Hardwood Vs Softwood Essay
This research report will take an in depth look at the use of hardwoods, and softwoods in the manufacture of outdoor furniture. This brief target audience is technology studies students, teachers, and will specifically investigate safety aspects, structure types and availability, adhesive properties, environment issues, and durability. The hardwoods considered in this report include Jarrah, Spotted Gum, and Tasmanian Oak.The softwoods considered are Radiata, Calantis and Hoop Pine.
Hardwood is timber that has a particular type of interlocking cellular structure. The trees have broad leaves and are made up of thousands of different species. Generally Australian hardwoods used for the manufacture of outdoor furniture consist of various eucalyptus species but mainly include timbers such as Jarah (South Western Australia), Spotted Gum, and to a lesser degree Tasmanian Oak. All of these timbers are relatively harmless although the dust if swallowed, may cause abnormal conditions. The usual first aid is to drink water, and if there is abnormal discomfort, seek medical attention. Eye contact with dust may be irritant, and cause redness and watering. To be safe wear glasses to protect eys. If eye contact occurs, it is recommended to flush thoroughly with water for at least 15 minutes and if irritation persists seek medical attention. Inhaling the dust of Tasmanian Oak can cause some reparatory problem. Inhalation of dust of hardwood may be irritating to nose, throat and lungs. If this occurs leave the dusty area, or apply a mask. Hardwood dust can also be a fire/explosion hazard, so avoid sparks, the build up of static electricity, and sources of ignition in all electrical equipment and dust extraction equipment. In a fire, use water jets to extinguish flames.
Swallowing of softwood dust may cause abnormal discomfort but usually presents less problems than the three hardwoods mentioned above. Again the treatment consist of drinking water and if there is further discomfort seek medical attention. If eye contact occurs, irritation as well as redness and watering may happen so it is recommended to wear glasses while working. If dust from softwood is inhaled, irritation to the nose, lungs, and throat is possible but not common. A dust mask is always recommended when wood dust is present. Softwood should be stored in a well-ventilated area away from heat, flame, and sparks. Dust from softwood can form an explosive mixture with air, so keep away from sources of ignition.
Timber when viewed under a microscope has two main structures. Hardwoods typically characterised by large, tubelike vessels or pores. Hardwood does not necessarily mean it is hard as one of the softest timbers , balsa wood is a hardwood. The tubelike vessels in hardwood are intertwined making the timber much stronger in relation to is weight compared to softwoods. Some of the well know hardwoods are eucalypts, oaks, ashes, red cedars, and hickory. Jarrah, Spotted Gum and Tasmanian are commonly available across Australia although Outdoor Furniture manufacturers corner the market with Jarrah supplies. Spotted gum and Tasmanian Oak are readily purchased from local Yeppoon Hardwares.
Softwoods or non-pored woods have a simpler and more uniform cell structure than hardwoods and under a microscope present similar to brick work.. This is due to the fact that softwood is bulkily made up of long, thin cells called tracheids.. These cells provide mechanical support but it should be noted that softwoods generally have much less strength in relation to their weight when compared to hardwoods. Some types of softwoods include western red cedar, cypress, and radiata pine and can usually be purchased at local hardwares.
The use of an increasing number of natural hardwoods by the timber industries has revealed that some timber characteristics, such as high density and high level of extractives (waxes, oils and resins), make them difficult to glue. It is essential to realise that different adhesives should be used for various applications. Selection of adhesive should be made on the basis of the type of components, species, wood grain direction and service conditions. It is a recommendation that gluing should be carried out immediately after machining. From research, it shows that epoxy resin is an unsatisfactory adhesive to use on hardwood, but depends on species. Spotted gum is particularly difficult to glue or finish because of its extractives and needs lengthy seasoning to overcome this problem. For this reason much of the outdoor furniture make from hardwoods are simply screwed together eliminating joints and glue.
