The protective properties of paint have no effect unless the paint is applied correctly. Many people think that all the problems are solved as soon as the anti-corrosive paint is applied in the specified film thickness. It is, however, a fact that the method of application can be equally important with regard to the final result. The following general guidelines for application are recommended:
- All coating systems must be applied in accordance with their product data sheets.
- Application must take place under controlled climatic conditions suitable for the particular product in use.
The paint must be applied by means of the most suitable equipment and correct application technique.
Methods of application include the following:
- Roller Airless spray
From a technical point of view the ideal method of applying a paint is with a brush. The advantage of brushing is that the paint is worked well into the surface so that gaps, pores and pits are filled up, for example in uneven welding seams. Also the paint brush is moved back and forth, moving the paint or coating in two or more directions. Each of these actions makes the coating flow over the surface in several directions, increasing the intimate contact of the paint with the surface. This is particularly valuable where a coating with only low wetting characteristics is applied.
Another action of the brush is that of stippling or dabbing the coating on to the surface. This is particularly important when applied around bolt heads, rivets, welds, and in corners. Such a movement aids in filling pinholes, pits and rough surfaces with the coating. In many cases the physical action created by using the brush is the only one that can make the coating flow into these areas.
Neither rolling nor spraying will do this so well.
Application by roller is a commonly used method. Rolling is primarily suitable for areas large flat are such as the exterior of a tank or the flat side of a ship.
Experiments and practical experience have shown that application of the first coat with a roller is not to be recommended. This is particularly true on surfaces where the pretreatment has not been ideal or where moisture or other impurities having collected on the surface. Areas generally not suitable to be coated with a roller are:
Complicated structures, porous or uneven surfaces, corners, sharp edges, along areas with many bolt heads or rivet heads.
A paint roller may be used with good results for subsequent coats.
Application by Spraying
A paint brush is not a very practical choice when painting large areas. Here paint spraying equipment is a more effective alternative. The most important advantages of spray-application are:
- It gives a very high production rate and is suitable for large jobs.
- All coats, including the first, may be applied by airless spraying.
- Airless spraying, when used correctly, offers the advantages of giving a higher film thickness per coat.
- A much more even film thickness is obtained.
The major disadvantages of spray- application are:
It requires a lot of training / practice to apply an even film to a predetermined thickness, with no defects and a smooth surface.
- It is not suitable for application in narrow gaps or areas with difficult access (Like rat holes, behind corners etc.)
- Location and surrounding environment may be affected.
High-pressure spraying is used for application of most types of coating used to protect ships, offshore structures and industrial plants. Paint application using airless spraying must be carried out correctly in order to obtain satisfactory results.
- It is very important that the spray-gun is kept in constant motion.
The spray-gun must be held at the correct distance from the substrate, i.e. about 30-60 cm (12-24 inches).
- The gun should be held perpendicular to the substrate
- Each stroke should overlap the previous stroke by 50% or cross application.
- Difficult areas such as profiles, corners, edges, etc. are sprayed first. The other surfaces are subsequently sprayed.
- The wet film thickness should be controlled continuously during spraying.
- Always remember to choose the correct nozzle for the job.