Welcome to the NZ Wood Frequently Asked Questions
- Buyers Guide (25)
- Environmental (7)
- Forestry (9)
- Pine (9)
- Processed Wood (33)
- Using Wood (47)
- NZ Wood (3)
Using Wood (47)
Information on alternatives to pine and their structural properties.
Information on Douglas-fir as an alternative solution
Visit the Species Index on the website.
Hardwood is not necessarily a harder material (more dense) and a softwood is not necessarily a softer material (less dense).
Different types of construction projects call for different kinds of timber, both hardwood and softwood are used for everything from structural to decorative.
Softwood and hardwood are distinguished botanically in terms of their reproduction, not by their end use or appearance. All trees reproduce by producing seeds, but the seed structure varies.
In general, hardwood comes from a deciduous tree which loses its leaves annually and softwood comes from a conifer, which usually remains evergreen. Hardwoods tend to be slower growing, and are therefore usually more dense.
Softwood trees are known as a gymnosperm. Gymnosperms reproduce by forming cones which emit pollen to be spread by the wind to other trees. Pollinated trees form naked seeds which are dropped to the ground or borne on the wind so that new trees can grow elsewhere. Some examples of softwood include pine, redwood, douglas-fir, cypresses and larch. (more information visit our species section)
A hardwood is an angiosperm, a plant that produces seeds with some sort of covering such as a shell or a fruit. Angiosperms usually form flowers to reproduce. Birds and insects attracted to the flowers carry the pollen to other trees and when fertilized the trees form fruits or nuts and seeds. Hardwoods include eucalypts, beech and blackwood.
The hardwood/softwood terminology does make some sense. Evergreens do tend to be less dense than deciduous trees, and therefore easier to cut, while most hardwoods tend to be more dense, and therefore sturdier. In practical terms, this denseness also means that the wood will split if you pound a nail into it. Thus you need to drill screw or bolt holes to fasten hardwood together. But structural lumber is soft and light, accepts nails easily without splitting and thus is great for general construction.
Is it acceptable to use untreated macrocarpa for fence palings, and what ground clearance is recommended?
The How-to-build guide on fencing compiled by BRANZ (based on using H3.2 treated radiata) recommends a minimum ground clearance of 50 mm.
With untreated wood the concern is that rain splash will put dirt onto the bottom of the paling, causing it to accumulate on the horizontal bottom edge. This then pushes the decay hazard above the H3.2 level. If there is fresh earth next to the palings then the dirt can be splashed higher than 50mm. If there is grass or paving then there might be no dirt splashed up at all.
Depending upon the application, therefore, it might be advisable to have a greater ground clearance than the 50mm recommended for H3.2 treated radiata.
Fencing is not a structural situation so compliance with the Building Code is generally not required if the completed structure is under 1.8mtrs high. It will also depend on what sort of a fence you are building, so check with your local council before you undertake any construction just to be sure.
See Macrocarpa on the species sectoin
More about Hazard classes
Macrocarpa is suitable for decking and does not need to be treated. Its natural durability can be sufficient for this purpose.
However, its durability is unreliable in moderate-high decay hazard situations, and occasional failures may occur within 10-15 years. Therefore it is not recommended in-ground, such as for posts and piles.
See Macrocarpa on the species section.
See the how-to guide for information on building a deck.
Kiln dried timber usually has drier and wetter pieces that will slowly adjust to whatever equilibrium moisture content is appropriate to the situation they are in.
To acclimatise the timber ‘in situ’ prior to installation, the flooring is stacked with fillets (narrow strips of wood) between each layer. It will have been delivered block stacked, i.e. without fillets.
If the house is under construction then there is little point in doing this because the ambient conditions during construction will not be those when the house is complete and occupied. Some change is unavoidable as the flooring equilibrates to the final conditions.
If, however, the flooring is to be used for an extension to an existing house then there is merit in fillet stacking it for two or three weeks to “acclimatise” (or equilibrate) and this will keep any subsequent shrinkage to a minimum.
More on moisture measurement
More on the timber drying process (focuses on pine but is applicable to other species)
The Building Act 2004 sets out the legislation on building standards and procedures. The Building legislation and regulations page of the website has detailed information on this.
