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Contaminants on the surface and their impact on coating projects

Durability expectations of protective coatings systems are becoming higher, even coming to request for a durability larger than 15 years before it is necessary to carry out the first maintenance of the protective system of an active or structural element that was once prepared and treated according to client specifications.

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

Contaminants are impurities that may come from the environment or from the processes or operations of manufacturing and assembly. Such contaminants may be visible as in the case of dust, grease, oil, rust and other foreign or non-visible matter such as soluble salts and some oil or grease films which are not visible to the naked eye and they must be adequately evaluated.

How do contaminants affect coatings?

Contaminants present on a surface that affect coating projects can be divided into three main groups:

- Contaminants exposed on the surface.

- Contaminants in the environment susceptible to adhere to the surface.

- Contaminants in the product or equipment.

Contaminants often influence the performance of 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 can remain on a surface before applying a coating, as well as measurement and testing methods to measure the presence of these contaminants.

Any contaminant trapped in the metal or bare material to which a treatment, coating or paint will subsequently be applied, will prevent the proper development thereof, creating defects or imperfections in the coating, greatly affecting the adhesion thereof with the base material. This will lead to premature failures in those areas and the probably need to carry out maintenance work ahead of schedule, then incurring extra costs.

Engineering companies or staff writing technical specifications should keep in mind these points when specifying:

  • Realistic durability of the protective system.
  • Initial condition of the structure.
  • Work environment.
  • Storage of the project structure.
  • Processes of surface preparation and treatment.
  • Logistics and possibility of ambient control.
  • Quality control in products and equipment.
  • Contaminants allowed and not allowed on surface.
  • Inspection method.
  • Acceptance and rejection criteria.
  • Cost of removing contaminants to the desired degree.

Specifiers should know in detail the rules for cleaning surfaces at the moment they are going to describe a degree of cleaning for the application of the coating. ISO, NACE and SSPC series standards of surface cleaning mentions the type of visible contaminants that may or may not remain on the surface when it is evaluated without magnification.

There is a wide variety of contaminants that when evaluated with magnification or other methods, they can be detected on a surface and can affect the correct performance of the protective system. There are different industries with different criteria when defining the presence or removal of surface contaminants in the substrate, base material or between layers before applying a coating or even inclusions in finishes of non-allowed coatings, as in the case of the yacht.

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

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

  • 500 Lux or higher hand flashlight.
  • Kit for the evaluation of surface dust according to ISO 8502-3.
  • Kit for the evaluation of soluble salts on surfaces.
  • Test strips to evaluate PH.
  • Anemometer to assess wind speed and predict the inclusion of environmental contaminants to the surface.
  • Surface cleaning standards and visual comparators.
  • Kit for evaluating chalking or plastering.
  • Kit to evaluate the exudation of amines.
  • Ultra violet flashlight to detect the presence of oil and grease that are not visible.

Conclusion: The contaminants prevent the correct performance of the coatings. Most premature failure due to the presence of surface contaminants can be avoided with a correct specification, inspection and supervision of painting works, which will significantly increase the durability of their protective systems.

In many cases, failing to adequately specify the level of contaminants allowed on surfaces, as well as establishing the proper control or inspection method can lead to extra costs in the project that can be solved with appropriate advice.

For more information when specifying, establishing or meeting with the technical requirements of your coating project, you can contact Optimiza and its independent on-site or online consulting service on Corrosion and Coatings at optimiza@optimizaconsulting.es or visit our website www.optimiza.es

Optimiza has independent consulting packages adapted to all users: end clients, engineering companies, boiler and assembly companies, coating applicators, product and equipment manufacturers and other kind of users in the industry.

For more information about Inspection technology to detect surface contaminants and other methods of inspection of surface preparation and application of coatings, please contact Optimiza Store at info@optimizastore.com or visit our website www.optimizastore.com