Timber Species Properties Relevant to Decks.
As you've probably already read, Yonnee got a bit upset in another
thread regarding timber durability issues relating to decking.
I know the feeling. There's really no substitute for properly
researching timber properties thoroughly before embarking on
exterior timber work. So I thought I'd post some further info for
all the DIY deck builders/owners out there...
Here's a useful (essential?) resource for self-education...
http://www.timber.org.au/resources/Revised%20P1.pdf
The above document has a reasonably comprehensive table that
lists the properties of various species. The rest of the document also
describes what the properties really mean (i.e: the fine-print).
However, as I said in the other thread, there's some devil in the detail
because the above-ground durability classes assume a "well-drained"
situation, but decking (and joist tops) can remain damp for
surprisingly long periods - so it's best to rely on the in-ground
durability class.
For in-ground durability class-1 timbers, reeding on the underside is a
nice extra but not absolutely essential. If you can't get reeding, give the
underside a coat of preservative before laying. To protect joist tops more,
fold alcor flashing along the tops (or that specially moulded
protector plastic that comes in a roll). Also apply preservative to
places where timber meets timber, especially where timber rests on timber,
since that's where moisture could be retained unseen for a long time.
For people in bushfire-prone areas, there's some extra things to know:
Currently, the only timbers rated as sufficiently fire-retarding to
meet AS3959 are Blackbutt, Kwila(Merbau), Red Ironbark,
River Red Gum, Silvertop Ash, Spotted Gum, Turpentine.
But of these, only Red Ironbark and Turpentine are in-ground class-1.
Blackbutt, River Red Gum, Spotted Gum are class-2, and Kwila(Merbau)
is class-3. These are all termite-resistant. Silvertop Ash is also rated
class-3, but is not resistant to termites.
[Actually, the table says Kwila(Merbau) is in-ground class-2 and
above-ground class-3, which sounds like it's the wrong way around.
You'd expect it to be less durable in-ground. Maybe that's a typo. But in
any case, one should be guided by the worst figure quoted - to be on
the safe side.]
Turpentine, although extremely durable, is a temperamental timber to
work with outside in applications where ongoing good appearance matters.
This is due to its high tangential shrinkage and occurence of a discoloured
dark brown heartwood as well as the other beautiful pinkish heartwood
(I speak from personal experience on this). So if you're trying to choose
between turpentine and red ironbark, go for the latter.
Happy reading. :)
