Let's analyze the common paint defects and treatment methods in the painting operation.
1. Wet blistering
Evenly distributed small bubbles in the shape of pits, of different sizes, are easy to appear under very humid and hot conditions. These bubbles will disappear when the air humidity decreases, and the paint film will become flat.
① Cause
▶ Insufficient adhesion between the topcoat, midcoat, primer and substrate may cause blistering.
▶ Paints are relatively permeable. Under very humid and hot conditions, water will penetrate into the paint film in liquid form, and then pass through the paint film in the form of vapor, forming wet bubbles.
② Correction method
▶ In humid weather, only dry grinding can be used, keep the compressed air dry, and ensure that the sprayed surface is completely dry before spraying.
▶ Do not place the sprayed parts in a humid and hot environment before they are completely dry.
▶ When the bubbles are not broken, you can wait for the water to evaporate and restore the paint film to its original state. In serious cases, you must thoroughly grind and re-spray. Stripping the paint to bare metal and re-spraying is the best choice.
2. Contaminated blistering is also called bubbles or "prickly heat", that is, irregular blistering occurs on the surface of the paint layer.
① Causes
▶ The main reason is the contamination of the substrate, and the lack of proper cleaning and preparation before painting.
▶ Contamination from the air supply pipe or spraying tools.
② Correction method
▶ Clean the spraying surface and thoroughly remove substances such as wax, grease and polishing agent.
▶ Ensure the cleanliness of compressed air, air supply pipes and tools such as spray guns.
▶ If prickly heat has occurred, gently polish the surface, be careful not to wear through the paint film, and re-spray. If the situation is serious, it should be polished to bare metal and re-sprayed.
3. Dust
After the topcoat is sprayed, there are foreign objects or dirty spots on the paint surface, and dust or dirt is wrapped in the paint film.
① Causes
▶ The spraying workshop is not clean, for example, there is no filter cotton on the floor of the paint room, and the filter cotton on the ceiling has not been replaced for a long time.
▶ The compressed air is not clean, the paint operator does not wear special work clothes, and the spraying surface is not clean.
▶ The paint is not effectively filtered before spraying.
② Correction method
▶ Keep the spraying workshop clean, replace the filter cotton in the paint room regularly, and it is strictly forbidden to grind the putty in the paint room.
▶ Ensure the cleanliness of the compressed air and replace the filter regularly. Before spraying, use compressed air or a dust cloth to clean the spraying surface.
▶ Properly seal and store the paint. The paint should be fully stirred before spraying and filtered before use.
▶ If there are already dust spots, grind to a smooth surface and then repaint. For minor dust spots, use fine sandpaper to grind and polish.
4. Feather edge cracking
The paint film cracks around the feather edge, which will appear very soon after the topcoat is sprayed.
① Cause
▶ Excessive dilution or use of inferior thinner.
▶ Too coarse sandpaper was used when grinding the bevel edge, and there was no proper treatment before painting. The solvent in the paint entered the sandpaper trace and eroded the paint film.
▶ The topcoat sprayed on the inner coating was too thick or too wet, and the solvent in the paint did not have enough time to evaporate outward.
▶ The old paint film or previously repaired defects appeared, or too much atomic putty was used.
② Correction method
▶ Correctly grind the feather edge, transition smoothly and smoothly, and avoid any sharp corners and layers.
▶ Use thinner as required and use the correct dilution ratio according to the specific conditions of the workshop.
▶ Do not blow dry the sprayed paint film with air, because this can only achieve surface drying.
▶ When cracking occurs, the paint film surface should be polished and re-sprayed.
5. Streaks
Are also called silver powder blooming, which is a common problem of silver powder and pearl primer. The paint film shows traces of being knocked, with some dark circles surrounding light silver powder or different shades of color. If it is in the base paint, this phenomenon is often discovered after spraying the varnish.
① Cause
▶ Silver powder paint is composed of various pigments and aluminum powder. Spraying silver powder paint on a thick or wet paint surface will prevent the silver powder in the silver powder paint from flowing flat, thus forming streaks.
▶ When the temperature is too low and silver powder paint is sprayed, the silver powder will be in a wet or liquid state for a long time, causing the silver powder to accumulate in piles.
▶ When spraying silver powder paint, if the air pressure used is low, or the distance between the spray gun and the surface plate is close, when the paint surface reaches the working surface, the solvent in it will evaporate too little, resulting in the formation of a wet paint film, which is easy to cause streaks.
▶ A thinner with a very slow evaporation rate was used, or the thinner was used in excessive amounts.
② Correction method
▶ Dilute the silver paint as required and master the correct spraying techniques, such as the distance between the spray gun and the spraying surface and the movement speed of the spray gun.
▶ Do not apply wet paint too thickly. If necessary, appropriately increase the temperature of the spray shop and appropriately extend the standing time between paint films.
▶ If streaks have already occurred, it is recommended to re-spray using the correct dilution ratio and construction techniques. If streaks occur in the base paint sprayed with clear varnish, the paint film needs to be peeled off and re-sprayed.
