A coating on a steel structure will only last as long as the surface underneath. You can buy the most expensive paint system on the market — when applied to scale and rust, it begins to flake off.
That is why the steel is blasted before painting.
What jetting does
Blasting is a process in which an abrasive is thrown at the surface of the steel at high speed. It removes three things from it:
- scale — a layer of oxides that forms on steel during hot rolling
- rust — corrosion products
- old paint and dirt
And it adds one more thing: the anchor profile. The blasted surface is not smooth, but microscopically broken — and the coating is mechanically anchored to it. It would just lie on smooth steel.
Degrees of cleanliness according to ČSN ISO 8501-1
The standard distinguishes four degrees of blasting:
| Degree | What does it mean |
|---|---|
| Sa 1 | light blasting — only loose layers removed |
| Sa 2 | thorough — most scale and rust removed |
| Sa 2½ | very thorough — only trace shadows remain |
| Sa 3 | visually clean metal |
Sa 2½ is the standard for quality coating systems. No scale, rust or old paint should remain on the surface — only light shadows in the form of spots or streaks.
Sa 3 is even cleaner, but it is not normally required for building constructions and significantly increases the cost of preparation.
Why ask the supplier?
The level of surface preparation is almost never mentioned in offers. And at the same time, he decides whether the structure will last for fifteen years, or if it will begin to peel off in five years.
When the menu just says "finish: paint", ask three things:
- What is the degree of surface preparation? (expected answer: Sa 2½)
- What is the thickness of the coating system in microns?
- For what degree of corrosion aggressiveness is the system designed? (C1 to C5 according to ČSN EN ISO 12944)
The difference between hand-cleaned steel and blasted to Sa 2½ will be reflected in the price by one percent. In life by years.
With what we jet
We have a Gietart Eco Blaster 1504 blasting device in production. Blasting to Sa 2½ is our standard preparation before painting, not an extra charge.
We use it for the construction of our own buildings and for external customers — we offer steel blasting as a separate service.
Where we use it
Blasting to Sa 2½ followed by a 120-micron polyurethane coating is a common specification for us — for production halls, agricultural buildings and structures for aggressive environments.
In operations where the humidity is permanently higher or where dust and chemicals remain in the air, the difference between careful preparation and aftermarket preparation will become apparent within a few years.
Inquire about blasting or check out ours steel structure.
