Blasting and Painting
Stainless Restoration's Blasting and Painting division specialises in abrasive blast cleaning and the application of protective coatings. Our primary focus is on the application of protective coating systems that provide excellent corrosion control at the best value.
All coating applications are monitored on site and many tests are performed which are necessary to ensure the long term performance of the coating. This includes on site monitoring of climatic conditions, surface preparation, application of the coatings, wet film and dry film measurement.
- Structures/Products for marine environments
- Steel Structures
Services we offer:
- Specification development
- Coating system selection
- Specification review
- Technical support
- NACE qualified inspectors
Stainless Restoration have facilities to shot blast and coat large, heavy duty applications/items. The company has fully enclosed facilities for both shot blasting and coating. The size of these facilities are 15m long x 5.5m wide x 5m high. All coatings are applied in a stand alone, fully enclosed spray booth, which contains a heating mechanism thus allowing the correct climatic conditions to be present before, during and after the coating process. This is essential in order to produce high quality, reliable coatings.
The Coating Process
In order to achieve a quality, reliable and long lasting coating Stainless Restoration follow good coating practices in line with recognised national and international standards.
In short, the surface is prepared by abrasive blasting, which creates a surface profile which acts as an anchor for the coating. Surface preparation is to a coating system what a foundation is to a building. If a coating system has a poor foundation (Surface preparation) it will fail sooner than expected which can lead to great financial losses. Furthermore, any moisture on the surface will cause the coating to fail and therefore climatic conditions are measured prior to coating to prevent any failures. Single or multi coat systems are applied in line with customer or paint manufacturer's specifications. The wet film coating thickness is then measured, to check that it will cure to the specified dry film thickness. Finally, the dry film thickness is measured to ensure it complies with the specification.
Several very important processes are followed throughout the coating process:
- Surface preparation: Abrasive blast to customer and/or paint manufacturers specification
- Measurement of surface profile to customer and/or paint manufacturers specification
- *Climatic conditions (Dew point, relative humidity, surface temperature, air temperature and dew point) are measured prior to any coating being applied
- *Immediately after coating the wet film thickness is measured to check that the applied thickness will cure to the specified dry film thickness
- *After the coating has cured the dry film thickness is measured in relation to the customer and/or paint manufacturers specification
*Individual inspection for each layer for multiple coat applications.
What is the importance of these processes?
Surface preparation is the essential first stage treatment of a substrate before the application of any coating. The performance of a coating is significantly influenced by its ability to adhere properly to the substrate material. It is generally well established that correct surface preparation is the most important factor affecting the total success of surface treatment. It affects the performance of the coating more than any other variable.
Surface preparation creates a foundation for the coating mechanically and chemically:
- Mechanically: By providing an anchor/key for the coating
- Chemically: By allowing intimate contact of coating material molecules with the steel (or other material) surface
Steel, when it is abrasive blasted, has a surface that is rough, with a series of tiny peaks and valleys called surface profile. Coatings anchor to the valleys of the profile and the peaks are like teeth. This is why the surface profile, created by blasting is called an "Anchor pattern" or a "Mechanical tooth".
The surface is blasted to standard grades of cleanliness in accordance with ISO 8501-1 1988 (BS 7079 Part A1 1989). This standard essentially refers to the surface appearance of the steel after abrasive blast cleaning and gives descriptions with pictorial references of the grades of cleanliness. Generally, Class Sa 2.5 is the most common:
Sa 1: Light blast cleaning
Sa 2: Thorough blast cleaning
Sa 2.5: Very thorough blast cleaning
Sa 3: Blast cleaning to visually clean standard
The surface profile is specified independently from cleanliness. The surface profile is created by the abrasive blasting. The correct height of the surface profile is essential, as it effects the coatings overall performance. There is no standard surface profile height that is suitable for all coatings. Basically, the surface must be roughened to get the coating to adhere to the surface. This is specified by the coatings (Paint) manufacturer. Generally, thin coatings require a low anchor profile. Too heavy a profile will result in the peaks of the profile in the steel sticking out and causing pin point rusting. However, thick coatings require a deep anchor.
Optimal environmental conditions are essential for surface preparation, application, and curing of coatings to maximise successful performance.
Surface preparation and the application of coatings should be performed under optimum environmental conditions to help prevent failures. The following conditions should be observed:
- Air temperature
- Surface temperature
- Relative humidity (RH)
- Dew point temperature
- Delta T: The difference between the surface and dew point temperatures
It is commonly known that most coatings will not dry properly at low temperatures and high RH. Surface moisture has a significant impact on the life and performance of the coating.
Moisture forms on a surface when warmer, moist air comes into contact with it (condensation). Moisture will cause unprotected steel to rust. If it is trapped between a coating and a substrate, moisture will likely cause the applied system to fail prematurely.
Instruments are used at Stainless Restoration to help assess the risk of moisture forming on the surface. Tests are performed to calculate the dew-point temperature before, during and after the coating process. Dew-point temperature is compared to the surface temperature to ensure the two are far enough apart that moisture formation is unlikely.
Careful observation of atmospheric conditions and a good understanding of their impact on the quality and long term health of coating are essential. Documents such as ASTM D3276 and the international standard ISO 8502-42 state that the surface temperature must be a minimum o