Coating is one of the most frequently used material in petroleum, chemical, mechanical and traffic engineering. It can not only beautify the environment, but also protect and decorate each part of the object, thus improving the quality of the coated object and extend its service life. "To the quality of paint film, coating contributes 30% and application 70%". The problem of paint film may be caused by the coating quality before application, or occur during or after application. There are many reasons for the paint film fault, and sometimes many reasons may be cross-linked, resulting in serious consequence. Damage caused during the use of paint film may also act as a reason of faults.

In recent years, after observing the application process and quality of coating, it is found that unskillful constructor, incorrect treatment of substrate and improper application environment are common reasons of unsatisfactory coating application quality like orange peel, sagging, whitening, bleeding, powdering, winkle, fish eye, pit and shrink hole, and even blistering and peeling, affecting the final decoration and protection effect. There are usually three kinds of application methods, brushing, roller painting and spraying.

The main reasons of paint film faults are as follows:

1. Coating quality problem

Coating quality problem is problem generated during production, storage or other processes of coating, finally resulting in defects of paint film after application. Coating quality depends on the binder used and its nature, the ratio of binder, pigment and filler, fineness of pigment and filler and their distribution status in binder, the additives and dosage, etc. Common faults include: paint film particle, powdering and orange peel.

2. Status of application substrate

The quality of substrate has importance influence on the forming and the final durability of paint film. It depends on the substrate material, application procedure, surface roughness, humidity, acidity, maintenance period, substrate treatment and the quality of putty used. The common faults include whitening and bumps.

3. Application process

If the application method is correct and the application process design is reasonable are also key factors affecting the paint film quality. The thickness of paint film, application procedures, whether the primer matches the top coat and recoat interval also have direct influence on the paint film quality. The common fault includes lifting.

4. Application operation

It includes whether the coat is stirred evenly before application, whether the application ratio meets requirements and whether the application operator is skillful and proficient, which is mainly problems caused during operation process of application operators

5. Application environment

It refers to the climate conditions for application and conditions on the application site, including temperature, humidity, weather, indoor ventilation condition, if the application system is properly chosen, the paint system used is matched, if the thinner used is appropriate and if the application surface and application tools are clean.

6. Application equipment

Incorrect quality or running conditions of application machine, or the machine is not correctly used may lead to paint film faults, for example, if the water and oil is not well separated, the air compressor will have run oil; if the oil discharge amount of spray gun is not well adjusted, there will be orange peel or sagging.