Paint Application: Best Practices and Quality Control

Posted on Jan 22, 2025 in Civil Engineering, Transportation, and Urban Services

Recommendations for Implementation and Control

• Surfaces must be dry, and the humidity and temperature should be such that they do not lead to condensation but produce vapors.
• If the surface is hot, it can lead to boiling of the paint, causing craters and blisters.
• At the reception, check the labels of the containers. The container must not be beaten. Stir, let stand for one hour, and apply within the six hours that follow; if more time passes, it no longer works.
• At the end of the day, all the equipment must be cleaned.
• Before painting, seal areas of overlap and areas of contact between different materials with mastic.
• In areas of angles, edges, etc., a primer should be applied first to prevent the paint from becoming too thin.

Common Paint Defects

• Poor Brushability: This may be due to low temperature, an inappropriate brush, too rapid drying, or combing and retouching the paint when the surface layer has begun to dry.
• Slow Drying: This can be caused by excessive film thickness, low room temperature, relatively high humidity, heavy use of solvents, and lack of ventilation.
• Sagging: This results from a downward movement after application and before its fixation by drying, resulting in areas of different thickness. It may be due to excessive layering, excessive dilution, and excessive use of heavy solvents.
• Loss of Gloss: This is caused by excessive dilution of the paint, condensation of humidity, absorption of the binder when applying the paint on a very porous substrate, use of improper solvent, or not completely drying the surface when using an exterior-resistant paint.
• Lack of Adhesion: This can occur due to excessively smooth surfaces, lack of pre-primer on substrates with an excessive level of moisture, grease, or dirt on the surface, or because of debris from flaking old paint.
• Poor Hiding Power: This can be caused by excessive contrast between the background and the paint, applying a layer that is too thin, or low consistency of the paint.
• Wrinkling: This is an effect in the form of folds formed during drying. It is caused by excessive layering, refinishing paint on a dry surface, and applying a coat with harsh solvents that soften the background layer.
• Craters: These are small depressions that are caused by a lack of wettability between coats. It is caused by poor cleaning of the surface, contamination during the painting process, and incompatibility due to inadequate mixing.

Quality Control: Liquid and Dry Film

• Viscosity: Measured with a viscometer.
• Density: Measured with a hydrometer.
• Fineness: To know the specified degree of dispersion. To do this, use a fineness gauge.
• Flash Point: Measured using the closed-cup method.
• Gloss: Compared with a sample type or measured with a gloss meter.
• Opacity: Measures the ability of an opaque paint on cardboard with black and white stripes. Apply a coat of paint on cardboard, and when dry, check the contrast with the background paint.
• Thickness: Measured by a comb whose spines have different lengths. If we penetrate this comb in the film to its base, some paint-stained quills will be stained, while others will not. It is measured in micrometers.
• Hardness: There are several devices, but the most widespread is the Persoz pendulum.
• Flexibility: Measured by the bend test.
• Adherence: Measured by the cross-cut test.