Materials

Question 1

What is the definition and some examples of the following types of timber:
– Native
– exotic
– imported

Answer 1

Native – timber that originated in grows in New Zealand. Examples are rimu, kauri, totara, tawa and matai.

Exotic – is timber that is not native to New Zealand but as grown here. Examples are pine, Douglas fir, macrocarpa and Cedar.

Imported – is timber that is grown in other countries and imported to New Zealand. Examples are Pacific rimu, American oak, Cypress, jarrah, kwila and sapele mahogany

Question 2

What do the following abbreviations mean in relation to timber:
– RS
- D4S
- PG
- T&G
- TG&V

Answer 2

RS - rough sawn
D4S - Dressed four sides.
PG - planer gauged
T&G - tongue and groove
TG&V - Tongue and groove with a bevel

Question 3

What is the purpose of a finger joint and where are they used?

Answer 3

Fingerjointing is used to create timber of regular lengths. Short lengths are joined end to end and then machine to profiles that are commonly used such as finishing trim, weatherboards, facias and facings, scribers and cavity batons.

Question 4

What is pre-primed timber?

Answer 4

Timber that is pre-primed is mostly finger jointed and generally used for exterior building components such as weatherboards and facings. The timber has been treated to H3 .1 and then pre-primed to protect The preservative. Additional coat of paint must be applied after installation as the primer is not designed to withstand continued exposure even for a short period of time.

Question 5

What is laminated veneer lumber (LVL)?

Answer 5

LVL is made from layers of timber veneers that are glued and press together with the grain running parallel along the length. They’re available in lengths up to 600 mm. LVL has structural components offering strength and stiffness that make some suitable for beans and rafters and can be manufactured to specified curves and shapes.

Question 6

What is glue-laminated timber(Glulam)?

Answer 6

Glulam is made from layers of solid milled timber that is glued and press together with the grain running parallel along the length. They are generally used for lintels beams and bearers.

Question 7

What is cross laminated timber (CLT)?

Answer 7

CLT is made up from layers of solid milled timber glued and press together with a grain of each layer running at 90° to the previous layer. There is an odd number of layers to create a strong and rigid product which has the same appearance on each side as a central layer. CLT is a panel product and his comes in size up the 15m long and specified for floors, roofs and ceilings were it offers high levels of airtightness thermal and sound insolation and fire resistance.

Question 8

What is laminated Strand lumber (LSL)?

Answer 8

LSL is a reconstituted timber product with small pieces of timber is pressed together with a mix of adhesive steam and pressure. LSL of similar strength to LVL though it is cheaper to specify and generally less favoured in applications where it maybe visible in the finished product.

Question 9

Why is timber seasoned?

Answer 9

Seasoning is the process of drying timber which is crucial for insuring the stability of timber for use in the building industry. Timber is suitable for use when the moisture contained with in the timber is the same as in the surrounding area this is called equilibrium moisture content (EMC).

Question 10

How is timber season?

Answer 10

Air drying – this is when the timber is left to dry in its natural environment however it occurs slowly because timber naturally absorbs and releases moisture depending on the moisture levels in the surrounding atmosphere.

Kill drying – Is the most common way timber is seasons for use in the building industry it is done in a manufactured environment where the temperature and humidity can be controlled.

Question 11

Why is the moisture content of timber important to builders?

Answer 11

Green timber that has not reached the EMC is likely to shrink as it dries which will lead to gaps after it is installed. It may also cause moisture to be release into the plasterboard.

Question 12

What tests are done to ensure timber is at EMC on site?

Answer 12

A pre-line inspection the inspector makes random tests of the framing timber using a moisture meter to check that the moisture content is 18% or less before signing off to approve the installation of linings.

Question 13

Where is H1 timber used and what is it treated for?

Answer 13

H1 timber is used in situations that are protected from the weather. The main purpose of this treatment is to protect the timber from attack by wood boring insects. The main chemical used is boron.

Question 14

Where is H3 timber used and what is it treated for?

Answer 14

H3 timber and plywood is used on exterior situations that are exposed to the weather but not in contact with the ground.

