Troubleshooting Paint Defects

In the painting process, there are many issues that can arise causing surface defects in the final finish. Hopefully this blog will help you identify the problem, understand what caused the problem, and will give you the next step to repair the defect or prevent it in the future. 

Defect: Description: Cause: Remedy or Prevention:
Staining or discoloring that appears through the final finish.
  1. The original paint, Primer, or coating is unstable and is dissolving when the solvent from the new paint is sprayed and thus causing the old paint to bleed through and mix with the new color.
  2. Peroxide in the body filler is being dissolved by the solvent in the new paint.
  1. Remove the original finish that is causing the bleed.
  2. Follow the body filler manufacturer's instructions for activating body filler. (Most fillers are 2% by volume, over activating can cause many various paint defects.)
The surface of the finish displays small bubbles, bumps, or pimples that may be either isolated or in groups.
  1. Spray environment has high humidity levels. 
  2. Compressor producing water.
  3. Sweat from painter. 
  4. Moisture or contaminants trapped under the surface.
  5. Rust - Surfaced was not prepped properly.
  1. Paint a different day, or control the humidity level where the project is being done.
  2. Add an inline desiccant air filter / water separator or refrigerant drier.
  3. Wear sweat bands, coveralls, (tape around the wrist to prevent sweat from running out the sleeve), wear a spray sock to absorb sweat.
  4. Clean the surface and dry thoroughly before applying the coating.
  5. Prep substrate well and use products that are designed for bare metal.
Visible marks showing after the final paint work has been completed, specifically around the featheredge on body filler or primer edge.
  1. This is generally caused by improper surface preparation or material application.
  1. Follow the body filler and primer manufacturer's instructions for proper surface preparation, grit selection, flash times, dry times, and recoat times. Also closely monitor temperature and humidity range in the work area. To repair, the areas will have to be sanded and refinished.
Visible sanding marks after the paint work has fully cured that was not visible during the repair process or immediately following the repair.
  1. Improper mix of products.
  2. Too coarse of sandpaper or too large of a jump between grits of sandpaper.
  3. Undercoats not allowed to properly dry / flash prior to application of finish coat or applied to excessive.
  1. Mix products thoroughly as recommended by the manufacturer.
  2. Refine the grit by not jumping more than 100 at a time. (For example: Don't level filler with 36 grit and try to refine the scratch with 180 grit.)
  3. Follow the manufacturer's guidelines for dry / flash time and film thickness per coat.
Raising, cracking, or swelling of the paint film.

(Lacquer Paint over Enamel Paint will cause this. Enamel can be applied over lacquer but not the other way around.)
  1. Incompatible or unstable paint materials is often the cause. 
  2. Exceeded maximum flash / dry time of previous coat.
  3. Substrate surface not properly cleaned.
  1. Check paint compatibility prior to application.
  2. Follow the manufacturer's guidelines. Sand or strip the previous coat/s and start again.
  3. Clean thoroughly using solvent based and water based cleaners prior to painting.

Tech Tip: Quite often you can apply 2-3 coats of a water-based primer and this will prevent the solvent from penetrating into the unstable finish underneath.

Color distortion resulting from an uneven distribution of metallic, mica, or special effect pigment.
  1. Improper equipment or set-up.
  2. Incorrect Reducer.
  3. Material settled or not mixed uniformly
  4. Poor Application
  5. Uneven Spray Pattern
  6. Too hot or cold spray environment.
  1. Use recommended spray gun, tip size, and air cap recommended by the paint manufacturer.
  2. Refer to paint manufacturer's recommendations.
  3. Shake or stir well.
  4. Use proper overlap and distance recommended by the spray gun manufacturer's recommendations.
  5. Clean spray gun well.
  6. Monitor temperature of the spray environment.

Tech Tip: Choose one temperature slower than what you think you need and allow more flash time between coats.

