Wednesday, September 17, 2014

Review Notes: Building Materials - Wood and Wood Products


Wood – a traditional building material, it is easily worked, has durability and beauty. It has great ability to absorb shocks from sudden load. In addition, wood has freedom from rust and corrosion, is comparatively light in weight, and is adaptable to countless variety of purposes.

Classification of Trees:
1. Hardwoods – ‘deciduous’ trees that have broad leaves which are normally shed in the winter time.
2. Softwoods – ‘conifers’ trees that have needles rather than leaves and that bear their seeds in cones.

Moisture Content of Wood – expressed as a percentage of the oven-dry weight and can be determined by the oven-dry method or by an electric-moisture meter method.

Three categories of Lumber:
1. Yard Lumber – used for ordinary light construction and finishing work and consists of 1 and 2 inches material manufactured into common boards, shiplap, shelving dimension lumber, center match, flooring, roof plank, siding, v-joint, trim and molding of all kinds. These are usually found in retail lumberyards.
2. Shop Lumber – usually left in 1 and 2 inches rough thickness often containing knots or defects not ordinarily permissible in other categories. It is intended for use in shops or mills making sash, doors and cabinets where it will be cut into relatively short pieces and the defective material discarded.
3. Structural Lumber – in intended for use in heavy construction for load-bearing purposes and is cut into timbers of large size than yard lumber, 3 inches or more thick and 4 inches or more wide. It is made from the heartwood of the log.

Finishes of Wood:
S1S – surfacing or planning of one side
S2S – two sides planed
S4S – four sides planed
Rough – as sawn and not planed

Wood Grain:
1. Edge Grain – annual rings run approximately at right angle to the face.
2. Flat Grain – when the annual rings run more or less parallel to the surface.
3. Angle Grain – when the annual rings are at about 45 degrees to the face.

Seasoning of Lumber:
1. Air-Drying – lumber is strip-piled at a slope on a solid foundation. This allows air to circulate around every piece while the sloping allows water to run off quickly.
2. Kiln-Drying – more expensive lumber which is required for more refined uses so as wood will not move, such as furniture. Flooring and general interior use.
Pressure treated lumber – when lumber is subjected to pressure and injected with chemicals or salts to insure it from rots.

Specification when buying lumber:
Indicate no. of pieces, thickness, width, length, total bd. Ft. kind of lumber and finish.
Example: 6-2” x 8” x 14’-0” = 112 bd. Ft. tanguile S4S

Glue laminated timber – term used to describe a wooden member built up of several layers of wood whose grain directions are all substantially parallel, and held together with glue as fastening commonly used for beams, girders, posts, columns, arches, arches, bowstring truss chords, usually softwoods are commonly used because of their low cost, lightness and strength.

Glue use in laminating:
1. Casein glue – satisfactory for use in dry locations not exposed to rain or water.
2. Urea-formaldehyde-resin – cheap and well cure at from 70 degrees Fahrenheit up. Will withstand soaking in cool water.
3. Phenol-formaldehyde-resin glues – not usually recommended because of the high temperature needed to cure them. Useful for combining timber and plywood and are very water-resistant.
4. Resorcinol-phenol-formaldehyde – resin glues are expensive but have excellent qualities of durability and water resistance.


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