Surface preparation before painting any kind of steel is key to ensuring the longevity of metal paint and other coatings. 

Good surface preparation

Proper surface preparation is essential and one of the preconditions for a long lasting protective coating systems.

The classifications of the coating systems are based on minimum requirements for surface preparation.

The minimum preparation grade (if not otherwise specified, or agreed) for carbon steel rust from grades A, B, C, is blast cleaning to SA 2 1/2 (ISO 8501-1).

Surface Preparation

ISO 8501 – Condition of steel identification A, B,C.D.

1. Steel surface largely covered with adherent mill scale. Little if any rust.
2. B. Steel surface which has begun to rust and from which mill scale has begun to flake.
3. Steel surface on which the mill scale has rusted away or can be removed by scraping but with slight pitting visible under normal vision.
4. D. Steel surface on which the mill scale has rusted away, and general pitting is visible without magnification. 

GRADES OF SURFACE, ACCORDING TO ISO 8501-1:

Sa3 Blast cleaning to visually clean steel

When viewed without magnification, the surface shall be free from visible rust oil, grease and dirt.

Sa2-⁄ Very thorough blast cleaning

When viewed without magnification the surface shall be free from oil grease and dirt, and free from mill scale, rust paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.

Sa2 Thorough blast cleaning

When viewed without magnification the surface shall be free from oil grease and dirt, and free from most of the millscale, rust paint coatings and foreign matter. Any residual contamination shall be firmly adhering.

Sa1 Light blast cleaning

When viewed without magnification the surface shall be free from visible oil grease and dirt, and poorly adhering mill scale, rust paint coatings and foreign matter.

St3 Very thorough hand and power tool cleaning

As for St2, but the surface shall be treated much more thoroughly to give a metallic sheen arising from the metallic substrate.

St2 Thorough hand and power tool cleaning

When viewed without magnification, the surfaces shall be free from visible oil grease and dirt, and poorly adhering mill scale, rust, paint coatings and foreign matter. 

 

__

 

Pronto Paints have been working in structural steel for over 30 years and have an exhaustively researched range of coatings for steel.

Want to book a callback or arrange a coating trial with one of our in-house experts? Drop an email to info@prontopaints.com

 

__

View our structural steel products range here. 

Download the ISO12944 Guide to Structural Steel Coatings here 

 

Recommended reading

What are the main challenges in maintaining and coating structural steel assets?

What are the benefits of using specialist industrial coatings for structural steel?

What is the best type of paint for structural steel?

How do I select the right coating for my structural steel project?