Six Hazard classes are used to describe the service exposure conditions in relation to the biological hazard. They are set out in the Hazard Classes .pdf. More detail about the actual hazards is provided in the found on the Hazards page of the website.
For board and batten cladding, cedar is excellent although it is the most expensive. Imported cedar is always completely free of knots.
The second choice is heart macrocarpa. It is unlikely that there would be any or much sapwood in macrocarpa but sap macrocarpa is not durable. Knots in macrocarpa have an undesirable habit of checking but for vertical board and batten cladding that is not a problem because it will be backed with a building wrap.
Douglas fir should be durable enough for this application but there are doubts, especially if there is some sapwood on the boards.
For that use the heartwood of western red cedar, or macrocarpa would be suitable. Locally grown western red cedar is likely to be knotty and slightly less durable than imported western red cedar. Imported western red cedar has been available in clears and knotty grades but the latter sometimes include bark encased knots which are likely to come loose in service. Douglas fir is less durable, somewhat unreliable, although it has been used for external sheathing.
Untreated macrocarpa, Lawson Cypress, Lusitanian Cypress or Larch are possible options.
To achieve an “acceptable solution” within an enclosed frame H3.1 treated radiata needs to be substituted with either:
- Structural grade untreated larch, or
- Untreated heartwood from the cypress species (or H1.2 treated sapwood). Macrocarpa is the most likely source, but Lawson cypress may be available although unlikely to be in large supply. (The heartwood is easy to identify, and available, if you find a supplier of the species.)
For both of these, because they are specialist species, they could be hard to source for structural purposes ie. MSG or VSG 8 or better. Very few producers will go through the “verification” steps for small scale volumes.
If MSG 6 is sufficient then visually graded “number one frame” will be an acceptable alternative. (Unverified “number one frame” is deemed MSG 6 and it can be used in place of MSG 8 but will require larger dimensions to give equivalent strength)
That leaves “alternative solutions”:
- Research would support H1.2 boron treatment as being suitable for enclosed frames in any situation and some Building Consent Authorities (BCAs) will approve H1.2 Douglas-fir in place of H3.1 Radiata.
If it is an outdoors or exposed structural application eg. posts where 50-year durability is mandated, then the building standard NZS 3602 does not designate any commonly available untreated wood as an “acceptable solution”.
NZS 3602 allows untreated heartwood from redwood, western red cedar, cypress species and New Zealand beech for outdoor use in stairs, decking, handrails where a 15-year durability is required.
(Note: because of the risk of leaching, H1.2 boron should not be used in exposed areas unless it is primed and three-coat painted.)
For more information on treated timber and building legislation visit the Treatment and Durability section of the website.
Look at the table of alternatives to pine and their structural properties.
1.CCA treated timber has been shown in some studies to leach low levels of chemicals into the soil immediately surrounding the treated timber. Soil tested within 25 mm of the treated timber sometimes slightly exceeded advisable safety levels for arable soil.
Soil tested further than 25 mm from the treated timber showed no significantly raised arsenic levels compared to other NZ soil. (Note, background levels of arsenic in New Zealand soil are between five and nine parts per million approximately or 5-9mg/kg.)
Uptake of these chemicals by fruit and vegetables has been shown to be minimal and is within accepted international food safety thresholds.
If you are particularly concerned, it is suggested you plant no closer than 35cm to the timber edge or place a plastic or polythene barrier between vegetable garden soil and the CCA-treated timber edging.
2.Do not use LOSP treated timber – it is not rated durable for in-ground applications.
3.You could instead use untreated timber from a species with higher natural durability like macrocarpa or some eucalyptus species, however if left in contact with the ground the timber will eventually rot.
Common options for cladding include:
- Radiata pine
For radiata pine weatherboards that are clear finished or unpainted, the minimum treatment is H3.2. Painted, the minimum treatment level is H3.1.
Weatherboard cladding made from radiata pine is widely used in New Zealand, including areas with demanding climatic conditions. Because of the presence of spiral grain, the juvenile wood of New Zealand pine should not be used where stability is vital to performance. Dimensional performance can be increased by use of finger-jointing, and/or lamination. Such highly processed laminated, finger-jointed clear products are used widely in Japan where a maximum stability is required.
