Coatings of steel structures
Paint Systems for Steel Structures
Paints for industrial use are gaining increasing attention nowadays, thanks to their quality and high durability, providing steel structures with long-term protection.
The selection of a paint system is influenced by a number of factors. The criteria are, of course, chosen according to who is making the selection. From the perspective of the person applying the paint, the decisive factors are application speed, the need for a small number of layers, or, for example, the use of a paint tolerant to poorer substrate preparation. On the other hand, for the investor, the main concerns are the price of the paint system, its service life, and easy maintenance. However, very important and often overlooked criteria are also legislative requirements, health protection of the person applying the paint, and also environmental protection.
Main Criteria for Selecting a Paint System
- Substrate – An important criterion for the correct choice of paint system is the surface of the material to be coated. This determines the method of surface preparation, the type of primer, and, last but not least, the total thickness of the paint system.
- Paint Application Method – Another criterion is the method of paint application. Whether it is possible to apply the paint manually (with a roller or brush) or if high-pressure spray equipment is required. Climatic and weather conditions also play an important role in the application, as not all types of paints can be applied under any circumstances.
- Drying – Here, time plays a major role. It depends on the temperature and humidity of the area designated for applying the protective coating. If part of the painting is done indoors and part on site, it is important to consider the time between individual coats.
An important influence on the correct choice of paint is also the corrosive environment and the required service life. The degree of corrosive aggressiveness of the environment is a key factor for effective and long-term anti-corrosion protection of the material’s surface and is divided into the following categories.
Degree of Corrosive Aggressiveness According to EN ISO 12944
| Category | Typical Outdoor Environment | Typical Indoor Environment | Zinc Corrosion Rate per Year |
|---|---|---|---|
| C1 – very low | heated buildings with clean atmosphere, e.g. heated halls, offices, | <0.1µm/a | |
| C2 – low | environments with low pollution, mostly rural areas. | unheated halls where condensation may occur, e.g. warehouses, sports halls. | 0.1 to 0.7µm/a |
| C3 – medium | urban and industrial environments, moderate pollution with sulfur dioxide, coastal areas with low salt exposure | production areas with high humidity and low air pollution, e.g. food production halls, laundries, breweries, dairies. | 0.7 to 2.1µm/a |
| C4 – high | industrial and coastal areas with low salt exposure | chemical plants, indoor swimming pools, shelters for small vessels above sea level. | 2.1 to 4.2µm/a |
| C5-I – very high (industrial) | industrial areas with high humidity and aggressive environment | buildings or spaces with almost constant condensation and heavy pollution. | 4.2 to 8.4µm/a |
| C5-M – very high (marine) | coastal or shoreline areas with salt exposure | buildings or spaces with almost constant condensation and heavy pollution. | >4.2 to 8.4µm/a |
Corrosion Protection Systems
- Paints – each manufacturer specifies the composition and type of paints for a given corrosive environment, including steel surface preparation
- Hot-dip galvanizing – used from corrosive environment C3
- Electro-galvanizing – used from corrosive environment C3, rarely for steel structures, more often for locksmith elements
Paint Service Life is Categorized into Four Groups
- Low L – up to 7 years
- Medium M – from 7 to 15 years
- High H – from 15 to 25 years
- Very High VH – over 25 years
Types of Paints
- Primers – SYNTHETIC
- Primers – POLYURETHANE
- Topcoats – SYNTHETIC
- Topcoats – POLYURETHANE
The type of paint system, layer, degree of corrosive environment, and other criteria affect the final price of the prefabricated hall itself. There are many aspects influencing the price of the project, but quality anti-corrosion protection provides the basis for the long service life of these buildings. By choosing the right type of paint system, we can save considerable resources on later maintenance.
The corrosive aggressiveness of the environment and the type of paint determine the final selection of a suitable paint. Each manufacturer has different technological procedures.
Fire-Resistant Paints
Fire-resistant paints protect steel structures to the required fire resistance from R15 (15 minutes) up to R90. Usually, it is advantageous to design structures for R30. Lower requirements can be solved by static calculation for resistance R15, exceptionally also for R30. Each manufacturer has a specially developed paint based on water-dilutable paints up to synthetic fire-resistant paints.
Paint Price
The price of painting steel structures of prefabricated halls is mainly influenced by the investor’s requirements. You can find a detailed price of the hall according to the visualization in the Price List of Halls.
Steel Substrate Preparation Grades According to ČSN ISO 8501-1:
| Designation | Description or Requirement |
|---|---|
| St 2 – thorough hand and mechanical cleaning | When inspected without magnification, there shall be no visible oil, grease, or dirt, including non-adherent mill scale, rust, paint, and foreign matter. |
| St 3 – very thorough hand and mechanical cleaning | Corresponds to grade St2, but cleaning must be much more thorough and the surface must have a metallic sheen characteristic of the substrate. |
| Fl – flame cleaning | When inspected without magnification, the surface must be free of mill scale, rust, paint, and foreign matter. All residues may only appear as a change in the color shade of the surface (shadows of various colors). |
| Sa3 – visually clean steel surface | When inspected without magnification, there shall be no visible oil, grease, dirt, mill scale, rust, paint residues, or foreign matter. The surface must have a uniform metallic appearance. |
| Sa2 – thorough blast cleaning | When inspected without magnification, there shall be no visible oil, grease, dirt, and almost no mill scale, rust, paint, or foreign matter. All remaining residues must be firmly adherent. |
| Sa1 – light blast cleaning | When inspected without magnification, there shall be no visible oil, grease, dirt, or non-adherent mill scale, rust, paint, or foreign matter. All remaining residues must be firmly adherent. |
| Sa 2½ – very thorough blast cleaning | When inspected without magnification, there shall be no visible oil, grease, dirt, mill scale, rust, paint residues, or foreign matter. All remaining traces of contamination must only appear as slight stains or streaks. |
* Preparation grades are usually defined in Europe according to ISO 8501-1, for overseas projects according to SSPC and/or NACE.