H3.1 timber is coated with a three coat paint protection system such as facias weatherboards and facings. H3.2 is not paint protected such as fence rails, palings and decking.

The main treatment use a copper based chemicals and light organic solvent preservatives (LOSP).

Question 15

Where is H4 timber used and how is it treated?

Answer 15

H4 timber, roundwood and plywood is used in situations where there is contact with the ground or continuous severe waiting such as fence posts and landscaping timber. The main chemicals used in this treatment are copper based chemicals

Question 16

Where is H5 timber used and how is it treated?

Answer 16

H5 timber, round wood and plywood is used in situations where there is contact with the ground or continuous severe wetting and where the uses are critical and a high level of protection is required such as house piles or retaining walls. The main chemicals used in this treatment a copper based chemicals.

Question 17

How is timber treated?

Answer 17

The way a preservative treatment gets into timber is either by exposing the timber to the preservative through dipping or spraying or through a process that uses a vacuum or pressure. Timber is treated against insect/fungal attack and exposure to moisture. The treatment varies according to the end use.

Question 18

What are the four recognised classifications for grading timber?

Answer 18

• Appearance grades used for cladding, furniture, finishing and non-structural components.
• Structural grades used in building where strength and stiffness are required.
• Cutting grades which are short lengths clear of defects used for furniture and specialty components.
• Box grades used for boxing, pallets and packaging.

Question 19

How is building timber graded?

Answer 19

Timber used for building is graded by machine. The timber is bent to a preset point and if it doesn’t break, it passes that grading level. The grades that relate to the strength of the timber used to build framing are generally machine stress grades(MSG) where the timber is stamped or coloured to show the grade.

Question 20

What are the grades for the common types of timber used in building?

Answer 20

Most structural timber framing must be MSG8 or better, While items like ceiling batons can be MSG6. Exact requirements are specified by designers.

Question 21

What is the process relating to the visual grade of timber?

Answer 21

Visual grading of timber by qualified timber graders is used to assist the timbers suitability for induced rather than at strength. Visual grading identifies defects and the size or severity.
Pieces of timber with no notes or other defects are referred to as clears.The lowest grade of timber available is merchant (merch) or box in grade timber.

Question 22

What are the four typical defects in timber

Answer 22

Knots – these are the circular remnants of branches. Knots can compromise the strength of structural timber and damage its appearance.

Checks – these occur with timber fibre shrink during the drying process and create cracks lengthwise in the grain. They are generally surface only but may extend right through the finish timber.

Warping – this is the distortion of a piece of timber usually caused by uneven driving and include:
– bows which occurs in the length of boards on the flat
– crooks which occurs in the length of the boards on the edge
- Cups which occurs across the width of boards
– tap twists which is a spiral distortions along and across boards

Insect damage – occurs from insects laying eggs on timber that is in eaten away by the larvae also can be caused by would boring insects.

Question 23

What causes decay and what are the two most significant types of decay?

Answer 23

Timber exposed to moisture for extended periods of time may become infected by wood fungi that causes various types of damage. Wood fungi causes decay/rot, wood staining and mold.

The two most significant types of decay are Wet rot and Dry rot.

Question 24

What is wet rot?

Answer 24

This fungus attacks a timber that is very wet and is often found in buildings that have had an undetected water leak. The wet rot fungus needs a high moisture content to survive and spread. If the timber dries out the fungus dies and it’s easy to get rid of timber with rot by simply cutting the wet timber out.

Question 25

What is dry rot?

Answer 25

Dry rot fungus survives in badly ventilated areas where there is little or no air movement around damp timber. Dry rot is often found where timber has been poorly isolated from cement base products such as concrete blocks and mortar. The fungus makes the timber dry and crumbly, and spreads by sending out thin strains into the good wood.
When a rotten portion is removed, a margin of seemingly good timber on either side of the rot should be removed to remove all the fungus. An appropriate liquid treatment should be applied to the cuttings of both the original and the new timber before installation

Question 26

How does ultra violet light effect timber?

