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The information supplied has been provided to assist with projects to help perform well over time. In cases refunds or return are not available after pick-up or delivery, as we can not monitor the environment the timber is in. Refunds do not have to be accepted for change of mind. Nationwide Timber is the supplier only and take no legal liability.
Select Grade AS 2796 – providing a floor where the feature present or natural discolouration will not dominate the appearance of the floor. Features that are permitted still include short narrow gum veins, a limited number and size of past borer activity and small tight knots.
Standard Grade AS 2796 – providing a floor that may have significantly more character than a Select Grade floor. To some degree this will depend on the features present in a particular species. In one species gum veins may naturally be prevalent while in another there may be few gum veins but past borer activity may be more prevalent. Therefore, this grade can be expected to have greater character than Select Grade, and contain an increased amount of gum vein, past borer activity, tight knots and natural discolouration.
Feature Grade AS2796 – providing for a floor that contains boards with similar features to Medium Feature – Standard Grade but where the length of features such as gum veins may be longer and past borer activity may be more frequent. Again depending on the species, features will vary and in some instances boards meeting high feature grade may only appear moderately featured.
Cover Grade – this grade contains more than the permissible number of natural features. Cover grade will contain miss-machining/manufacturing defaults, and can contain large amounts of gum vein, knot holes and other natural features such as holes.
Prestige Grade – is best referred to as a mixture of select and standard grade.
Rustic Grade – is best referred to as a mixture of feature grade and standard grade.
External decking timbers exposed to the weather will reach Equilibrium Moisture Content (EMC) with their surroundings after a period of 9-18 months, depending upon prevailing weather, size and type of timber used.
For coastal Australia, decks that are well ventilated should reach an EMC of approximately 16%. For decks close to and over water, EMC’s will normally be a little higher (18-21%) and for dry inland areas considerably lower (10-12%).
Depending on location and species, the amount of shrinkage occurring in unseasoned timber will vary. Generally, about 6% shrinkage (6 mm per 100 mm) should be expected for unseasoned hardwood. An indication of shrinkage rates for individual species is given in Technical Data Sheet 16, Species Properties and Uses. Allowance should therefore be made for shrinkage in unseasoned bearers, joists and decking, and for the gaps that will develop between the decking boards.
A minimum gap of 6 mm is recommended between decking boards to allow for good drainage and ventilation around boards. Unseasoned decking boards should be laid tight together, with subsequent shrinkage creating the required gaps.
As an example, if unseasoned spotted gum decking (45 x 120 mm) was butted together on installation, the final gap between the boards would be approximately 6% of 120 = 7-8 mm. Seasoned decking should be installed with the required 6 mm minimum gap at the time of laying. Closing of these gaps may occur during prolonged wet periods. Larger gaps may be necessary for areas of higher EMC e.g. over water.
Timber delivered to site should be stored supported on level bearers not less than 150 mm clear of the ground. Timber should be left block stacked and banded until required. Both seasoned and unseasoned decking should be covered to protect it from the sun and rain.
End-Plating and Sealing
All decking should be coated with either a suitable water based or oil on all four sides before installation. To reduce end splitting in unseasoned timber, the end grain should be coated immediately after sawing with a suitable sealer such as Petroleum Jelly or Mobilcer-M Wax Emulsion.
In addition, all unseasoned sections 300 x 75 mm or greater should be end-plated with a multi-toothed plate connector covering at least 50% of the exposed end section. Timber should be specified and supplied to site with the end-sealing and plating already in place.
All fixings (nails, bolts, screws, plates, etc.) should be either stainless steel, monel metal, hot dipped galvanised or mechanically plated.
Table 3 provides relevant fastener details for the fixing of the decks. Where CCA, ACQ or copper azole treated timber has been used and continual moisture is present, hot dipped galvanised bolts etc., should be coated with a heavy bodied grease, bitumuous epoxy paint or plastic sheath prior to installation.
Bolt holes in unseasoned timber should be drilled to a size equal to the bolt diameter + 10%. Where multiple bolts or fasteners are used in unseasoned timber, allowance for shrinkage should be made to avoid shrinkage restraint and possible splitting.
Pre-drilling for screws or nails may be necessary to avoid splitting. Where pre-drilling for screws or nails is required, the pre-drilled hole should be approximately 80% of the shank diameter of the screw or nail. The size of fastener required to fix the decking boards may dictate the minimum deck joist thickness. Table 6 provides guidance in this regard.
The design of the joints is a key factor in ensuring the durability of the structure. When designing joints in timber decks, the following general guidelines should be considered:
The performance of the decking and timber substructure can be markedly enhanced by ensuring adequate ventilation. Care should be taken to avoid dead air pockets. The wider the decking board spacing and the greater the ventilation, the longer the deck will last. As a minimum, a final decking board spacing of 6 mm is recommended. Not allowing adequate ventilation and air-flow will cause cupping of boards.