When large areas are waterblasted, flash rusting which deminish the original surface standard may occur, before painting can be carried out. The degree of flash rusting depends on many factors, such as humidity level, temperature and the length of time the surface is exposed.
The use of hydro blasting will cause the temperature of the steel to rise. The increase of temperature of the steel surface can be substantial, depending on the pressure of the equipment used and will help waterblasted surfaces to dry off faster, hence reducing the degree of flash rusting.
The use of water has the advantage of removing oil and grease from the surface along with salt deposits. This is a major plus point of hydro blasting. The grey, brown to black discoloration of corroded and pitted steel after hydro blasting cannot be removed by further blasting. Studies shows that this thin film consists of mainly ferric oxide, which is an inert material. As it is tightly adherent, it does not present a serious contamination problem.
Hydro blasting will not produce a surface profile as such. Weakend steel might erode, resulting in metal loss, but the surface profile exposed after blasting will have been produced by earlier surface preparation or corrosion.