Structural steel (low-alloy steel):

• The effects of oxygen and electrolytes (e.g. water) cause iron oxides (rust) to form on the surface.
• Unlike aluminium oxides, iron oxides are not firmly attached to the base material and must be removed prior to bonding.
• For ground surfaces there is a risk of belated chemical changes to the surface under the adhesive film (e.g. corrosion).