EWPAA Structural Plywood and LVL Design Manual - Engineered ...

● surface moulds● poor detailingDecay: Decay or rot is caused by fungi. Decay fungi can cause a significant loss in strength of timber.Decay or rot of timber will not occur unless conditions are favourable for the fungi. The four requiredconditions are: a suitable temperature range (5 to 500C), moisture content of the timber approximately19% or higher, the presence of oxygen, and a food source (eg. starches and sugars in the timber).Wood which is kept dry with a moisture content below 19% will not be subject to fungal attack.Occasional wetting during the construction phase or while in service, for example due to wind blown rain,will not usually require preservative treatment. However, if the plywood or LVL is frequently wetted orcannot dry out or be kept dry, then the plywood or LVL should be preservative treated to an appropriatelevel for the decay hazard and required service life. Note that in applications or locations where highrelative humidity is experienced for extended periods of time, moisture content of the timber may be highand preservative treatment required. FIGURE 15.1 (Error! Reference source not found.) shows timbermoisture content relative to temperature and humidity.Surface Moulds: Moulds are a type of fungi whose activities are mainly confined to the wood surface.When exposed to moisture, untreated or unprotected timber surfaces may develop surface moulds. Thesesurface moulds require the moisture content of the timber to be about 20 percent or greater and aremore prevalent in warm, humid conditions. Moulds are limited to the surface and can be cleaned off withbleaches or wood cleaners commercially available. Surface moulds have no significant effect onstructural performance.The surface mould becomes inactive when the timber dries out (below 20% moisture content), but willreactivate if the timber is not protected and becomes wet again. Surface moulds can be avoided bykeeping the plywood or LVL dry or alternatively surface finishing the plywood with a coating containingmouldicides or fungicides.Typical example of surface mouldDetailing: If it allows moisture to saturate or become trapped in or on timber will cause untreatedtimber to decay quickly and will considerably shorten the service life of the timber product. Good detailingincludes details that reduce or prevent the timber from and reduce moisture ingress through end grain.Where timber will get wet, good detailing should ensure moisture is shed rapidly and that the timber isable to dry out quickly. If moisture traps exist, preservative treatment to meet the intended service life willusually be required.16.10 Resistance to Insect AttackThe main insect destroyers of timber are termites and borers.Termites are not usually a problem with plywood and LVL provided the application does not involveground contact and good building practices have been implemented in the design and constructionstages. Ongoing inspection and maintenance is essential. Where a termite hazard exists, for example, inapplications involving ground contact structural plywood or LVL should be preservative treated to anappropriate level for the required service life.254