Lecture: Surface Preparation Techniques and Painting
TA :
Facilitate the training activity by video/slide presentation and demonstration of procedures in painting in accordance with safe working practices and manufacturers guidelines.
LA :
Students shall:
- Explain the causes of corrosion and the corresponding methods of its prevention
Demonstrate the procedures in painting in accordance with safe working practices and manufacturers guidelines
Water—it’s essential for life, but also one of the most destructive elements on the planet. On ships, the corrosive environment caused by salt water and marine growth can lead to structural weaknesses, as well as logistical and financial inefficiencies. Without the proper ship surface preparation before applying anti-corrosive coating, the coating will not adhere to a ship as well and will prematurely break down.
Surface Preparation Techniques
Preparing a ship’s surface is a vital part of preserving it. It is also the most important factor in regards to the performance of the protective coatings applied. Several preparation techniques can be accomplished using hand and power tools. Determining the best technique depends on the ship’s substrate and the coating manufacturer’s recommendations. The most common techniques include:
- Hydroblasting: Technicians use high-pressure jets of water to clean a surface and spray off loose paint, salt, dirt, oil, and some rust, eliminating the need for abrasives. This technique negates problems caused by dust and spent abrasives.
- Rotary wire brushing: Hardwire brushes remove powder-like rust, but not rust scale that’s attached to the substrate. The brushing may make the surface of the rust scale looked polished. Technicians may use wire brushing prior to mechanical de-scaling.
- Rotary power disking: A preparation method that uses silicon carbide disks. There are various disk types and grit sizes, which are effective at cleaning pitted and irregular surfaces.
- Mechanical de-scaling: Technicians use pounding-type instruments or cutting blades to remove thick rust and scale, and partially clean disintegrating brittle scale. De-scaling, however, does not remove the lowermost layer of rust or scale on the ship’s substrate.
- Abrasive blast cleaning: A technique that leaves surfaces rough and well-suited for most coatings. This is a common preparation method that uses compressed air to remove paint, salts, rust, dirt, and mill scale. While the technique is effective, it is one of the most common sources of shipyard pollution and waste. Improper blasting techniques may lead to higher levels of salt and contaminants on a ship than before the blasting process.
- Solvent cleaning: Technicians use detergents to remove dirt, oil, and grease on a ship’s surface before blast cleaning it. If not used correctly, solvents may thinly spread contaminants on surfaces instead of removing them.