What does SA 2½ mean?
This indicates the extent to which the surface has been cleaned after blasting.
ISO 8501: The guideline behind SA 2½
In 1988, the International Standards Organisation (ISO) released the guideline ISO 8501 entitled ‘Preperation of steel substrates before application of paints and related products’. It combines guidelines from Sweden (SIS 055900) and Germany (DIN 55928) and includes illustrations showing what each cleaning level looks like on different surfaces.
ISO 8501 divides cleaning levels into three categories:
- SA 1: Light blast cleaning
- SA 2: Thorough blast cleaning
- SA 3: Blast cleaning to visually clean steel
Later, ISO added a new level, SA 2½ (Very thorough blast cleaning), to provide a cheaper alternative to the highest level when near-perfect cleaning is not needed.
Note: SA 2½ indicates how clean the metal is after blasting, but it says nothing about its roughness!
-
Features of SA 1
Light blasting, also called ‘Sweep blasting’ or ‘Brush-off blasting’.
- Loosely adhesive material: 0%
- Strongly adhesive material: 100%
- Stains, streaks, shadows: 100%
This is used to remove loose rust, mill scale and old coatings. Good bonding materials may be left on the surface. This is hardly used anymore in preparation for coating.
-
Features of SA 2
Thorough blasting, also called Commercial blasting.
- Loosely adhering material: 0%
- Strongly adhering material: 0%
- Stains, streaks, shadows: 33%
Commercial blasting removes strongly adhering material, but allows up to 33% of the surface to have shadows, streaks or stains. It is used when a high level of cleanliness is needed but not perfection, which is common when repainting in less corrosive environments such as tanks and bridges.
-
Features of SA 2½
Very thourogh blasting, also called ‘Near White’ blasting.
- Loosely adhering material: 0%
- Strongly adhering material: 0%
- Stains, streaks, shadows: 15%
Here, shadows, streaks or spots are allowed on up to 15% of the surface. It is chosen when it is not worth blasting to white metal (SA 3). Usually used for high-performance coatings in harsh environments such as offshore platforms, shipyards and other marine environments.
-
Features of SA 3
Blast cleaning to visually clean steel, also called ‘White Metal’ blasting.
- Loosely adhesive material: 0%
- Strongly adhesive material: 0%
- Stains, streaks, shadows: 0%
This is the highest standard of blasting, where no shadows, streaks or stains are allowed. It is necessary for extreme conditions such as high temperatures or corrosive environments where failure of the coating could have serious consequences, such as in nuclear reactors, turbines or submarines.
Why is this standard important?
To make coatings last longer and save costs, it is important that the surface is clean after blasting because:
- Adhesion of coatings: A clean surface ensures better adhesion of coatings, such as paint or other protective layers, making them adhere better and last longer.
- Corrosion prevention: Cleaning removes contaminants such as rust, dirt and old coatings, reducing the risk of corrosion and extending the life of the metal and applied coating.
Surface preparation can take up to 40% of the total cost of repainting. Owners want to spend less on materials and blasting time. The highest level of cleanliness, ‘White Metal’ (SA 3), is expensive and mainly used for critical situations. For most jobs, ‘Near White’ (SA 2½) cleanliness is good enough and is therefore most often prescribed.
Discover our machines
Discover Gritco's high-quality equipment, developed from 34 years of experience and expertise. Optimise the speed and quality (and therefore SA cleanliness!) of your blasting with the right blasting machine and abrasive.