Answer 26

Ultraviolet light alters the cell structure in the surface of timber and changes its appearance and surface quality. This can cause checks in the surface. Surface coating such as paints and stains assist in managing this process.

Question 27

How can chemicals effect timber?

Answer 27

Timber is highly absorbent and relatively easily damaged. Timber that is exposed to strong acids and alkalis breaks down and cause the wood fibres to separate and turn into pulp.

Question 28

What is a butt joint and where are they used?

Answer 28

A butt joint is where the flat end of a piece of timber is joined to the face, edge or end of a second piece of timber. Butt joints occur in framing of all kinds and also with skirting meets and architrave or finishing trim meets a wall in an internal corner.

Question 29

What is a mitre joint and where are they used?

Answer 29

A angled joint, Normally 45°, use mostly when installing interior trims.

Question 30

What a lap or halved or splice joints?

Answer 30

It was used to join two pieces of timber of the same thickness. Each piece was cut so that half the timber thickness remained and when the two halves were brought together the thickness at the joint was the same as the original timber thickness. Lap joints were used end to end along walls, at right angles were to walls meet and at right angles were two walls crossed. Lap joints are most commonly used now for landscaping and fencing applications.

Question 31

What is a rebated joint?

Answer 31

Effectively a lap joint in panel products such as plywood. One edge of the panel is rebated on the front and the other edge is rebated on the back when installed one overlaps the other.

Question 32

What is a birds mouth?

Answer 32

Birds mouth as we are an angle check is cut out of a rafter so that it sits on top of the top plate of an external wall. It is made up of a seat cut that sits on the top plate and a plumb cut the rest against the outer edge of the top plate.

Question 33

What is a tongue and groove join?

Answer 33

Accurate fitting of the machine tongues into the matching grooves create a strong sheet like membrane. Tongue and groove joints associated with flooring a caaled T&G. Tongue and groove joints associated wall panelling a cool TG&V as they have chamfered edges on the front faces that form a V when the tongues and grooves are engaged.

Question 34

What is a mortise and tenon joint?

Answer 34

Mortise and tenon joins are traditionally used by joiners and carpenters to join two pieces of timber at 90°. The mortise is a rectangular hole in the face of one piece of timber and the tenon is a matching tongue on the end of the other. Some are cut right through with slotted tenons protruding beyond the timber end. Wedges are driven into the slots to tighten the tenon in place before it is trimmed to finish flush with the end of the timber. Mortise and tenon joins are found in timber doors and windows with the rails are mortise and the styles are tenons.

Question 35

What our housing joints?

Answer 35

Housing joints are where are one timber item is cut to match and accept (house) the profile of another member. A form of housing joint is used in stair making. The stringers are checked to house the treads and rises of the stairs which are glued and wedged in place. Checking the treads and risers into the stringers means at each end is supported. The bottoms of tread housings in the backs of riser housings a tapered to accommodate wages.

Question 36

What are dowelled joints?

Answer 36

Dowelled joints use a cylindrical piece of timber with chamfered ends that is placed in holes of the same diameter and two opposing pieces of timber to join them. The dowel helps to hold the joint together by increasing the surface area of the glue joint to create additional strength. Some dowels have longitudinal ridges to further increase surface area for the adhesive.

Question 37

What are biscuit joints?

Answer 37

Biscuit joints have mostly replaced dowelled joints for the manufacture of joinery such as commercial office furniture because they are simpler to machine and prepare and easier to assemble. The biscuits used in the joints are made from compressed timber fibres and can be used in most furniture and joinery joint situations.

Question 38

What are dovetail joints?

Answer 38

Dovetail joints corner joints with angle cut interlocking fingers. These are most commonly used in the manufacture of furniture components such as drawers.

Question 39

In relation to screws what is represented by the gauge number?

Answer 39

The diameter of the screw.

Question 40

What is a cyclone/tiedown strap?

Answer 40

Cyclone or tiedown straps a light weight steel straps that come in a range of styles and configurations. They have a standard purpose which is to tie one component down to another especially in Highwinds zones. Examples include trusses to the top plate purlins to trust or joist to bearer.