The generally porous nature of softwoods and their minimal extractives make them particularly suited to modern gluing techniques. Their very low density, allows the glue to penetrate open cellular timber structure. It is essential that different adhesives are specifically researched for set applications depending on the weather exposure and strength requirements.. From research, most adhesives are satisfactory for softwood, and most commonly include polyvinyl acetate, high strength wood glue and epoxy resin.
One of the major environmental issues of using hardwood is the question of sustainability. Can harvesting trees be done indefinitely? If not, then at some stage it will have to stop and the cost of following resource depletion and environmental degradation to the end is the same as for any biological population that outgrows and poisons its habitat. Most hardwood timbers use in building come from old growth native forest. The average tree reaches an average age of 25 – 40 years before it is felled to be milled. Currently hardwood timber is being depleted because it is being used faster than it can be replaced. The larger environmental issue with timber conversion is two fold. Firstly carbon dioxide in the atmosphere is creating a warming blanket around the earth gradually increasing the overall temperature. The diagram below clearly shows that timbers adds 30 kilograms of carbon into the atmosphere with every ton of timber sawn. This is relatively small however when compare to the production of steel or aluminium. However it seems essential in the long term that trees are grown faster than they are cut down.
THE GREEN HOUSE EFFECT ENERGY burned and carbon released for construction materials (Buchanan, A. H. 1990)
Fossil fuel EnergyCarbon releasedCarbon stored
Rough Sawn Timber1.58503015250
Aluminum 4351,100,000 8,70022,0000
Softwood differs from Hardwood in that is mainly is produced from plantations and is grown in a more sustainable fashion. A typical softwood tree reaches harvesting age between 10 – 30 years which is much quicker than old growth forest hardwood timber.The carbon released from milling softwood is similar to hardwood so still contributes to the green house effect, but at least in softwood plantations carbon is still being locked up in the form of timber. When hardwood is milled generally it is never replaced so the carbon that is released never gets extracted by new growing trees such as in plantation softwood.
Durability is defined as the length of time a material will last in relation to weather, decay and general wear. The hardwoods investigated in this report all offer superior durability to softwoods in that they are all much stronger proportionally to their weights. Spotted gum and Jarrah are particularly hard wearing and very weather resistant even without finishing. Tasmanian Oak is softer and more prone to rotting and fungal attack.
All of these timbers will crack and warp if left unfinished as the moisture moving in and out of the wood eventually degrades the cellular walls.
Softwood in exposed situations offer very limited durability. Most species are very prone to decay, warping, splitting and this combined with their softness makes them not really suited to any outdoor application. This has been overcome in recent years by treating pine with Chromium Arsenate a timber preservative which is placed in the timber under high pressure. Treated pine is guaranteed to last in the weather approximately 40 years. This treatment however does leave the timber with a distinctive green colouring restricting the design aesthetic options.
This report has investigated, safety aspects, structural types and availability, adhesive properties, environmental issues, and durability. The intent of the report is to clearly outline the best alternative when choosing timber of the manufacture of outdoor furniture. The comparative table below shows the strengths and weaknesses of the two timber types.
COMPARATIVE TABLE – SELECTED HARDWOODS VERSES SELECTED SOFTWOODS
More hazardous than softwoodMuch strongerAll available at local hardware’sGlues poorly. Oily extractives provide low adhesion Less friendly than softwoods as it take much longer to replace and isn’t readily grown in plantationsVery weather resistant and hard resisting denting and physical damage
Less hazardous then hardwoodGenerally offers half the strengthAll available at local hardware’sHigh – glues readily with very high strengthMore friendly than hardwood as it is grown in plantationsNot weather resistant. Soft, Prone to fungal attack and decay.
It is clear from the comparative table that hardwood is far more superior for outdoor furniture manufacture. Although it is less environmentally friendly to use hardwood it does offer the durability and much superior strength required in this type of application. As far as safety is concerned, dust is the most significant hazard and in both timber this is easily overcome with some sensible protective equipment such as a dust mask or respirator.
5. And personal knowledge.