UNIT 1: WOOD CONSTRUCTION

1.1 LOCAL WOOD1.2 TYPES OF WOOD FINISHING AND THEIR

USES1.3 TYPES OF SOLVENT AND THEIR USES

1.4 CARPRENTRIES AND JOINTS

1.0 INTRODUCTION

Wood are being used for:i. As construction material – column, slab,

wall, beam, bridge etc.ii. As furniture’s making materialiii. As tools and handlesiv. As turnery tools and toysv. As plywood fibersvi. Main material in producing papers

Advantages of wood:i. Dry wood has good insulating properties

against heat, sound, and electricity.ii. An esthetically pleasing material (grain

patterns and colors)iii. Easily shaped, repaired, remodelediv. Resistance– oxidation, acid, saltwater, shockv. Can be combined with almost any other

material

1.1 LOCAL WOODS

Softwood – Damar MinyakHeavyweight Hardwood – Cengal, Balau/

Selayan Batu, Kekatung, Merbau, Tembusu & Resak

Medium Heavyweight Hardwood- Kapur, Kempas, Keruing & Tualang

Lightweight Hardwood – Jelutung, Meranti, Nyatuh, Ramin, Sepetir & Latex wood

Softwoods

Available directly from the sawmill, wholesale and retail yard, or lumber broker

Uses in construction for forms, scaffolding, framing, sheathing, flooring, paneling, poles, piles & other building components.

Hardwoods

Used in construction for flooring, architectural woodwork, interior woodwork and paneling.

Available from lumberyards and building supply dealers.

Most hardwood lumber & dimension stock are remanufactured into furniture, flooring, pallets, containers and blocking.

Wood classification

Category

Name Density (kg/m3)

Strength Pressure (N/mm2 )

Uses

Heavy & Hard

Grade A

Cengal, Balau/

Selayan Batu

KekatungMerbauResak

Tembusu

993 1027

847

9.979

11.38 9.17

4.9 – 11.45 8.00

-heavy construction, frames of boats, decking flooring, and utility furniture - furniture, fine joinery, turnery, cabinets,flooring, musical instruments, and specialty items.

Cont….

Category Name Density (kg/m3)

Strength Pressure (N/mm2 )

Uses

Medium-heavy & Hard

Grade B

Kempas

Keruing

Kapur

Tualang

926

791

875

7.52

4.34 – 9.17

6.74

8.0

-heavy construction work, railroad crossties, and flooring. -general construction work, framework forboats, flooring, pallets, chemical processing equipment,veneer and plywood, railroad crossties (if treated), truck floors, and boardwalks.

Cont….

Category Name Density (kg/m3)

Strength Pressure (N/mm2 )

Uses

Light and Hard

Grade C

Nyatuh

Jeluntung

Meranti

Ramin

Sepetir

Kayu Getah

758

707

657

707

2.65

3.38

5.93

4.69

-sculpture and pattern making, wooden shoes, picture frames, and drawing boards.- joinery, furniture and cabinetwork, mouldingand millwork, flooring, and general construction.

Soft

Grade D

Damar Minyak

Veneer, plywood, furniture

Standard Sized Wood Production

No

Types of wood Measurement

1.

2.3.4.

5.6.

7.

Timber

ColumnBig sawn timberSawn wood

BattenSmall batten

Laminated wood

Raw wood taken directly from lumberjacks without sawn.100mm x 100mm-150mm x 150mmThickness > 100mm x wide > 150mmThickness 12mm-37mm x wide > 150mmThickness 37mm-100mm < 150mmThickness 20mm-37mm x 25mm-75mmThickness < 20mm x wide< 100mm

Wood Drying Process

Timber have a moisture content (12 – 15%)Normally, a well dried timber has a

moisture content of 12 %If MC > 20% - defects will eventually take

place - lead to structural failureIt is important for the material to be

seasoned and preserved before being used for building construction.

Wood is either air-dried or kiln-dried.

