When building in a marine environment there are a number of aspects required by the Building Code of Australia (BCA) to be considered. If the appropriate products are not used, premature failure can occur with undesirable results for the builder and client.
In general, the BCA uses the terms distance from breaking surf and distance from salt water not subject to breaking surf to determine the necessary level and type of protective coating required on various metal building products to be used in a marine environment. However depending on the building product being used, there are specific definitions that apply. Therefore it is important to check the standards for metal components if you are building within 1km of the coastline.
The products nominated by the BCA include:
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a) Metal Roofing
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The High Category is defined as the building being 200 metres from breaking surf where the Zincalume coating needs to be AZ150 (grams cover per sq.m) with or without an organic paint finish.
If the building is 50m from a sheltered bay the Zincalume coating needs to increase to AZ200 with or without an organic paint finish.
The Very High Category is defined as buildings between 100 and 200 metres from breaking surf. In this environment a purely Zincalume coating in not suitable, only an organic paint finish on top of Zincalume AZ200 is suitable.
Check with your roofing material manufacturer to ensure that the right coating and finish is being used for the application as this affects compliance and warranties.
b) Structural Steel Work
The Moderate Category is defined as the building being more than 1 km from breaking surf or 100 metres from salt water that is not subject to breaking surf.
The required coating on external structural steelwork includes:
- Option 1 - 2 coats of alkyd primer
- Option 2 - 2 coats of alkyd gloss
- Option 3 - Hot dipped galvanise to a minimum of 300 grams per square metre
- Option 4 - Hot dipped galvanise to a minimum of 100 grams per square metre plus 1 coat of solvent based vinyl primer or 1 coat of vinyl gloss or alkyd
The Severe Category is defined as the building being within 1 km from breaking surf or within 100 metres from salt water that is not subject to breaking surf.
The required coatings on internal steelwork include:
- Option 1 - 2 coats of alkyd primer
- Option 2 - 2 coats of alkyd gloss
The required coatings on external steelwork include:
- Option 1 - Inorganic zinc primer plus 2 coats of vinyl gloss finishing coats
- Option 2 - Hot dipped galvanise to a minimum of 300 grams per square metre
- Option 3 - Hot dipped galvanise to a minimum of 100 grams per square metre plus 2 coats of solvent based vinyl primer or 2 coats vinyl gloss or alkyd.
It is important that nuts, bolts and associated brackets for the structural steel work have a similar level of corrosion resistance and are compatible so they maintain the integrity of the system. There is nothing worse than seeing rust marks scaring the finish for the reasons just stated.
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c) Wall Ties for Masonry
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On left, an example of where wall ties have failed due to corrosion causing brickwork to collapse.
Exposure Condition Area
- less than 1km from breaking surf or less than 100 metres from salt water that is not subject to breaking surf.
• Minimum corrosion protection required – Grade 316 or 316L stainless steel or an engineered polymer.
Exposure Condition Area – between 1km and less than 10kms from breaking surf or 100m to 1km from salt water that is not subject to breaking surf.
- Minimum corrosion protection required – sheet steel ties galvanised after manufacture – 470 grams per square metre on each side or galvanised wire ties – 470 grams per square metre coating mass.
All other areas
- Ties manufactured from galvanised sheet steel – Z600 or sheet steel ties galvanised after manufacture – 300 grams per square metre on each side.
It is critical that all nails and screws for use with wall ties and any other associated fixings have a similar level of corrosion resistance and are compatible so they maintain the integrity of the system and don’t become the weak link.
NOTE: The corrosion protection of built-in structural steel members requirements of the BCA have NOT been covered in this information sheet.
DISCLAIMER – the above is intended to provide general information in summary form. The contents do not constitute specific advice and should not be relied upon as such. Formal specific advice should be sought by members with respect to particular matters before taking action.