Paint or Clear-coat with an uneven texture that resembles the skin of an orange.
  1. Improper mix, under reduced, or incorrect air pressure.
  2. Reducer selection too fast for spray condition.
  3. Excessive film thickness.
  4. Incorrect spray gun set-up and application.
  5. Viscosity of the Paint is too thick.
  1. Shake or stir well, use proper reduction ratio, and spray at the recommended pressure.
  2. Select reducer based on spray area environment and job size.
  3. Avoid heavy coats and excessive film build.
  4. Follow spray-gun manufacturer's recommendations.
  5. Reduce paint to a sprayable viscosity.

Tech Tip: Choose one temperature slower than what you think you need and allow more flash time between coats.

A dulling of the gloss as the film dries or ages.
  1. Poor application.
  2. Poor quality finish.
  3. Application over unstable finish or inferior undercoat.
  4. Slow drying due to high humidity or low temperature.
  5. Solvent fumes or exhaust gases attacking the surface.
  1. Use correct distance and spray gun speed for proper application.
  2. Use good quality products. (It is a lot of work to prep a vehicle for paint, don't ruin all that hard work and settle for cheap / inferior products.)
  3. Check the stability of existing paint prior to completing the job. If you are unsure, the recommendation is to remove the existing coating.
  4. Follow paint manufacturer's recommendation for temperature and humidity for the products you are spraying.
  5. Evacuate the exhaust air from the spray area for several hours after project is completed.

Tech Tip: Dieback can often be sanded and buffed out using progressively finer grits then compound and polish. If this does not work

Crater like depressions on the surface of the paint or clear-coat.
  1. Improper surface preparation.
  2. Spraying over a previously repaired surface where fisheye eliminator was used.
  3. Air supply was contaminated with oil, water, or both.
  4. External contaminants entering the spray environment.
  1.  Clean the surface to be painted with both water-based and solvent-based wax and grease remover.
  2. Remove the previous coating or use fisheye eliminator to complete the repair.
  3. Regularly maintenance the air compressor, air lines, and the air filtration system.
  4. Ventilate and properly filter spray area.

Tech Tip: The coating will have to be sanded until the fisheyes are gone, then follow step 1 above before more color or clear-coat can be applied.

Small bubble like  surface defects that under magnification protrude out. 
  1. Solvent entrapment that bursts through surface of the paint or clearcoat finish.
  2. Reducer / Hardener selection too fast.
  1.  Allow more flash time between coats and / or use a slower drying reducer / hardener.
  2. Choose Reducer and / or Hardener based on temperature and job size.

Tech Tip: Use one temp slower hardener / reducer than you think you might need, and allow longer flash time between coats.

  • RUNS
 The downward flow of primer, paint, or clear-coat.
  1. Improper Reduction.
  2. Spray-Gun not setup correctly.
  3. Applying materials too wet.
  4. Holding the spray-gun too close to the surface.
  5. improper Overlap.
  1.  Follow paint manufacturers recommendations.
  2. Follow the spray-gun manufacturers recommendations.
  3. Apply the material in coats allowing flash time between each coat.
  4. The spray-gun should be held 8-10 inches from the surface being sprayed.
  5. Overlap should be 30-50 percent.

Tech Tip: Depending on the severity runs and sags can often be removed by sanding off in progressively finer grits then compound and polish to a full shine.

 The clear-coat has eroded from the base-coat color and may or may not be flaking off the surface and will have a milky white appearance.
  1. Inferior or poor quality clear-coat.
  2. Not enough clear-coat applied.
  3. Too much clear-coat was removed in the wet sanding and compounding.
  4. U.V. Degradation. 
  1.  Choose a good quality clear-coat. This doesn't necessarily have to be the most expensive clear-coat on the market. Consult with a knowledgeable  automotive paint supplier for recommendations.
  2. Apply the clear-coat according to the manufacturer's instructions.
  3. Add extra clear-coat in the application process so that you have enough to sand and polish. 
  4. Ultraviolet Rays will degraded the clear-coat over time. This happens to all clear-coats eventually. Good quality clear-coats can hold up for a number of years whereas poor quality clear-coats can begin failing in as little as 6 months.
26th Apr 2022 Gary Kinsey

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