This is a significant emerging issue for houses built in the mid 1990's in South East Queensland.
In order to provide a reasonable design life structural elements must be maintained and or protected to achieve the nominal 50 years proscribed for domestic house built in Australia.
Unfortunately the coating protection system, specified by the design engineer/BSA licensed home designer, or selected by the Builder or passed by the Private Building certifier / local council inspector was not compliant for the posts with exterior exposure conditions. The relevant Australian standard prescribes various coating systems. Hot dip galvanizing would be the preferred durable treatment with up to 25 years without maintenance.
In the attached image the corrosion system applied is the default zinc based primer. This coating is not recommended for exposed locations. It would appear even 5-10 years of protection would be hopeful. Here obviously the protection system has been completely negated with surface corrosion well advancing.
We recommend that all corroding steel posts be exposed with some concrete removal at the surface level for careful inspection to determine how far the corrosion has progressed. If the wall has reduced to less than 3mm from an original 4mm thick wall (75x4mm SHS is a very commonly used post size for house bearer support) further capacity checking may be needed or post replacement may be suitable.
If the corrosion is not too severe new protection preparations, coatings and encasement details should be applied to extend the post design life back towards the intent of the Australian design standards.
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