This is discussed in the FAQ section
- Leyland cypress
Leyland cypress is a hybrid of macrocarpa and should be even more durable. It is certainly very stable, and should be even better for cladding.
- Western red cedar
Western Red Cedar is a species commonly used in New Zealand for natural looking claddings. This is mostly imported from Canada. The New Zealand grown timber is usually regarded as inferior to the old growth timber from British Columbia, which is very stable and durable. As with all timber cladding, it is highly recommended that cedar has a protective coating of either stain or paint.
For more on wood choice, the Substrates page on the website may be of help.
In terms of finishes for the timber cladding, please see the Exterior Finishes section on the website.
It is advisable to avoid dark colours for most wood cladding. The finishes section of the website provides some guidance on light reflectance and heat generation.
Wood is fast and flexible
- Timber provides for flexibility of design, and allows modifications and tweaks to layout during the construction process. Factory pre-fabricated and pre-cut steel frames do not.
- Builders are familiar with using wood, and usually prefer it. Builders report frame construction times of two to two and a half times longer for steel frames.
- Steel frames, however, have the advantage of being able to be constructed in wet weather, and do not require the drying time of wood frames. Wood moves as it dries out.
- Wood is a lower cost raw material than steel.
Snug and sound – Thermal performance
- Wood is 400 times better as a thermal insulator than steel and 14 times better than concrete.
- In solid form, wood also has significant thermal mass properties, retaining heat from the day and releasing it at night.
- Wood also acts as a humidity regulator, absorbing moisture when humid and desorbing moisture when the air is dry.
- Read more about the thermal performance of wood
Wood doesn’t rust
- All building materials used for the structure of houses in New Zealand are required to have a minimum service life of 50 years to comply with the building code.
- Wood, used appropriately in accordance with building standards, will usually far exceed this.
- The mutual enemy of both wood and steel is moisture. Ingress of moisture into wall cavities should be minimised and the design should ensure that any moisture that does enter from leaks or condensation can drain and dry.
- Although steel is normally galvanised to protect it from corrosion, steel frames are susceptible to rust where the surface coating is cut, scratched or penetrated, and from edges that have been cut.
- Wood treated with the appropriate level of preservative, and properly maintained, can last in service for a hundred years or more.
What is the availability and suitability of indigenous or NZ grown large beams of timber for outdoor use?
The question relates to timber of cross section 200mm x 250mm for a large outdoor architectural feature. It needs to stay straight, not split or warp, and to silver off without the need for staining and other maintenance.
The size of the beams and availability could be difficult. Indigenous timbers which might have the durability (beech, totara) are not likely to be available in big enough sizes or big enough quantities. The size also means the timber could not be dried and that makes stability a problem.
A good solution would be macrocarpa or Douglas-fir heartwood glulam as the lamination will overcome any problems with knots and it will be properly dried before it is glued.
Look in our Suppliers database to search for a supplier near you.
The main issues are:
- Colour – fading, discolouration, ultraviolet effects, mould growth
New Zealand grown species that could be considered are:
- Radiata. Must be treated to H3 or H4. CCA is the only commonly available treatment that will achieve sufficient durability. An alternative to CCA would be ACQ or Cu-azole treatment but may be hard to find. (Timber treatment companies such as Osmose or Arch should be able to advise on availability.)
- Macrocarpa. Does not need treating, otherwise similar to radiata. Note: macrocarpa can be unreliable where it is fully exposed to the weather, i.e., a few pieces are likely to fail or need replacement within the 15-year minimum durability requirement.
- Eucalypts. These are mostly durable hardwoods. The Eastern Blue Gum group: (E saligna and E. botryoides) and the Stringybark group: (E. muelleriana, E. globoidea, E. eugenoides, E. microcorys, E. pilularis) are most suitable for decking.
- The heartwood of all the blue gum and stringybark species are durable in ground contact, lasting 15 to 25 years in ground contact and up to 40 years out of ground contact, giving an equivalent durability of H3.2.
Permanently shaded areas will become slippery so regular maintenance (waterblasting) is needed. Decking is usually grooved to reduce slipperiness. A surface coating of high built glassfibre-reinforced epoxy coating will overcome most of these problems. Screw fixing may be preferable to nail fixing although decking nails are resistant to popping. All timber is porous so will allow mould to penetrate and cause discolouration.
