperfections allowed; must be possible to lay flooring without waste. Third Grade – may contain all visual features common to maple; will not admit voids on edges or ends, or holes over 3/8 inch in diameter; must permit proper laying of floor and provide a serviceable floor. Fourth Grade – may contain all visual features, but must be possible to lay a serviceable floor, with some cutting.
Examples of Maple Flooring Grades First Grade Second Grade Third Grade
Softwoods – Graded in Two Major Categories • Construction • Intended for use as it comes from lumber mill • Strength properties are most important • Two subcategories • Visually graded Lumber • Machine graded lumber • Appearance • Intended for remanufacture • Grade is based on appearance • Also called “shop lumber” • Uses: pencil stock, ladder parts, boxes, mouldings, siding, flooring • Also includes specialty species lumber products – e.g. redwood Softwood lumber in the United States is most commonly graded according to the guidelines of the American Softwood Lumber Standard PS 20-70, established by the U. S. Department of Commerce.
Visually Graded Construction Lumber • Defects are allowed to become larger and more frequent as the grade drops. Commonly considered defects: • Location, size and placement of knots • Slope of grain • manufacturing defects (splits from drying • Wane • Warp • It is assumed that as the defects become larger and more frequent, strength properties drop. • Lengths in 2 foot increments (6 to 18 feet) • Common widths – 2, 3, 4, 6, 8, 10, and 12 inches nominal
National Softwood Construction Lumber Grades “Bending Strength” is percentage of properties of clear (defect-free) wood.
Common Visual Lumber Grades No. 1 - Moderate-sized tight knots. Paints well. Used for siding, cornice, shelving, paneling, some furniture. No. 2 - Knots larger and more numerous. Paints fair. Similar uses as No. 1. No. 3 - Splits and knotholes present. Does not take paint well. Used for crates, pallets, sheathing, subflooring, small furniture parts.
No. 1 No. 2 No. 3
Appearance Softwood Lumber Grades Two primary grades – “Finish” and “Select” - Finish grades are higher than Select grades - Subgrades are usually letters – A, B, C, D To simplify grading at the mill, grades are often combined. - E.g. A and B combined to “B&BTR”
Appearance Lumber “Select” Grades A Select - No knots, splits, or other visible defects. Used for fine furniture, exposed cabinetry, trim, flooring B Select - A few, small defects but nearly perfect. Used for fine furniture, exposed cabinetry, trim, flooring. C Select - Small tight knots. May be nearly perfect on one side. Used for most furniture, shelving, some trim and flooring. D Select - More numerous "pin" knots and other small blemishes. May be used for some furniture, shelving, some trim and flooring.
Moisture Content Marking on Grade Stamp S-GRN – Surfaced in green condition. S-Dry – Surfaced dry. MC is less than 19% after manufacture. MC15/KD15 – MC was less than 15% at time of manufacture. KDHT – Kiln-dried and heat-treated. Dried to <19% MC with core brought to 56° C for 30 minutes. HT kills insects and decay fungi spores. Done to meet global shipping requirements. The stamp only shows the MC of the lumber at time of manufacture. Subsequent history (rain, sitting in mud or puddles) may have raised the MC.
Softwood Grading Certification Agencies RIS – Redwood Inspection Agency. Grades redwood lumber only. NELMA – Northeastern Lumber Manufacturers Association. New England and the Middle Atlantic states. NHPMA – Northern Hardwood and Pine Manufacturers Association. Lake States. SPIB – Southern Pine Inspection Bureau. Grades southern pine lumber only. WCLB – West Coast Lumber Inspection Bureau. Pacific coast states. WWPA – Western Wood Products Association. Thirteen western states. There is a similar set-up in Canada with similar grades.
Example of Softwood Specialty Grading California Redwood Association, “Architectural Grades” Clear All Heart Free of defects one face, reverse face may have slight imperfections. Uses - Siding, paneling, trim, cabinetry, molding, fascia, soffits, millwork. Also fine decks, hot tubs, garden structures, industrial storage and processing tanks. Heart B Heartwood grade containing limited knots and other characteristics not permitted in Clear All Heart and Heart Clear. Uses - Siding, paneling, trim, fascia, molding and other architectural uses. Quality decking, garden shelters and other outdoor uses in contact with the ground.
Clear Same general quality as Clear All Heart except contains sapwood in varying amounts. Uses - Siding, paneling, trim, cabinetry, molding, fascia, soffits. Also quality decking, garden shelters and other above-ground applications. B Grade Grade containing sapwood, limited knots and other characteristics not permitted in Clear. Uses - Siding, paneling, trim, fascia, molding and other architectural uses; quality decking, garden shelters and other above-ground outdoor applications.
Machine Graded Lumber MSR – Machine Stress Rated - Based on measured MOE in bending MEL – Machine Evaluated Lumber - Based on estimated density (using x-rays)
Grade Stamp OLMA – Ontario Lumber Manufacturers Association