When preparing a surface for coating it is important – apart form cleanness – to get a structure of the surface that offers optimal adhesion of the coating. This adhesion is ensured by obtaining a suitable degree of roughness and structural shape.

In case of high roughness heights the consumption of paint is higher than for lower roughness heights. It should also be taken into account that the applied coating thickness of the paint should correspond to the obtained roughness height.

Roughness and structural shape depend on:

the abrasive:

• shape of the grain
• composition of the operational mixture
• hardness of the abrasive
• toughness of the abrasive

the blasting unit:

• nozzle (shape of the nozzle)
• pressure – discharging speed

the material to be blasted:

• hardness
• intensity of the jet

the blasting device:

• impact angle
• distance between workpiece – nozzle
• nozzle movement and guidance.

Example: Different abrasive grains (steel shot)

Ra = medium roughness value
Rmax = maximum roughness height
Rz = averaged roughness height