Wall linings for indoor pools
Durability is less of an issue with indoor pool wall linings. There is no danger to the wood from chlorinated water. It does not damage the wood and acts as a mild preservative. There will be discolouration though, as with any wood if it gets splashed.
Commonly available timber options would include pinus radiata, Douglas fir and macrocarpa. New Zealand-grown eucalypts could also be considered, or indigenous timber such as beech where a high end finish is desired.
With moderately durable species like the cypresses the degree of exposure is important. If the wood is wet frequently and remains damp for long periods the chances of decay within 50 years are relatively high.
Verandah posts and beams may be wet occasionally when there is rain but the surfaces exposed to wetting are usually vertical, are well ventilated and clearly visible. Therefore the risk of decay developing is relatively low. There are plenty of examples of old buildings with kauri and rimu verandah structures that are more than 50 years old.
If end grain is exposed to wetting, significant water penetration is likely. This will increase susceptibility to decay and additional protection, either with some sort of cover or with regular application of a water-repellent coating, would be advisable.
Macrocarpa (Cupressus macrocarpa), has heartwood that is in Australasian durability Class 3 i.e. in testing of ground contact 50 x 50 mm stakes it has been shown to have an average life of 5-15 years. The average life is towards the upper end of this range but a few early failures occurred in the tests. Rimu (Dacrydium cupressinum) and kauri (Agathis australis) heartwoods have the same durability classification.
Away from ground contact but fully exposed to the weather the average life of 50 mm thick cypress heartwood is 15-25 years. This is similar to the durability that could be expected from timber treated to the H3.1 specification with light organic solvent preservatives (LOSP) although there is usually more variability in naturally durable timber than in treated radiata pine sapwood.
Horizontal, upward facing surfaces, end grain and joint areas where water can be trapped are most susceptible to decay. If the surfaces are only partly exposed to the weather, are vertical or steeply sloping, and not end grain, the chances of decay are relatively low and a much longer service life is likely. 100 x 100 mm verandah support posts on steel brackets and with the upper ends protected by an overhanging roof are likely to have a service life several times greater than that of fully exposed 50 mm thick material.
The building code specifies standards for slip resistance of pedestrian access routes. Surfaces which provide the direct access route (including where this is a deck) require a slip resistance of 0.4.
The Department of Building and Housing website has the basic information in a comprehensive format.
The Building Code compliance document D1 outlines the requirements for access routes, and states in Table 2 that timber is OK in dry level conditions, but needs an across-grain profile or sand/grit finish for wet and sloping zones.
Algal growth over time will require waterblasting as a maintenance scheme, as per subclause 4 of table 2.
Alternatively, unprofiled timber can be used with a fixed weatherproof coarse matting providing slip resistance of 0.4 for the main access route across the deck.
The Building code for slip resistance for pedestrian access routes states that surfaces which provide the direct access route (including where this is a deck) require a slip resistance of 0.4.
The Department of Building and Housing website has an overview regarding slip resistance
The Building Code compliance document D1 outlines the requirements for access routes, and states in Table 2 that timber is OK in dry level conditions, but needs an across-grain profile or sand/grit finish for wet and sloping zones. Algal growth over time would need waterblasting as a maintenance scheme, as per subclause 4 of table 2. Alternatively, unprofiled timber can be used with a fixed weatherproof coarse matting providing slip resistance of 0.4 for the main access route across the deck.
If your beam is going to be used in a situation where appearance is important such as house interiors, halls etc – appearance Grade A should be specified. This calls for a flush, filled and sanded surface.
Appearance Grade B is intended for applications where surface appearance is not so critical and a machine planed finish that may have occasional skips and other minor voids is acceptable.
Six Hazard classes are used to describe the service exposure conditions in relation to biological hazards that could cause degradation of wood. More information is available on the website
Are there special timber treatment requirements for NZ Radiata timber in tropical conditions, especially insect attack?
Use CCA treated timber for termite protection, H2 is for framing timber, H3 (not H3.2) for above ground exterior and H4 or H5 for ground contact.
