Wood and plastics
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Wood and Plastics. Major Topics. Classification of Wood Hardwood Softwood Growth of Wood Wood Defects Wood (Lumber) Seasoning/Kiln Drying Moisture Content Cutting. Major Topics con’t. Wood (Lumber) Decay/Insects Grading Sizing (Nominal vs. Actual) Joints Fasteners

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Wood and Plastics

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Wood and plastics

Wood and Plastics

Major topics

Major Topics

  • Classification of Wood

    • Hardwood

    • Softwood

  • Growth of Wood

  • Wood Defects

  • Wood (Lumber)

    • Seasoning/Kiln Drying

    • Moisture Content

    • Cutting

Major topics con t

Major Topics con’t

  • Wood (Lumber)

    • Decay/Insects

    • Grading

    • Sizing (Nominal vs. Actual)

    • Joints

    • Fasteners

  • Prefabricated Wood (Glue-laminated)

Major topics con t1

Major Topics con’t

  • Plywood

  • Other Panels

    • Waferboard

    • Composite

    • Particleboard

    • OSB (Oriented Strand Board)

  • Plastics

Classification of wood

Classification of Wood

  • Hardwood – trees which are deciduous (shed broad shaped leaves annually) ex: Birch, Ash, Maple, Oak

    • Uses: flooring, interior paneling, cabinets & furniture

  • Softwood – trees which are evergreen (needle-like leaves) ex: Southern Pine, Fir, Spruce, Redwood

    • 75% of lumber produced is made of softwood

    • Uses: structural framing lumber, sheathing, roofing, and exterior siding

Growth of wood

Growth of Wood

  • Growth is formed from core (pith) in rings. The # of rings and spacing between rings show age and growing conditions of tree.

  • Wood is made of hollow tubular cells running parallel to the long axis of the tree.

Wood defects

Wood Defects

  • Common defects include: knots, stain, pitch pockets, decay, and cracks.

  • These defects will impact the visual “grading” of wood products

Examples of defects

Examples of Defects

Wane – irregular rounding caused by cutting too close to outside of log


Resin Pocket



  • Broad term that applies to all finished or semi-finished wood shaped with parallel longitudinal surfaces

  • Nominal piece sizing includes:

    • Board -- 11/2” or less thick and 2” or more wide

    • Dimension – 2” to 5” thick and >2” wide

    • Timbers -- 5” or more thick and wide

Lumber measured in board feet

Lumber Measured in “Board Feet”


See page 330 Section for explanation on how to calculate board feet

Pop quiz provide answers to the following

Pop Quiz – provide answers to the following:

  • What is the standard unit of measure for lumber?

  • Calculate the board feet in a 2” x 4” stud 8’-0 long

  • Find the board feet in 60 pieces of 2” x 10” joists 14 feet long.

Pop quiz answers

Pop Quiz Answers

1.Board feet

2.(Thickness [in] x Width [in] x Length [in])/144 = Board Feet

(2 x 4 x [8 x 12])/144 = Board feet

(8 x 96)/144 = Board feet

(768)/144 = Board feet

5.3 Board feet (rounded off)


Thickness (in) x Width (ft) x Length (ft) = Board Feet

2 x 4/12 x 8 = Board feet

2 x .333 x 8 = Board feet

5.3 Board Feet (rounded off)

3.Number of pieces x Thickness (in) x Width (ft) x Length (ft) = Board Feet

60 x 2 x 10/12 x 14 = Board feet

60 x 2 x .833333 x 14 = Board feet

1400 = Board feet

Often written as 1.4 MBM [1.4 Thousand Board Measure]

Seasoning kiln drying

Seasoning/Kiln Drying

  • Seasoning- the process of reducing moisture until a suitable level is achieved (causes shrinking in lumber size)

  • May be seasoned in the air (2-6 months for softwood and may take 4 years for some hardwoods) or by using a kiln

  • A chemical (hygroscopic) may be applied to the wood to keep surface moist to reduce shrinkage cracks (checks)

Moisture content

Moisture Content

  • The strength of wood increases as the moisture content (m.c.) decreases

  • M.C. varies depending on the conditions (geographical region & indoor/outdoor) in which the lumber will be used

  • Typically, m.c. does not exceed 19%



  • Plain-sawed (flat sawed) – lumber which is cut in parallel slides [less waste & cheaper; warps & splits]

  • Edge-sawed – lumber which is cut perpendicular to the exterior of the tree

  • Quarter-sawed – lumber in which the log is 1st cut into quarters and then cut on the diagonal [produces the most attractive wood grains]

Decay insects


  • Termites – destroy wood by chewing it (chemical or physical barriers should be used to deter them)

