igh 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.SOFTWOOD 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.HARDWOODOne 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...