Question 41

What are tensioning straps?

Answer 41

Tensioning straps are made from lightweight metal sheet with holes pressed out to allow them to be nailed. They are generally used in roof framing and run diagonally over the plane of roof and tensioned to brace the roof square.

Question 42

What are timber connector plates?

Answer 42

Timber connector plates use large numbers of small nails to connect timber members end on end. Nail plates have many punch out prongs that are pressed into the timber by the frame and truss plant or by hammer on site. Nylon plates have punched holes in them to allow for nailing by specified fixings.

Question 43

What are hangers?

Answer 43

Hangers a metal brackets for fixing timber beams such as joists at right angles.

Question 44

What are post and bearer brackets?

Answer 44

Post and bearer brackets are typically made from a heavier weight steel, 3 to 5 mm thick and are either galvanised or stainless steel. They are used to connect heavy components such as pergola or Veranda posts or bearers to other surfaces such as concrete slabs or masonry walls. They connect the two structurally while at the same time keeping timber physically clear of the concrete surface that could contribute to dampness and decay.

Question 45

What are contact adhesive?

Answer 45

These are adhesives are all based on polymers that bond to themselves as dry adhesive films. Once both surfaces are coated in the adhesive has skinned they are placed together for an instant bond with high initial strength. All wall board and other construction adhesive used for fixing plasterboard and other linings, flooring or laminates amongst the myriad of other uses are contact adhesives. So is the brush on version that might be used to install flashing tapes.

Question 46

What are a epoxy resin adhesives?

Answer 46

Epoxy is come from a family of polymers that react and cure by contact with a range of compounds which are referred to as hardners. The epoxy resin has excellent get filling qualities and cure under wide range of conditions. They are heavy duty adhesives that are most commonly used along with steel fixings to form chemical anchors to connect construction components to concrete and masonry.

Question 47

What are metallic coatings in terms of protecting steel?

Answer 47

A number of metallic coatings are applied to steel to protect the surface and provide a specific finish. Structural steel is typically galvanised to provide some corrosion resistance. Electroplating and sherardising other processes used to coat steel.

Question 48

What are the protective paint systems in relation to steal?

Answer 48

Spray systems – involve spraying a liquid compound over the steel. Some spray coatings dry and hard and by the evaporation of solvent and others have a hardner added, which causes a chemical reaction to produce a hardened surface.

Electrostatic coating systems – involve spraying at powder or liquid compound towards the steel component. The component is more affectively coated than with standard spray painting because the sprayed coating is attracted to the component on all sides by a powerful electrostatic charge. The finish is most often baked in aN oven after spraying.

Question 49

How is concrete strength measured?

Answer 49

Concrete strength is measured in megapascals (MPA). A common mix used on the floor slabs, piles in fence post is 17.5MPa, although stronger mixes are also used. Concrete strength is adjusted by changing the cement slant aggregate ratio, and by using additives.

Question 50

What are the common types of finishes for concrete?

Answer 50

Screeded– we are the concrete is left to cure after screening.
Brushed – where the surface is screeded and floated, then lightly brushed for a low slip finish.
Floated – where the surface of smoothed off with a steel float.
Coloured – where the colour is added to the concrete, or spread over the floated concrete after it has been placed.
Stamped/stencilled -Where the concrete is stamped or stencilled with a repetitive pattern for a decorative finish.
Exposed aggregate – where the concrete is left to partly cure, then the fines are removed from the surface leaving the aggregate partly exposed.
Textured surface – we are fine Garrett is spread over the surface to provide a low slip finish

Question 51

What are the common defects in concrete?

Answer 51

Defects and fresh concrete include:
– cracks caused by the surface drying to quickly or insufficient reinforcing.
– Chips or broken edges is caused by removing the formwork too early in the curing process.
– Stains to the surface cause by foreign matter in the concrete mix or on the surface.
- Bubbles in the concrete cause by insufficient vibration.
- Bleeding caused by excessive floating of the concrete.