Primary aim in seasoning timber is:i. Increase strength, toughness, and workabilityii. Decrease the possibility for the wood to splits,

shrinks as well as twist.iii. Minimize defects such as warping, bowing,

cracks after used.iv. Prevent from the fungal rots, insect

infestation, and termite attackv. Reduces the weight of timber and lessens the

transportation and handling costs.

a) Air- Drying (Natural Process)

Drying the wood by exposing it to the air

Technique: making a stack of sawn wood (separated by stickers) on raised foundations, in a clean, dry and shady place.

Cont….

Rate of drying depend on:i. Current climate conditionsii. The air movement (exposure to the wind)iii. Types of woodiv. Moisture content of the woodv. Stacking techniqueDisadvantages:i. Takes longer time up to 6 – 12 monthii. Temperature, relative humidity can not be

controllediii. The quality of dried woods are not uniform

b) Kiln Drying

The process of kiln drying consists basically of introducing heat.

This may be directly, using natural gas and/ or electricity or

Indirectly through steam-heated heat exchangers.

Cont….

Technique: wood is stacked in chamber

(wood drying kilns) which are filled with equipment for manipulation and control temperature & relative humidity.

Rate of drying depends on deliberate control temperature, relative humidity & air circulation.

Disadvantages: high cost (operational & maintenance)

Cause of timber/ wood defects

Naturali. Types of soil composition and the climate may

cause defects (split, checks, twists).ii. Lichen may grow on the surface, lead to its decay.iii. Insects destroy wood. Side Factori. Defect may also occur during drying process

(improper stacking, uneven drying, over high temperature) or

ii. During timber process (machine or handling) – causing wane, checks and splits.

Common types of wood defects

Wood Defect

Graphic Features Caused By

Bow A curve along the face of a board that usually runs from end to end.

Improper storage. Usually moisture evaporation from one side and not the other.

Twist The end twist in opposite directions. (Like twisting a towel)

Growing conditions, uneven drying or the presence of reaction wood

Rot and Decay

(Wormholes )

Small holes in the wood

This is caused by insects boring through the wood

Cont…Wood Defect

Graphic Features Caused By

Dead or Loose Knot

A dark, usually loose knot.

This is caused by a dead branch that was not fully integrated into the tree before it was cut down.

Check or Splits

Breaks at the end of a board that runs along the grain. Checks and splits are usually restricted to the end of a board.

- Rapid Drying- Growing conditions- Improper handling

Gum, Sap, or Pitch

Accumulations of a resinous liquid on the surface or in pockets below the surface of wood.

- Injury to the tree- Sometimes happens when a feeding insect damages the living part of the bark.

Wood Defect

Graphic Features Caused By

Wane The presence of bark or the absence of wood on the corners of a board is called wane.

- This defect will only be found in lower grade lumber- Improper handling

Cup - The ends of the boards will look like the letter U-

- This defect can be caused when one board face dries at a faster rate than the other.

Crook Warping along the edge from one end to the other.

Can be caused by improper drying and storage or the presence of reaction wood

Technique of Wood Preservation

Brush and Spray Treatments Brushing and spraying is done on the surface of the

timber. By using the spray method, coal-tar creosote, oil-borne

solutions and water-borne salts (to some extent) can also be applied.

A thorough brush or spray treatment with coal-tar creosote can add 1 to 3 years to the lifespan of poles or posts.

Two or more coats provide better protection than one, but the successive coats should not be applied until the prior coat has dried or soaked into the wood.

The wood should be dried before treatment.

Cont….

Dipping Dipping consists of simply immersing the wood in

a bath of creosote or other preservative for a few seconds or minutes.

Similar penetrations to that of brushing and spraying processes are achieved.

It has the advantage of minimizing hand labor. It requires more equipment and larger quantities

of preservative and is not adequate for treating small lots of timber.

Steeping In this process the wood is submerged in a tank of water-

preservative mix, and allowed to soak for a longer period of time (several days to weeks).

The depth and retention achieved depends on factors such as species, wood moisture, preservative and soak duration.

The majority of the absorption takes place during the first two or three days, but will continue at a slower pace for an indefinite period.

As a result, the longer the wood can be left in the solution, the better treatment it will receive.

When treating seasoned timber, both the water and the preservative salt soak into the wood, making it necessary to season the wood a second time.

