 | Special paints and finishes: Protect your investment
 | Caroline Côté, LEED® AP
Architectural Solutions Advisor
Email
To learn more about Caroline Côté |
In this article:
Many types of finishes can be applied to structural steel members. Standard primers, for example, provide adequate protection in essentially non-corrosive environments.
To learn more about the primer used by Canam Canada, see the article Paints in the November 2007 issue of Canam Info-Tech. It is important to note that, since October 2008, Canam only offers grey primer which has a 55% recycled content.
Choosing a coating system
Architects often choose to leave the interior or exterior of a building exposed. The use for which a building or part of it is intended can significantly influence the coating system required to provide the desired visual effect and ensure adequate coverage.
Once installed, structural steel components can remain exposed to various conditions, including:
- a temperate indoor environment, which requires minimal protection;
- a more aggressive indoor environment with prolonged exposure to a corrosive atmosphere, such as one exposed to a swimming pool or chemicals, which requires the application of a sophisticated painting or galvanizing system;
- an outdoor environment, which requires extra protection.
The designer must select the coating system best suited to the building's intended use and specify it on the drawings and in the specs. Product fact sheets, which include recommended surface preparation and application procedures, are available from all paint manufacturers (www.cdnpaint.org) and galvanization companies (www.galvanizeit.org). To ensure maximum effectiveness in multi-coat systems, it is important to follow the manufacturer’s recommendations, especially with respect to the compatibility of each coating.
Surface preparation
Surface preparation is essential to achieving optimal performance and durability. It is important to clean the steel surface by first eliminating any traces of dirt, oil, grease, mill scale or rust that could compromise adherence of the protective coating. The types of preparation and their descriptions are listed below.
| Preparation | Type | Description |
| SSPC-SP 1 | Solvent Cleaning | Removal of all visible oil, grease, dirt, soil, salt and other soluble contaminants by the use of solvents. |
| | |
| SSPC-SP 2 | Hand Tool Cleaning | Removal of loose rust, mill scale, coating and other loose foreign matter by the use of hand tools. |
| | |
| SSPC-SP 3 | Power Tool Cleaning | Removal of loose rust, mill scale, coating and other loose foreign matter by the use of power-assisted hand tools. |
| | |
| SSPC-SP 5 | White Metal Blast Cleaning | Removal of all visible oil, grease, dust, dirt, mill scale, rust, coating and other foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. |
| | |
| SSPC-SP 6 | Commercial Blast Cleaning | Removal of all visible oil, grease, dust, dirt, mill scale, rust, coating and other foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. At least two-thirds of each square inch of commercial blast cleaned surface shall be free of all visible foreign matter. |
| | |
| SSPC-SP 7 | Brush-Off Blast Cleaning | Removal of all visible oil, grease, dust, dirt, mill scale, rust, coating and other foreign matter, except for tightly adherent foreign matter. The brush-off blast cleaned surface should provide good adhesion and bonding of coating. |
| | |
| SSPC-SP 10 | Near-White Blast Cleaning | Removal of all visible oil, grease, dust, dirt, mill scale, rust, coating and other foreign matter, until at least 95% of each square inch of the near-white metal blast cleaned surface is free of all visible foreign matter. |
| | |
| SSPC-SP 11 | Power Tool Cleaning to Bare Metal | Removal of loosely adherent rust, mill scale, coating and other loosely adherent foreign matter, until at least 95% of each square inch of the bare metal surface is free of all visible foreign matter. |
| | |
Table 1: Surface preparation
Reference: Surface Preparation Specifications (SSPC, Steel Structures Painting Council)
To provide a smooth finish to highly visible elements, other preparation steps may be taken as referred to in the Architecturally Exposed Structural Steel (AESS) specifications.
Sealed welds
In the case of structural steel elements exposed to harsh weather and corrosive or humid environments, it is strongly recommended to seal the welds before application of special coating systems or hot dip galvanizing. When galvanizing, the acid used for cleaning the steel can penetrate between the welded steel parts and eventually seep through the protective zinc. It should be noted that, since hot dip galvanizing is performed by dipping, the size of the steel sections must not exceed the size of the tanks.
Even though sealing welds involves additional time and costs, it prevents potential problems such as rusting or staining. In environments requiring strict hygiene, as in a food processing plant, it is essential that the designer specify sealed welds.
Photo courtesy of Justin Viens architecte
Figure 1: Galvanized steel joists with sealed welds
In an environment with a high relative humidity, such as one exposed to a swimming pool, humidity can seep into the gaps between welded steel parts. Applying paint systems with a spray gun does not ensure coverage in inaccessible areas. Sealing welds eliminates gaps that are difficult to access and minimizes the occurrence of stains or spots on the architectural elements.
Figure 2: Special paint application on sections with sealed welds
Accessories
To optimize the quality of the end product, the fasteners (screws, nails or bolts) chosen for the structural members must have the same performance properties as the finish selected. Any surfaces damaged during on-site installation must be touched up to ensure ongoing protection.
Since the use of sophisticated coating systems involves a substantial investment, it is preferable to take all the necessary measures to prolong the life and maintenance cycles of the structural elements.
Information
For more information, please contact our experts:
Our projects
Consult the list of projects completed by Canam Canada.
|
| |
| Contact us
Feel free to send us your questions or comments regarding the InfoTech Express.
Technical questions? Consult our experts:
| |
|
| |
| |