Australian standards are usually applied with regards to dealing with termites in the Pacific Islands.
AS 1604.1 for sawn and round timber, AS/NZS 1604.2 – AS/NZS 1604.5 for reconstituted wood products, plywood, LVL and glue laminated products.
These standards would meet or exceed likely requirements in tropical areas where termites are a hazard.
Standards New Zealand: Timber Treatment –
These days most H1.2 treatments are with boron salts. These are very low toxicity preservatives and should pose few problems when used for indoor furniture, although it would be a good idea to ensure there is either a paint or other surface finish on the furniture so that there is no direct skin contact with the treatment.
H3.1 treatments are usually organic solvent treatments (eg. LOSP). These can cause some dermatitis-like problems when freshly treated timber is handled, particularly if a lot of residual solvent remains. They also have a fairly pungent aromatic smell which may take a while to dissipate from the treated timber. Again, painting of the timber would be recommended once all the solvent has evaporated.
H1.2 boron treatment would be the preferable option.
Untreated kiln dried pine should not be regarded as equivalent to H1.1 treated framing.
H1.1 timber specification covers additional protection against insect attack and H1.2 should be used if H1.1 timber is not available.
NZS 3602:2003 does specify a number of instances where kiln dried untreated framing can be used as an alternative to H1.1, but untreated wood should not be used unless specifically allowed.
The understanding is though, that the standards will be changing very soon, and kiln dried untreated timber will be excluded from most of the areas that it is currently permitted in.
It is also likely that the H1.1 specification will also be removed completely and that timber treated to the H1.2 specification will be the minimum requirement for almost all radiate pine framed houses.
More information on Wood Preservation and the Hazard classes
Also read What is a Hazard Class?
The piles are expected to be permanently below ground level after construction. Groundwater level is expected to be not far below the tops of the piles.
Wooden piles in this context should give a 100+ year service life. Untreated wood that is permanently below groundwater level will not decay so treated wood certainly won’t either.
The large size of the piles means that there is much more preservative chemical present than in the 50x50mm stakes on which decay resistance is normally evaluated. This means that the above-groundwater portion will have a longer life than is assigned to H5 timber which will be longer than H4 treated timber in the same situation.
An architect had an issue with raised grain on exterior facings. The facings had been used as part of an expensive reclad on a previously leaky home. While they were weathertight, the owner was unhappy with their appearance and demanded that the problem be rectified.
Raised grain is a machining fault caused by springback of compressed wood when its moisture content increases. The compression can be caused by blunt or improperly jointed planing knives.
To resolve it is best to leave the problem areas until after summer if possible, allowing the heat and summer humidity to allow full stress relief before sanding and then repainting.
Refer to the pages on Exterior Finishes on the NZ Wood website
Can Lawson cypress, lusitanica or macrocarpa be used for structural framing where H3.1 treatment is specified?
Locally grown Lawson cypress, lusitanica and macrocarpa has heartwood that is in Australasian durability Class 3 – i.e., in testing of ground contact 50 x 50 mm stakes it has been shown to have an average life of 5-15 years. The average life is towards the upper end of this range.
Note that the sapwood of all species is non-durable.
For macrocarpa and most lusitanica there is sufficient colour variation between sapwood and heartwood that they can be easily segregated but in the case of Lawson cypress, the pale colour of heartwood makes it difficult to differentiate between heartwood and sapwood in finished products. Pieces containing sapwood should be segregated out immediately after sawing if timber is to be used in external situations.
Away from ground contact but fully exposed to the weather, the average life of 50mm thick heartwood of these species is 15-25 years. This is similar to the durability that could be expected from radiata pine treated to the H3.1 specification with light organic solvent preservatives (LOSP).
In situations where it is protected from the weather a service life exceeding 50 years could be expected.
These heartwoods are resistant to preservative penetration and there is little to be gained by putting them through a preservative treatment process. The sapwood is not durable and variable penetration is likely when conventional vacuum-pressure and light organic solvent preservative (LOSP) processes are used for H3.2 and 3.1 specification treatments. It can be treated using boron preservatives to the H 1.2 specification.
