The following provides guidelines for preparing an appropriate specification for painting galvanizing.
Specific projects may need to encompass additional requirements not included in this generalised specification and Section 10 of AS 2312.1 provides additional advice.
NOTE: For powder coating, while the general specification format would be appropriate, the technical requirements, notably surface preparation and application and cure conditions will be considerably different and need to be consistent with the guidelines of the specific powder coating manufacturer or the Australasian Institute of Surface Finishing (www.aisf.org.au).
This Specification defines the technical requirements for surface preparation and application of protective coatings that have been hot-dip galvanized in accordance with AS/NZS 4680. It does not cover powder coatings, which requires specific recommendations regarding surface preparation and coating system selection, application and cure.
(Accurately describe the article’s final location and scope of items to be painted.)
1.2 Definitions/Glossary of Terms
For a glossary of paint and painting terms, refer to AS 2310(18).
2. Reference documents
The following documents have been referred to in this Specification:
AS 1627 – Metal finishing – Preparation and pre-treatment of steel surfaces
AS 1627.1 – Part 1: Removal of oil, grease and related contamination
AS 1627.4 – Part 4: Abrasive blast cleaning (Note: Relevant for Service Requirements 2 to 6)
AS 3894 – Site testing of protective coatings
AS/NZS 2310 – Glossary of paint & painting terms
AS/NZS 2311 – Guide to the painting of buildings
(Note: Only relevant for Service Requirement 1)
AS 2312.1 – Guide to the protection of iron and steel against exterior atmospheric corrosion – Part 1: Paint coatings
AS/NZS 2312.2 – Guide to the protection of iron and steel against exterior atmospheric corrosion – Part 2: Hot dip galvanizing
AS/NZS 4680 – Hot-dip galvanized (zinc) coatings on fabricated articles
3. Technical requirements – coatings
(i) Surface preparation treatments, inspection and testing and health and safety shall comply with statutory requirements and the guidelines of AS/NZS 2311 or AS 2312.1 and AS/NZS 2312.2, as appropriate.
(ii) All cutting, welding and other physical working of the metal shall be completed before surface preparation and these shall be completed off-site, except for repairs made necessary because of damage during transport, storage and construction.
(iii) All paint forming part of the one paint system shall be from the same paint manufacturer.
(iv) No paint shall be used after the expiration of its shelf life or its pot life and all paint shall be mixed, thinned as appropriate and applied in strict accordance with the manufacturer’s written instructions.
(v) Apply the first (prime) coat to the clean, dry surface as soon as practicable after it has been prepared for coating.
(vi) Coating application shall only proceed when the surface temperature is greater than 15°C and at least 3°C above the dew point of the surrounding air.
(vii) Coating application procedures and the time elapsed between coats shall be consistent with this specification and strictly in accordance with the manufacturer’s written recommendations.
(viii) Where repairs to the coated finish are necessary and permitted by the Project Manager, they shall be carried out using the system approved by the manufacturer(s) of the original system, and to a standard which will not compromise the protective performance of the overall coating system.
(ix) The Project Manager reserves the right to check each and every stage of the coating process to determine the cleanliness of surfaces, degree of cure, adhesion, time between application and coating thickness, colour gloss and finish. When tested in accordance with AS 3894.3 each coat and the total coating thickness shall be not less than the specified minimum.
(x) After the completion of all painting works, all equipment and materials used in painting activities and all paint debris shall be removed from the site, which shall be restored to its original condition.
3.2 Surface Preparation
(i) Remove any oil, grease or wax in accordance with the relevant method described in AS 1627.1(19).
(ii) Remove all dirt, dust, water-soluble salts and other contaminants by appropriate methods consistent with the requirements of AS 1627.
(iii) Remove or smooth out all sharp edges, dags, weld spatter and laminations in a manner that such physical imperfections in the galvanized surface shall not thwart the even build-up of the subsequent paint system.
(iv) (Service Requirements 3 to 6 only). Lightly (brush or whip) blast all galvanized steel using a soft abrasive, such as limestone or aluminium magnesium silicate in a manner that profiles the surface without removing a significant amount of zinc from the surface.
(i) The first coat of paint shall be applied to the clean, dry prepared surface as soon as practicable after it has been prepared for coating and at least within 4 hours. Immediately prior to coating, the surface shall be air blasted or dusted off to remove any surface dust.
(ii) For Corrosivity Zones C5 and CX, or where otherwise nominated by the Project Manager, all edges and corners shall be first stripe coated with prime coat, prior to application of one full prime coat.
(iii) The prime coat shall be …………
[Add details for the primer/first coat from the paint system selected]
(Detail at least product name and minimum dry film thickness)
(iv) As soon as practicable after the minimum recoat time for the primer, apply …………
[Add details for the intermediate or top coat from the paint system selected. If there is an intermediate coat, add another step for the top coat]
(Detail at least the product name, the minimum dry film thickness for each coat to be applied and the minimum total dry film thickness of the paint system and colour/ gloss of final finish)
The final finish shall be smooth and uniform in colour and gloss consistent with best industry practice for the products specified.
(v) Damage or other defects in the coating system shall be feathered back to a smooth transition and patch repaired with the same products to not less than the specified dry film thickness.
Note: A editable version of this duplex coating specification is available from the GAA (email@example.com)