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Solar exposure and Shading
Do E values increase or decrease as the P/H values increase?

Woodsolutions Answer +

Wood is naturally slightly acidic with an average pH between 3 and 5.5. If the pH of the environment substantially changes, strength properties can be reduced. However, we are not aware that exposure to sunlight causes significant acidity in wood. There is some evidence that very high temperatures (eg. in an autoclave) cause a rise in acidity - see this paper: Such high temperatures are not likely to be found under natural conditions.


I am building a deck in a BAL19 rated area in Qld and wondering if the decking boards can be spaced at a tradition 3mm? Or is there a Qld specific requirement to have them spaced at 10mm in BAL19?

Woodsolutions Answer +

National Construction Code (NCC) requirements are satisfied if a deck associated with a Class 1 building is constructed in accordance with AS 3959. There is no Queensland variation to the NCC with regard to the spacing of decking, and AS 3959 does not impose any limitations on spacing. AS 3959 does contain the following Commentary: "Spaced decking is nominally spaced at 3mm (in accordance with standard industry practice): however, due to the nature of timber decking with seasonal changes in moisture content, that spacing may range from 0mm - 5mm during service. It should be noted that recent research studies have shown that gaps at 5mm spacing afford opportunity for embers to become lodged in between timbers, which may contribute to a fire. Larger gap spacing of 10mm may preclude this from happening but such a spacing regime may not be practical for a timber deck". Statements designated as Commentary are for information only and do not need to be followed in order to comply with the Standard.

Decking spacing

Joint sealant and joist to decking board protection. 1). For the frame (Joists, Bearers and steel posts) what material should I use for sealing interfacing elements? I intend to use an oil based treatment. I was going to use Ormonoid's "Duraseal Putty" but Feast Watson was not able to confirm its compatibility with their "Traditional timber oil natural" nor recommend a suitable sealant.
2). For the tops of the joists I intended to use a "malthoid dampcourse" prior to fitting decking boards. Once again they could not confirm either way if it would interfere with the effectiveness of their product at maintenance re coatings. n.b. I will be using Feast Watson "Matt look deck" for decking boards plus "ultra grip" on the top surface to achieve a P4 slip rating.
Your advice please on best practice treatments for these two applications.

Woodsolutions Answer +

We are not familiar with Duraseal Putty, but it sounds like a suitable end-grain seal judging by the description on the net. A more commonly used product is wax emulsion, click here for more information: Neither Duraseal Putty nor wax emulsion will be compatible with an oil finish, ie. the wax will repel the oil. However, this may not matter if the wax is applied only to the end-grain and/or interface surfaces. Malthoid dampcourse and similar products applied to the tops of the joists won't interfere with the decking but care needs to be taken to ensure that water can't get under the dampcourse material. There are special products for protecting the top edge of deck joists, eg. G-Tape which adheres to the joist, more info here:

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