The NZS 3602:2003 requirement for some specific applications (such as a “flat” roof is H 3.1) treated pine. Providing that the Lawson cypress, lusitanica or macrocarpa is heartwood, it should be a satisfactory substitute for H3.1 treated radiata pine.
However, if the timber contains significant amounts of sapwood it will not be equivalent to H 3.1 treated pine. While the sapwood could be treated to meet the H1.2 specification with boron it would not be an acceptable substitute for applications where H3.1 treated radiata pine is specified.
Of the eucalypts, the bluegum and stringy bark species are durable in ground contact so they will be more than sufficient for decking, therefore suitable varieties include saligna, botryoides, muelleriana, globoidea, eugenoides, microcorys and pilularis.
The eucalypts listed are a slightly higher durability class (Class 2-3) and therefore more reliable as decking.
There are both indigenous and exotic hardwoods grown in New Zealand.
Some of the indigenous species are of limited practical use for construction applications, and nearly all are in very limited commercial availability.
Indigenous hardwoods include:
Locally-grown exotic hardwoods include:
- Australian blackwood (Acacia)
- The Eucalypt family
- English elm
- European ash
- Black maire
- English oak
Under the NZ Building Code, cladding should comply with the minimum durability requirement of 15 years when maintained as specified. The serviceable life can be much longer and can exceed 50 years if coatings are properly maintained.
Under NZ Standards 3602 table 2 ref 2A.1 untreated macrocarpa “dressing heart” grade weatherboards are deemed to provide a 15 year durability performance and are therefore deemed to comply with the building code for weatherboards. As an example C. macrocarpa is ideal for weather boarding and framing but you need heartwood and look for clear boards if you can as it tends to check round green knots when exposed to sun while encased knots drop out. With an oil based stain clear weatherboards can prove to be very stable. C. macrocarpa is only class 3 durability so any areas that remain wet are susceptible to rot.
Note that Leyland cypresses, a hybrid of C. macrocarpa, should be even better for cladding than macrocarpa.
See Macrocarpa on the NZ Wood website
See Building Legislation and regulations on the website
Any softwood needs to be treated for use as decking except macrocarpa heartwood. Its natural durability can be sufficient for this purpose (although its durability is unreliable in moderate-high decay hazard situations, and occasional failures may occur within 10-15 years).
Most hardwood is naturally durable and resists all kinds of wear and tear. Locally grown eucalypts can be suitable for decking.
The Decking How-to-build guide suggests treated Radiata Pine.
The flooring should have been kiln dried. The idea of acclimatising is that kiln dried timber usually has drier and wetter pieces that will slowly adjust to whatever equilibrium moisture content is appropriate to the situation they are in.
For acclimatising ‘in situ’, the flooring is stacked with fillets (narrow strips of wood) between each layer. It will have been delivered block stacked, i.e. without fillets.
If the house is under construction then there is little point in doing that because the ambient conditions during construction will not be those when the house is complete and occupied, so some change is unavoidable as the flooring equilibrates to the final conditions.
If, however, the flooring is to be used for an extension to an existing house then there is merit in fillet stacking it for two or three weeks to “acclimatise” (or equilibrate) and this will keep any subsequent shrinkage to a minimum.
More on moisture measurement
More on the timber drying process (focuses on pine but is applicable to other species)
Wood: the most renewable of all building materials
- Growth and production of one tonne of wood absorbs a net 1.7 tonnes of CO2 from the atmosphere. (Based on the amount of carbon stored in the timber – making an allowance for all the energy used, and CO2 produced, in its growth, harvesting and processing.)
- One tonne of steel has added 1.2 tonnes of CO2 into the atmosphere.
- A typical steel house frame has added 4.5 tonnes of CO2 into the atmosphere – the equivalent to the emissions from driving 22,500 kms in an average car.
- A typical wooden house frame has absorbed 9.5 tonnes of CO2 from the atmosphere – the equivalent of 47,500 kms of driving in an average car.
- Timber frames mean years of CO2 “in the bank”
- Energy usage of a well-built, properly insulated home will be similar whether built with a steel or wooden frame (although steel frames will “leak” more heat than wooden frames if not properly insulated).
- The choice of wood or steel makes the difference between starting with either a healthy CO2 credit or deficit.