Question 52

What is the purpose of reinforced concrete?

Answer 52

Concrete floor slabs must be reinforced to help prevent cracking, to increase the load-bearing capacity of the floor slab and to provide additional rigidity to the concrete floor and any walls that are made from concrete or concrete products. Reinforcing steel is installed into the foundation before concrete is poured.The reconfiguration of the steel is determined by the designer or engineer.

Question 53

What is precast concrete?

Answer 53

Precast concrete elements are mostly manufactured offsite to us to a set of specifications and delivered to site ready to install. The precast elements are cast in moulds that are potentially reusable and cured in a controlled environment before being delivered. A lightweight version of precast concrete panels uses crushed pumice in place of standard aggregate. The pumice significantly reduces the weight of the panels and also introduces a built in insu factor. These components are used in both residential and commercial construction.

Question 54

What is aerated concrete?

Answer 54

Aerated concrete is available in panel and block form. This concrete has no aggregate larger than sand. It uses aluminium powder which reacts with calcium in the mix to produce large bubbles of hydrogen. The product is removed from the mould while still soft and baked in autoclave at about 200°C for 12 hours. The hydrogen escapes and is replaced by air. Aerated concrete is about one quarter of the weight of regular concrete and he’s about half the compressive strength.

Question 55

What is prestressed concrete?

Answer 55

Prestressing involves tensioning high-strength steel tendons known as stressing strains within cast concrete components in order to increase the structural capacity of the components. Prestressed concrete is used in a number of large-scale projects such as bridges in high-rise buildings, mostly in commercial, industrial and infrastructure construction.
Common prestressed elements include beans, columns, hollow core panels in pre-chambered four sections.

Question 56

What are some of the most common cast in items in precast concrete?

Answer 56

• Lifting eyes or anchors
• Welding plates
• Corrugated tubes to accept reinforcing from existing structures.
• Chairs that whole reinforcing steel in place
• Reinforcing steel to provide tensile strength
• Threaded inserts providing fixing points for structural members and other fittings that are bolted directly to the concrete structure

Question 57

What are epoxies?

Answer 57

Epoxy’s are groups of chemical reasons used with catalyst and hardner that preform a range of functions. Typically they are found in adhesives, sealers and finishes such as two pot varnishes and paints. Chemical anchors are systems where steel studs and bolts are bonded into the substrate, usually masonry or concrete, using epoxy adhesives.

Question 58

What are silicones?

Answer 58

Silicones are polymers that mostly stable, non-toxic, flexible, rubber like and heat resistant. In the building industry they are widely used as sealants and adhesives. Manufacturers instructions assist in identifying the correct uses for silicones, some of which perform poorly when in contact with various materials.

Question 59

What are examples of plastics that are used on a construction site?

Answer 59

– Polythine used as underlays, pipes.
- Polyvinyl chloride (PVC) and some roof coatings, pipes, flooring.
– Acrylic and bath, shower liners, clear screens.
– Nylon for fitting, wedges, shims.
– Polycarbonate inroof and wall cladding’s.
– Polystyrene as underfloor installation.

Question 60

What is fibreglass?

Answer 60

Fibreglass is glass reinforced plastic and is used mostly as an insulation in buildings. Recycled glass is the main ingredient in the manufacturing process. It is mixed with ingredients such as Ash, limestone and sand, and heated to melting point before being spun into long, superthin threads of glass fibre which are then bundled into matts which are chopped to size. Fibreglass is also the product used to manufacture some forms of translucent roof sheet.

Question 61

What are the different types of glass commonly used in construction?

Answer 61

Plate glass – is the standard glass that is found in most windows.
Toughened glass – has been heat treated to altar its composition. It is stronger than plate glass and crumbles into small granular chunks instead of splintering into shards. It is used in doors balustrades and low windows that are likely to receive impact.
Laminated glass – has a layer of plastic material sandwiched between two layers of glass. The glass bonds to the plastic even when broken, greatly increasing safety. Laminated glass - is used in large picture windows, balustrades and security windows and doors.