Types and uses of Wood

Plywood i. Plywood is a laminated

product. ii. Plywood panels are made

by gluing several veneers, or thin sheets, of wood together, alternating the direction of grain with each sheet.

iii. Plywood is economical for use in subfloors and wall and roof sheathing, or under layers.

Lumber & Timberi. Both are primary construction materials for

homes and other low-rise buildings. ii. These solid woods are also used for building

boats, stringed instruments, woodwinds, and furniture.

iii. Produced by sawing tree trunks into rectangular pieces,

iv. solid wood products retain the grain and other characteristics of the tree from which they are cut.

Glued productsi. Another way of using wood

is to laminate, or layer, many pieces together with glue.

ii. Sometimes lumber is laminated with the grain of all the layers running the same way to create a beam much larger than could be cut from a single tree.

iii. Such beams are often used in the buildings with high ceilings or wide rooms.

Fiber productsi. Sometimes the form of wood

is so changed that it is not recognized as a forest product.

ii. One such form is a panel made from a pulp produced by breaking wood fibers apart.

iii. The heavy pulp is then glued into strong, thin panels for such products as pegboard and the bottoms of drawers.

1.2 TYPES OF WOOD FINISHING

Waxi. The oldest, and in some ways the best. ii. Wax is the easiest to apply, least expensive,

fastest drying, easiest to repair, and with proper care will survive forever.

iii. Wax is spread in thin coats for a surface protection after the stain and/or sealer is applied (final layer), then buffed to the desired smooth shine.

Shellac i. Shellac is one of the few

natural resins (from Lac Bug’s dung) still in use today.

ii. The big advantage is that Shellac is alcohol based which makes it very fast drying.

iii. Because Shellac is fast drying it is less likely to collect dust like varnish.

iv. This finishing also requires that you work fast with your brush and maintain a wet edge.

Lacquer i. Lacquer is used most often in furniture

factories because its fast drying properties reduce dust related finish problems.

ii. It is usually applied with a spray gun although “brushing lacquers” that cure slowly are also available.

Paint i. Paint is used in various construction as well as

production in order to provide layer to material such as wood, concrete, bricks, steel and others.

ii. Paint is used to protect, decorate (such as adding color), or add functionality to an object or surface by covering it with a pigmented coating.

iii. Paint contains binder, which imparts adhesion, binds the pigments together, and strongly influences such properties as gloss potential, exterior durability, flexibility, and toughness.

1.3 TYPES OF SOLVENT

Solvents are thicker liquids that dissolve and will interact with other liquids to achieve a specifically designed purpose.

In some cases, the solvent solution will be employed as a cleaning agent.

In other instances, the solvent will permeate a surface and provide a degree of protection.

A solvent may also offer a degree of lubrication as well, although this type of solvent usually only lasts for a short period of time.

Turpentine As a solvent, turpentine is used for thinning oil-based paints, for

producing varnishes, and as a raw material for the chemical industry.

Spirit White spirit, also known as Stoddard solvent, is a paraffin-derived

clear, transparent liquid which is a common organic solvent used in painting and decorating. Also being used to thin shellac.

Thinner A thinner is a solvent used to thin oil-based paints, or as a cleaning

agent.

Kerosene Used for thinning lacquer

1.4 CARPENTRIES AND JOINTS

LAP - The easiest to construct but needs nails or screws with the glue to provide strength. The end grain of one piece will show from one side or the other.

MITER - best looking as no end grain shows but it is more difficult to construct as the 45° angles must be cut accurately. Finishing nails are usually needed with glue to strengthen the joint.

TONGUE & GROOVE - Stronger than the LAP joint but requires more work to create. This joint works well on horizontal pieces like drawer supports or shelves.

Cont….

DADO - Stronger and better looking than the LAP joint and finishing nails can be hidden easily. This joint works well on recessed drawer fronts.

DOVETAIL - The strongest of the joints shown as the two pieces interlock. This joint requires much more work to construct but is considered high quality. This joint can be used on all corners but is typically found in drawer construction.

MORTISE & TENON - very strong and takes considerable work to construct. This joint works well for connecting chair or table rungs to legs.

DOWEL - very strong and requires care in locating the holes for the wood dowels. The dowels are usually made from .25" diameter birch or maple. This joint is typically used to join boards along their long edges.

Other types of wood joints