- An average house uses around 10,000 kWh of energy per year for heating and lighting, which represents CO2 emissions of 2.3 tonnes (based on electric power).
- Choosing a wooden house frame will provide over four “free” years of CO2 emissions.
- Using a steel frame is the same as adding an extra two year’s worth of average household CO2 emissions into the environment. Steel and timber: the afterlife
- Most construction timber is buried in a landfill at the end of its life. Up to 97 percent of the carbon in the wood is permanently stored under the ground – capturing CO2 released by fossil fuels and returning it back beneath the earth’s surface.
- At the end of the building’s service life, steel frames can be recycled for other uses. This requires significant processing energy, although this is a fraction of what was required to produce virgin steel.
Wood can take the heat
- When exposed to fire, wood retains its strength longer than steel.
- Average building fires reach temperatures of 700 to 1000°C.
- Steel weakens dramatically as its temperature climbs above 230°C, retaining only 10 percent of its strength at 750°C.
- Wood generally does not ignite until it reaches 250°C. Once it catches fire, wood develops a protective insulating char layer.
- After 30 minutes a large wooden beam will have lost around 25 percent of its strength in a 750°C fire and retain structural integrity – a steel beam will have lost 90 percent strength and will have failed.
- There is no such thing as a “fireproof” building. The contents of most buildings are combustible – and it is normally these rather than its structural components which pose the greatest fire hazard to life and property.
Can something like ChemWash be safely used to clean down cladding such as macrocarpa that is not stained or painted?
Yes. Chemwash materials will have no effect on the macrocarpa, even if it is not stained or painted. Chemwash materials affect living plant matter, not dead plant matter.
It is recommended that you DO NOT use treated timber to cook any food (including charcoal type BBQs or open/camp fires) as the chemicals used to treat the wood can be released whilst burning.
If you are unsure if the wood you have at home is treated or not, it is best not to use it.
Go the safe route and buy a cord of wood from your local firewood supplier (or talk to your local timber merchant to see if you can acquire some untreated offcuts).
For more information, view the ‘disposal of treated wood’ page.
Totara (Podocarpus totara)heartwood is in class 1 (very durable) of the Australasian wood durability classification system. The sapwood of all species is rated as class 4 (non-durable). Although the sapwood of totara has not been specifically tested, it is likely to be non-durable.
While there are anecdotal comments in old references that the sapwood of totara was durable enough for use as exterior woodwork in buildings and that it was resistant to attack by the common house borer, that was at a time when lead based paints were common.
Totara sapwood is probably satisfactory for use in low-moderate decay hazard situations where there is some added protection from decay, but it is unlikely to be durable enough for outdoor furniture if a minimum service life of ten years or more is required.
It all comes down to the Light Reflective Value (LRV) of the paint you are considering using.
The approximate light reflectance of a colour indicates the amount of visible light that a colour will reflect. Black has a LRV of 0% and absorbs all light. The surfaces are consequently very dark and can get very hot. In contrast, white has a LRV of 100% and keeps substrates light and cool. All colours fit within these two extremes.
Mid to dark colours are not suitable for some exterior substrates and if used may cause damage to the substrate, such as warping, checking and premature failure.
Resene CoolColour™ in some instances can be an option and for best results it is suggested that a white undercoat be used.
Always check with the substrate supplier prior to commencing any work to ensure the colour selections fit within their guidelines and these guidelines should be followed particularly if any substrate guarantees are involved.
The following links may be useful when making a decision:
It is best to consult a specialist in antique furniture. Look for furniture restoring specialists in the Yellow Pages.
While you could do it yourself, a specialist will be able to ascertain the best finish, and will have the most suitable tools for the job.
NZ Wood is a programme for the promotion of the wood industry and the use of wood.
If it is just mould or algae on the surface that is causing the discolouration you can use a 1:4 solution of household chlorine bleach and water, adding a teaspoon of dishwashing detergent per ten litres. It is important that the detergent does not have ammonia in it.
This is sprayed on and may require some light scrubbing to remove the mould. It needs to be rinsed with fresh water afterwards.
It is probably simpler to buy one of the proprietary products available from hardware outlets such as “deck scrub”, “30 seconds”, “wet and forget” or similar.