Wood and Plastics

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Wood and Plastics
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Major Topics

• Classification of Wood
• Hardwood
• Softwood
• Growth of Wood
• Wood Defects
• Wood (Lumber)
• Seasoning/Kiln Drying
• Moisture Content
• Cutting

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Major Topics cont

• Wood (Lumber)
• Decay/Insects
• Grading
• Sizing (Nominal vs. Actual)
• Joints
• Fasteners
• Prefabricated Wood (Glue-laminated)

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Major Topics cont

• Plywood
• Other Panels
• Waferboard
• Composite
• Particleboard
• OSB (Oriented Strand Board)
• Plastics

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Classification of Wood

• Hardwood trees which are deciduous (shed broad
  shaped leaves annually) ex Birch, Ash, Maple,
  Oak
• Softwood trees which are evergreen (needle-like
  leaves) ex Southern Pine, Fir, Spruce, Redwood

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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.

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Wood Defects

• Common defects include knots, stain, pitch
  pockets, decay, and cracks.
• These defects will impact the visual grading of
  wood products

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Examples of Defects
Wane irregular rounding caused by cutting too
close to outside of log
Knot
Resin Pocket
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Lumber

• 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 gt2 wide
• Timbers -- 5 or more thick and wide

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Lumber Measured in Board Feet
http//www.woodzone.com/tips/board_feet/board_feet
.htm
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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)

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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

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Cutting

• 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

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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

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Pressure-Treated Lumber

• Must meet all EPA (Environmental Protection
  Agency) requirements
• CCA (Chromated Copper Arsenate) is the most
  common treatment used today
• 4- EPA approved wood preservatives include
• Waterborne
• Oil-borne
• Creosote
• Fire-retardant solutions

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Grading

• 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)

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Sizing (Nominal vs. Actual)

• Lumber is referred to by nominal size but the
  actual size is less (see handout)
• 2x4 actually measures 1/1/2 x 3 ½
• 1 x 8 actually measures ¾ x 71/4

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Joints
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Fasteners

• 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

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Nails
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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)

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Glu-Lam

• 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

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Species of Lumber Used for Glu-Lam

• Douglas Fir
• Alaska Cedar
• Spruce-Pine Fir
• Southern Pine

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Plywood

• 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)
  see fig 6-20, pg. 176
• Usually an odd number of veneers (3-5 may be up
  to 11)
• Thickness may range from ¼ 1 ¼

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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 (4x8, 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

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Grades/Types of Plywood

• 5 basic grades from best to less desirable
  finished appearance A, B, C, C plugged, D
• 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

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APA Engineered Wood Products

• APA American Plywood Association key
  organization for plywood information
• Website link
• http//www.apawood.org/

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Other Panels

• Waferboard
• Composite
• Particleboard
• OSB (Oriented Strand Board)

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Plastics

• 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

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Thermoplastics
Chemical Name Properties Forms/Uses
Acrylics (Plexiglas) Transparent, hard, weather-resistant, shatter resistant, easily scratched Cast sheets/Window skylight glazing
Polyethylene Flexible, tough, translucent, low cost, easily scratched Film thickness measured in Mils Film sheet/Vapor barriers, building enclosing Open mesh/ window screen
Polystyrene (Styrofoam) Hard, clear, brittle, water- and chemical-resistant, low cost good insulating properties Tile sheet/Wall covering tile
Vinyls Poly-Vinyl Chloride (PVC) Tough, wear- and stain-resistant Tile sheet/Floor wall tile, sheet covering Coated glass fiber/ window screen Plumbing Parts
Polyamides (Nylon) Tough, hard, wear-resistant, expensive Cast/Rollers Bearings
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Thermosetting
Chemical Name Properties Forms/Uses
Alkyds Weather-resistant, tough, good adhesive properties Liquid and solid/Surface coatings such as paints, enamels, molded products
Melamines Hard, durable, abrasion-resistant, chemical- and heat-resistant Sheets/Decorative laminates, high-pressure laminates, countertops
Polyesters Weather- and chemical- resistant, stiff, hard Corrugated and flat translucent laminates, woven glass reinforced/ Window glazing skylights
Epoxy Resins Applied by using brush, trowel, or spraying equipment Waterproofing, joint sealers, protective coatings, adhesive