Common problems and preventive measures in coating construction

 "Inexperienced construction workers often have problems such as peeling, pinholes, and blistering when spraying paint.

 What is causing such a problem? How to prevent and solve?"

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1. Peeling 

Undercutting refers to the phenomenon of peeling and peeling caused by the solvent in the upper coating that softens and swells the bottom paint film, resulting in poor adhesion of the bottom paint film.

Causes:

(1) The topcoat film is too thick, swelling the underlying primer, causing the primer coating to wrinkle and cause biting; 

(2) The topcoat is sprayed before the primer coating is not dry;

(3) The primer does not match the top coat. For example, the primer uses polyurethane paint series, and the top paint uses acrylic paint or epoxy paint; 

(4) If the bottom putty is not dry, start applying the primer, then when applying the top paint, the primer It will be melted up, resulting in a "bottom biting" phenomenon.

Prevention and solution: 

After the bottom coating is completely dry, brush the surface coating. The operation should be accurate and rapid to prevent repeated brushing. For serious undercutting phenomenon, it is necessary to remove the coating completely, and then select the same kind of coating to brush after the base is dry.

2. Pinholes

The pinhole phenomenon of the paint film refers to the phenomenon of pinpoint pores that appear on the surface of the paint film. This needle is small in shape, like a needle-punched hole, with a diameter of about 100 mm.

Causes:

(1) The viscosity of the paint is too high, one coat is thick, the filling hole does not contain air; 

(2) The spraying air pressure is too high, the paint is mixed with too much air;

(3) Oil, dust and sweat are attached on the coated surface, and the water is accumulated around these impurities;

(4) When the coating is dried by heating, the temperature is too high, the standing time is not enough before the coating is heated, the solvent is not fully volatilized, bubbles are brought into the coating itself, and the bubbles generated during mixing are not eliminated.

Prevention and solution: 

Check the coating process conditions, adjust the appropriate coating viscosity, use appropriate amount of diluent and curing agent to control the thickness of the coating; improve the working environment and control the appropriate temperature and humidity; after the coating is prepared, it should stand for 20 minutes before spraying; when heating and drying the coating, control the standing time to make the solvent fully volatilize, and then preheat the coating.

3.Blistering

Blistering means that a part of the coating film bulges upward from the coated surface or the base coating, and contains moisture or air inside, and the size is 0.5 mm ~ 5 mm in diameter. Most of the time it appears in pieces, rarely appears alone, similar to the human Prickly heat in hot and humid weather.

Cause:

 Generally speaking, there are far more opportunities in the topcoat than between the paint and the substrate. The bottom line is moisture or dirt trapped under the paint film. Solvent bubbles or stirring air bubbles are mostly caused by bottom pollution or insufficient cleaning, tool pollution, poor spraying environment, or unmatched curing agent or thinner, etc., which will appear at the same time as spraying, while bubbling defects caused by water vapor are generally sprayed. After the shortest few minutes, the longest to appear after more than a month.

Prevention and solution: 

Use a nail to break the bubble to determine the depth of the bubble, and use a low-power magnifying glass to find out the cause of the bubble. When air bubbles occur between the paint layers, the defective area can be polished off, and the paint layer is exposed before repainting. If the defect is serious or air bubbles occur between the primer and the substrate, all the paint layer on the substrate should be removed and then sprayed again.

END --Thanks to reading.