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Hi all, looking to build a deck near (1 mtr away) from a pool. I am considering Spotted Gum (SG) but have heard of horror stories (cupping, warping etc) if its near a pool. My next choice is ironbark(IB). Probably will go for 86 x 19 boards, but can get 120 x 19 in the SG. Timber will be kiln dried. Any advice would be helpful in choosing. Area will be 60 m2 with about 10m2 undercover.
I am absolutely no expert on decking, even though I have done it for a job. From my experience, timber can vary so much that regardless of the species you can get all sorts of issues. sometimes it is limited to a few boards that want to cup other times it can be whole packs that end up twisting. I actually think you can't go wrong with Merbau (Kwila), but that isn't the same colour.
In short, make sure that the work you can't see (joists) are 100% solid and that the fixings you use are quality, and it gets a good sealing.
I put pine down for one reason, hardwood can split when it ages and injure bare feet. I don't know if it is a valid reason but bare feet and splinters don't seem like a good idea to me. I have synthetic decking in other areas and the one reason I did not use that was the high surface temperature it gets to but it is the easiest to lay, does not twist and warp and altogether way less problems that timber. Use all stainless fasteners, I always screw decks down with phillips head stainless screws.
Any timber can cup and warp, though its got not much at all to do with being near a pool. The actual issue is sunlight on green timber: the exposed side dries faster then the underside, causing it to shrink while the bottom doesnt. Straight up recipe for disaster every time. You have correctly identified the solution which is to ensure the timber is dry (kiln or well seasoned makes little difference so long as it's dry).
Given a choice of Spotty or Ironbark I'd go with the Ironbark: its more durable then Spotty by a fair margin. As Emit points out you need to pay attention to your joists also - its no good screwing down a good Class 1 durability hardwood into a piece of snot treated pine or other less durable species. A reeded underside on the decking also helps in that it allows the area between decking and joist to dry out which will give maximum service life.
We built a small bridge over a Council Pool with Merbau used for treads. A beautiful timber, but way back when and before we knew, the amount of tannins leeching out was astounding . Needless to say, the concourse was stained beyond repair and we received a giant broadside for that one!
Whatever is used make sure it is sealed allround with say Aquadeck or similar.
Also there is a rubber strip with turned down edges available to place on top of the joists. Given the situation(near a pool) that would be a good option.
As per John's advice, I'd go the Ironbark.