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Surface contaminants and their impact on coatings projects

Customers or end users demand an increasingly high level of quality for their new construction or industrial coatings maintenance projects.

The expectations of durability of the protective coating systems is increasingly high reaching the request for durability greater than 15 years before it is necessary to carry out the first maintenance of the protective system of an asset or structural element that was prepared and treated at the time. according to the customer’s specifications.

One of the most important aspects in a coating project is the elimination of surface contaminants. Surface contaminants prevent the correct behavior of a coating system.

Pollutants are impurities that may come from the environment or from manufacturing or assembly processes or operations. These contaminants can be visible as in the case of dust, grease, oil, rust, rust and other foreign matter or not visible as the case of soluble salts and some films of oil or grease that are not visible to the naked eye and must be evaluated properly.

How do contaminants affect coatings?

Contaminants present in a surface that affect coatings projects can be divided into three main groups:

– Contaminants exposed on the surface.

– Contaminants in the environment susceptible to adhering to the surface.

– Contaminants in the product or equipment.

Contaminants often influence the performance of the coatings in both the adhesion of the coating system to the base material and the adhesion between layers of the coatings.

The specifications are not clear when determining the amount, frequency and type of contaminants that may remain on a surface before applying a coating, as well as the methods of measurement and testing to measure the presence of these contaminants.

Any contaminant trapped in the metal or bare material to which a treatment, coating or paint is subsequently applied, will impede the correct development of the same, creating defects or imperfections in the coating, greatly affecting the adhesion of the same with the base material . This will lead to premature failures in those areas and the probable need to have to carry out maintenance work ahead of schedule, incurring extra costs.

Engineers or personnel who write technical specifications should take into account the following when specifying:

– Realistic durability of the protective system.
– Initial condition of the structure.
– Work environment.
– Storage of the structure in project.
– Surface preparation and treatment processes.
– Logistics and possibility of environmental control.
– Quality control of products and equipment.
– Pollutants allowed and not allowed on the surface.
– Inspection method.
– Acceptance and rejection criteria.
– Cost of removing pollutants to the desired degree.

The specifiers must know in detail the rules for cleaning surfaces at the time they will describe a degree of cleanliness for the application of the coating. The series of ISO, NACE and SSPC standards for surface cleaning refers to the type of visible contaminants that may or may not remain on the surface when it is evaluated without increases.

There is a great variety of contaminants that when evaluated with increases or other methods can be detected in a surface and these can affect the correct performance of the protective system. There are different industries with different criteria when defining the presence or elimination of surface contaminants in the substrate, base material or between layers before applying a coating or inclusions in finishes of non-permitted coatings, such as the case of the I already.

The specifier must establish the requirements as to the type and quantity of contaminants that may be present in a surface if any are allowed. In the case that the presence of contaminants is allowed up to a certain point, it must be properly delimited, as well as its method of inspection and acceptance and rejection criteria.

The main equipment that a technician or inspector should have when evaluating surface contaminants in a coating project are:

– Flashlight 500 Lux or higher.
– Kit for evaluation of surface dust according to ISO 8502-3.
– Kit for the evaluation of soluble salts on surfaces.
– Test strips to evaluate the PH.
– Anemometer to assess the wind speed and foresee the inclusion of pollutants