Besides the degree of cleanliness – the removal of oil and grease, rust and mill scale, dust, and other contaminants – surface preparation specifications must also consider the surface profile and roughness relative to the coating to be applied. Rosler Metal Finishing builds shot blasting equipment to create the right surface profile on structural steel components as well as cleaning them in preparation for coating and painting.
This installment of our Structural Steel FAQ series will answer What is the optimum the surface profile for a structural steel component prior to painting and how is profile evaluated?
Optimizing for Painting
Shot blasting makes a surface rougher to increase the total contact area between paint and a work piece substrate and generally improves paint adhesion. A surface that is too smooth poses the risk of inadequate paint adhesion, while a surface that is too rough may not cover the peaks. The degree of surface profile required depends entirely on the coating to be applied.
As an expert in the surface finishing industry, Rosler Metal Finishing knows that all the expertise in the world won’t do any good if the surface of the work piece is not properly prepared. When it comes to structural steel, we receive many frequently asked questions about preparation. This installment of our Structural Steel FAQ series will answer How is the presence of dust on shot blasted structural steel components evaluated?
The Dangers of Dust
Blast-cleaned structural steel surfaces must be completely free of dust to ensure proper coating and painting.
Residual dust will reduce the adhesion of subsequently applied coatings and, by absorbing moisture, may promote the corrosion of the blast‐cleaned steel surfaces. The potential accumulation of dust is especially critical on horizontal surfaces, the interior of pipes, and in structural cavities.
Special inspections must be carried out to ensure that such areas are adequately cleaned and free from dust before painting.
Surface preparation can account for up to 40 percent of structural steel painting and repainting jobs. As Rosler Metal Finishing’s Structural Steel FAQ series has already established, the life of anti‐corrosion coatings on a steel surface depends to a large extent
on how thoroughly this surface has been prepared for painting.
Properly evaluating the surface of structural steel surfaces for coating before and after shot blasting will help balance the cost of preparing, repairing, and monitoring structural steel throughout its impressive lifespan.
This installment of our Structural Steel FAQ series will answer How are rust and mill scale evaluated pre‐ and post‐blast?
Widely used standards were developed to visually assess the initial surface conditions and the quality of the required surface preparation relative to the initial steel surface conditions.
The dominant standards for evaluating rust and mill scale are ISO 8501‐1:2007 (based on the Swedish standard SIS 05 59 00), SSPC Vis 1‐89, and NACE. While different in some minor details, these standards are practically identical.