The main issues are:
- Colour – fading, discolouration, ultraviolet effects, mould growth
New Zealand grown species that could be considered are:
- Radiata. Must be treated to H3 or H4. CCA is the only commonly available treatment that will achieve sufficient durability. An alternative to CCA would be ACQ or Cu-azole treatment but may be hard to find. (Timber treatment companies such as Osmose or Arch should be able to advise on availability.)
- Macrocarpa. Does not need treating, otherwise similar to radiata. Note: macrocarpa can be unreliable where it is fully exposed to the weather, i.e., a few pieces are likely to fail or need replacement within the 15-year minimum durability requirement.
- Eucalypts. These are mostly durable hardwoods. The Eastern Blue Gum group: (E saligna and E. botryoides) and the Stringybark group: (E. muelleriana, E. globoidea, E. eugenoides, E. microcorys, E. pilularis) are most suitable for decking.
- The heartwood of all the blue gum and stringybark species are durable in ground contact, lasting 15 to 25 years in ground contact and up to 40 years out of ground contact, giving an equivalent durability of H3.2.
Permanently shaded areas will become slippery so regular maintenance (waterblasting) is needed. Decking is usually grooved to reduce slipperiness. A surface coating of high built glassfibre-reinforced epoxy coating will overcome most of these problems. Screw fixing may be preferable to nail fixing although decking nails are resistant to popping. All timber is porous so will allow mould to penetrate and cause discolouration.
Wall linings for indoor pools
Durability is less of an issue with indoor pool wall linings. There is no danger to the wood from chlorinated water. It does not damage the wood and acts as a mild preservative. There will be discolouration though, as with any wood if it gets splashed.
Commonly available timber options would include pinus radiata, Douglas fir and macrocarpa. New Zealand-grown eucalypts could also be considered, or indigenous timber such as beech where a high end finish is desired.