Coating Inspections and Quality Control - Dekro Paints

Coating Inspections and Quality Control

Every painting project creates the expectation that painted structures will be protected for a minimum period of time as set aside by the paint manufacturer. Clients rely heavily on tools such as the specifications, contractor certification, quality control, and quality assurance inspection to verify that the work is performed as specified. While many projects require quality control and/or quality assurance inspections, few specifications, if any, differentiate between the two or provide guidance on the responsibilities of each.

Many would agree that the quality of applicators and their nominated sub contractors have declined in the past 5 -10 years and this has resulted in the increase of independently appointed consultants and project managers to oversee the painting projects for the clients. In-house quality control should still be the highest form of control as preparation and application of products counts for 90% of paint failures within the painting industry

Specifications only establish minimum standards of practice for quality control and quality assurance and this article concludes with recommendations for maximizing the benefits of both quality control and quality assurance.

What is the difference between quality control, QC and quality assurance, QA?

Quality control is performing the necessary observations, testing, and documentation to verify that the work performed meets or exceeds the minimum standards established by the project specifications or contract. QC is the contractor’s responsibility. Quality assurance is an audit process to verify that the quality of work performed is what was inspected and reported by the contractor’s QC. QA is conducted by the owner or by a third party inspector on the owner’s behalf.

Specifications

Modern specifications usually comprise a sequential coating application of paints … one coat on top of another and each coat has a specific function / purpose.

Specifications should consider all the defects and possible repairs and should be amended during the course of the project when the scope of works changes. The following conditions and aspects should be considered.

Ambient Temperatures

Coatings are generally tested at 23-25 Degrees Celsius (normally confirmed within the TDS, Tecnical Data Sheet) and if ambient temperatures are below this the drying times of the product will increase. Certain pure acrylics will start forming craters when applied as the surface is probably to cold to apply coatings. {Refer to Dekro Paints identifying problems page.

Steel temperature must be a minimum of 3°C above dew point, measured in the vicinity of the substrates.

Pre Surface preparation conditions

As a QC or QA you have to consider the possibilities that will cause paint failures, these includes but are not limited to…

Chalkiness, Efflorescence, Hairline cracks / mapping, Structural issues, Peeling paint, Cleanliness, Dampness, Mould/ Fungal growth, Paint discoloring and the type of coating currently on the substrate. All these defects must be noted and remedial action must be provided to insure coating adhesion will be possible.

Abrasive cleaning completion

Most specification and TDS documentation will stipulate the required cleaning methods to be completed and forms an integral part of the application process. Hydroblasting for masonry and wood surfaces or Blast cleaning on metal surfaces.

For all metal surfaces there is a choice between two general types of preparation:

1.      Blast cleaning to SA 2.5 Swedish Standard, or SIS SA 2.5

2.      Power tool cleaning, hand wire brush, chipping or scraping. Mechanical power tool cleaning is preferred. ST 1 / ST 2 or ST 3.

Mixing and Material

Site inspections are not only to ascertain if the specification is followed but also to determine if the correct materials are on site. Incorrect thinners can lead to solvent entrapment in coatings (Enamels, Chlorinated Rubber Coatings, Epoxies and Polyurethanes) and will cause paint delamination and other adhesion failures over a period of time.

Materials must also be stored correctly and paint containers not correctly sealed will evaporate moisture and affects the performance of the coatings.

Application Equipment

Budget constraints normally lead to the overuse of painting equipment and brushes and rollers no longer perform their tasks properly which causes inconsistent coating application and incorrect wet and dry film thicknesses.

Surface Preparation

Surface preparation is the most important part in the performance of any paint system. Prior to priming or painting it is essential to ensure that the substrate is sound, to remove any chalkiness, loose and flaking paint and ensure that the surfaces are dry, clean and free of any dust, dirt and grime.

If efflorescence and alkali burn is present the causes for this must be investigated. Using the correct primer and proper surface preparation is the foundation of a successful paint application. Paint must always be applied to a dry and sound surface. Regular inspections forms a critical part of the coating system.

Wet Film Thickness

Wet Film Thickness Gauges are designed to quickly and easily measure the thickness of coatings immediately after they have been applied to a substrate. These gauges are also commonly known as: Combs, MIL Gauges, Step Gauges and Notched Gauges. This is the most accurate way to insure that coatings are applied the correct thickness and corrective measures could be taken immediately if WFT is under the required thickness as per TDS.

Intercoat Cleanliness

Intercoat cleanliness includes rolling mist that carries salt laden air that contaminates the surface. By not removing this salt contaminated moisture from the walls will result in failure of coatings. Dust particles in condensed construction zones as well as Iron oxide dust contamination in industrial zoned areas can cause paint failures.

Dry Film Thickness

Dry film thickness (DFT) is the thickness of a coating as measured above the substrate. This can consist of a singlelayer or multiple layers. DFT is measured for cured coatings (after the coating dries). Thickness of a coating depends on the application and type of process employed. DFT’s should only be used as a guideline and batch numbers, volume solids, roughness of surface will all directly impact the DFT of a coating applies

Visual Appearance

For a complete list of common paint problems visit the identify problems page on our www.dekro.co.za website.

Conclusion

Only by establishing clear qualifications, responsibilities, and documentation requirements for both QC and QA on a given project will all parties to a protective coatings project benefit fully from a total quality management process.Benefits can include avoiding duplication of documentation and inspection, reducing conflicts among the contractor, o w n e r, and third party QA; real or perceived under- or over-inspection; and most importantly, long-lasting protection of the structure or asset.

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