  • Fungi – feed on wood fibers leaving wood weakened with rotting

  • Avoid placing untreated wood directly in contact with concrete

Pressure treated lumber

Pressure-Treated Lumber

  • Must meet all EPA (Environmental Protection Agency) requirements

  • CCA (Chromated Copper Arsenate) was the most widely used until Dec. 2003 –no longer produced because of environmental concerns

  • The current wood preservatives include:

    • ACQ (alkaline copper quat)

    • Copper Azole (CA types A & B)

    • Sodium Borate (SBX)

      **** Main concern with new products are that they increase the deterioration of fasteners drastically more than CCA did – reduce the life expectancy of a structure by a factor of four

Source: CSI March 2004 publication of The Construction Specifier



  • Depends on the appearance ( # of defects) and strength

  • Lumber pieces are marked with a grade stamp

    • Typical stamp includes

      • Grading body (WWP – Western Wood Products

      • Mill identification

      • Grade name (Const – construction)

      • Moisture content

      • Type of wood (D-Fir – Douglas Fir)

        • See Figs. 6.2-20,-21, and -22 – on pages 335-36 for examples of grade marks

Sizing nominal vs actual

Sizing (Nominal vs. Actual)

  • Lumber is referred to by nominal size but the actual size is less (see lumber sizes handout)

    • 2”x4” actually measures 1-1/2” x 3-½”

    • 1” x 8” actually measures ¾” x 7-1/4”





  • Nails, screws, bolts, staples, anchors, and joist hangers are common fasteners

  • Sizes, styles, and finishes (coatings) depend on the intended application

  • Length of nails designated in “pennies” [d]



See page 361 for Figures 6.6-2

and 6.6-3

**** There are a variety of nailing methods used:

Toe nailing, end nailing, face nailing, blind nailing

**** Standard sizes of common wire nails

Prefabricated wood

Prefabricated Wood

  • Because of the limitations of size of sawn wood – the gluing of smaller pieces together will enable structural members of virtually any length, cross-section, and desired curves to be made

  • Glu-lam members are widely used in areas of construction using arches (must comply with ANSI 190.1)

Gluelams laminated timbers see page 405

GlueLams [Laminated Timbers]See page 405

  • Individual laminations are placed so that:

    • Weak spots are separated from each other to avoid concentration of weakness

    • Appearance flaws in wood are hidden within the member

    • End joints between lams are separated from each other to avoid a plane of weakness

    • The strongest wood is placed where stresses are highest

Species of lumber used for gluelam

Species of Lumber Used for GlueLam

  • Douglas Fir

  • Alaska Cedar

  • Spruce-Pine Fir

  • Southern Pine



  • Plywood is a type of glued, laminated wood. Thin wood layers of laminations are arranged with the grains of each layer perpendicular to the adjacent one.

  • Veneers – the actual laminations consisting of face & back, crossbands, and the inner (core) Usually an odd number of veneers (3-5; may be up to 11)

  • Thickness may range from ¼” – 1 ¼”

Advantages of plywood vs sawn lumber

Advantages of Plywood vs. Sawn Lumber

  • Has great transverse strength which aids in strengthening/bracing entire structure when used over studs, joists, and rafters for wood frame construction

  • Less warping and change due to moisture changes

  • Is more easily bent to form curves for concrete forms or curved wood construction

  • Fabricated in large sheets (4’x8’, typical) which covers larger areas more quickly

  • Can be worked closer to the edges without splitting

  • Desired appearance can be obtained by using thin veneers of high quality wood where they are visible

Grades types of plywood

Grades/Types of Plywood

  • 5 basic grades from best to less desirable finished appearance: A, B, C, C plugged, & D [see figs 6.3-5;6 and 6.3-6 on pages 340-2 for grades]

  • 5 species groups (according to stiffness and strength): Group 1 is the strongest/stiffest

  • Types of plywood: interior and exterior

    • Interior- made with glue suitable for indoor use; available in any grade

    • Exterior – made with hot, phenolic resin glue which is unaffected by water & resists weathering; no veneers below C grade used

Apa engineered wood products

APA – Engineered Wood Products

  • APA – American Plywood Association – key organization for plywood information

  • Website link:


Other panels

Other Panels

  • Waferboard

  • Composite

  • Particleboard

  • OSB (Oriented Strand Board)



  • Usually contain synthetic resins. May also contain plasticizers, fillers, and colorants

  • 2 basic classes of plastics; thermoplastics (no chemical change during heating/cooling) & thermosetting plastics (change chemically when heated and solidify while still hot)

  • Plastic products are strong, light in weight, formable, and resistant to corrosion

Wood and plastics






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  • Construction Principles, Materials, and Methods, Seventh Edition. H. Leslie Simmons, John Wiley and Sons, Inc., 2001.

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