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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 con’t
Wood (Lumber) Decay/Insects Grading Sizing (Nominal vs. Actual) Joints Fasteners
Prefabricated Wood (Glue-laminated)
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Major Topics con’t
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 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
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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
Knot
Wane – irregular rounding caused by cutting too close to outside of log
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 >2” 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
See page 330 Section 6.2.2.2 for explanation on how to calculate board feet
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Pop Quiz – provide answers to the following:
1. What is the standard unit of measure for lumber?
2. Calculate the board feet in a 2” x 4” stud 8’-0 long
3. Find the board feet in 60 pieces of 2” x 10” joists 14 feet long.
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Pop Quiz Answers1. 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 feet5.3 Board feet (rounded off)
ORThickness (in) x Width (ft) x Length (ft) = Board Feet2 x 4/12 x 8 = Board feet2 x .333 x 8 = Board feet5.3 Board Feet (rounded off)
3. Number of pieces x Thickness (in) x Width (ft) x Length (ft) = Board Feet60 x 2 x 10/12 x 14 = Board feet60 x 2 x .833333 x 14 = Board feet1400 = Board feetOften written as 1.4 MBM [1.4 Thousand Board Measure]
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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) 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
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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)
• See Figs. 6.2-20,-21, and -22 – on pages 335-36 for examples of grade marks
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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”
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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
**** There are a variety of nailing methods used:
Toe nailing, end nailing, face nailing, blind nailing
**** Standard sizes of common wire nails
See page 361 for Figures 6.6-2
and 6.6-3
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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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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
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Species of Lumber Used for GlueLam
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) 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 (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
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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
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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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Chemical
NameProperties 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
Thermoplastics
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Thermosetting Chemical
NameProperties 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
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References
Construction Materials and Processes, 3rd Edition. Watson, Don A.. McGraw-Hill, 1986. Imprint 2000. ISBN: 0-07-068476-6
Construction Principles, Materials, and Methods, Seventh Edition. H. Leslie Simmons, John Wiley and Sons, Inc., 2001.
Olin’s Construction Principles, Materials, and Methods, Eighth Edition. H. Leslie Simmons, John Wiley and Sons, Inc., 2007
Architectural Materials for Construction, Rosen, Harold J. and Heineman, Tom. McGraw-Hill, 1996. ISBN: 0-07-053741-0
Basic Construction Materials, 6th Edition. Marotta, Theodore W. Prentice Hall, 2002. ISBN: 0-13-089625-X
Building Construction: Materials and Types of Construction, 6th Edition, Ellison, Donald C., Huntington, W.C., Mickadeit, Robert E.. John Wiley & Sons. ISBN: 0-13-090952-1.
Architectural Graphic Standards: Student Edition, Abridgment of 9th Edition. The American Institute of Architects. John Wiley & Sons. ISBN: 0-471-34817-1
