FREQUENT DEFECTS IN PAINTING
Increasing
Definition:
Lifting or swelling (creasing) of the freshly applied layer.Causes:
Too long drying time when working with wet-on-wet products. Repainting some solvent-sensitive paints (TPA-acrylic thermoplastics) with non-indicated products. Paints applied as insulators are applied in too thin layers or are sanded too deeply.How to avoid:
Always respect the recommended cooling times (don’t leave too long). Do a solvent test before application and use the appropriate materials for the recommended layer thickness. Apply the products to the recommended layer thickness.Sweating
Definition:
The slow evaporation of the solvent (sweats) from the freshly applied paint layer. This leads to perspiration of the paint layer, which leads to reduced gloss or contours.Causes:
Insufficient drying between layers in the case of complete painting or the application of filler in too thick layers. Application of loading or filling materials in too thick layers. Softening and swelling of substrates sensitive to solvents. Adding the wrong amount of hardener to the putty or filler.How to avoid:
Always respect the recommended layer thickness and the recommended drying times. Do a solvent test before application. Apply the filler in normal layers with air time between layers to create an isolation from the solvent-sensitive substrate. Do not apply putty to old solvent-sensitive paint. Respect the mixing rations.Remedy:
Sand the entire affected area and rebuild the system with suitable products.Basic
Definition:
In wet weather, a small amount of vapor is absorbed into the paint layer and then evaporates during the drying process. Defective processing of the filler will leave salts on the surface. These salts cause a local concentration of salt solution that will penetrate the paint layer later applied in the form of basicutes. These chips can appear in different sizes and locations, either on certain areas or in the entire paint film.Causes:
The surface to be painted (filler, sheet, etc.) was not sufficiently cleaned. Contamination with salt residues, hand sweat, dirty water from wet sanding, were left on the surface to be painted or between layers. Wet sanding operations without sufficient time left for the water to evaporate before applying the paint. Climatic conditions in the painting booth during painting.How to avoid:
Clean the surface well before painting with clean water. Change the water regularly during wet sanding. Try to sand as dry as possible. Allow enough time for the water to evaporate (approx. 2 hours at 20ºC) when sanding wet. Dry sand as much as possible, especially polyester putties. Make sure that the paint booth is dry before painting. In cold and wet weather, put the cabin on the drying cycle shortly before starting painting.Remedy:
Sand and completely remove the defect up to the layer in which it appeared. Then redo the entire painting system (primer, filler, paint).Bleeding, staining
Definition:
Bleeding is the staining or bleeding of a dye from the previous substrate into the upper paint layer. It is observed as a stain or discoloration in the paint layer (often red or yellow). The excess of peroxide hardener in polyester putty can cause this defect due to the reaction with the pigments in the paint.Causes:
The soluble pigments or dyes in the old paint are dissolved by the solvent in the new paint. Staining can occur when the excess peroxide hardener from the polyester products reacts with the pigments from the other products, leading to the appearance of yellow-brown stains. Blue and green colors are especially vulnerable to this phenomenon. Bitumen or tar residues on the surface.How to avoid:
Perform a solvent test on the old paint to check for soluble pigments. Always respect the mixing ratios indicated for the mixture with the hardener and mix until complete homogenization with the putty. Before painting, make sure that the surface is cleaned of possible contamination with bitumen or tar.Remedy:
To fix such a defect, the respective surface must be insulated with an intermediate product applied as an insulator. If the stain is deep, the surface must be sanded down to the substrate where it appeared and the entire system repainted with suitable materials.Weak coverage
Definition:
The substrate is visible through the layer of applied paint.Causes:
For certain shades, the indicated colored intermediate layer (undercoat) was not applied. The applied paint was over diluted. Paint applied in too thin layers. Basic colors not mixed enough.How to avoid:
Always apply the colored intermediate layer (undercoat) indicated in the recipe. Respect the dilution ratios. Apply the paint in the recommended layer thickness. Mix the base colors before preparing the paint.Remedy:
After drying, it is sanded and repainted.Low Gloss
Causes:
Slow evaporation of the solvent from the previous paint layer. Applying paint in too thick layers. Atmospheric factors – the action of sulfur dioxide, nitrogen oxide in combination with atmospheric humidity or UV radiation. Incorrect amount of hardener in 2k paints.Incorrect treatment after painting:
Incorrect polishing (too aggressive polish or polish in the sun). Washing with very rough or worn brushes. Aggressive washing liquid. Removing the painted car too early in the ambient environment. Fresh paint applied in too thick layers is sensitive to the humidity in the air. Insufficient ventilation during painting or during drying.How to avoid:
See „low evaporation”. Apply the paint in the recommended layer thickness. Pay attention to atmospheric factors. Respect the mixing rations. See the chapter „After painting”. Observe the recommended drying times and layer thickness. Check the air circulation in the paint booth and the cabin filters.Remedy:
Try to polish the respective area. If it doesn’t help, it will be repainted.Weak adhesion
Definition:
Weak adhesion can manifest itself in 2 ways: Either the whole system falls apart; Weak adhesion is manifested only between layers.Causes:
Substances that can cause poor adhesion are left on the surface (silicone, oil, fats, protective wax). Applying an inappropriate primer or filler. Insufficient sanding on the surface. The primer or paint were applied in too thin layers. Drying in defective conditions.How to avoid:
To avoid lack of adhesion to the substrate, observe the following: Use a primer or filler indicated for the respective substrate. Apply the products according to the technical instructions. Clean and degrease the surfaces before any product application.Remedy:
Completely remove the layers with low adhesion. Sand and degrease the surface. Repaint using appropriate products.Solvent bubbles
Definition:
Cracks due to the penetration of the solvent from the lower layer into the upper one.Causes:
Layers applied too thickly. Hardener or thinner too fast. Aeration time between layers too short. Drying time before drying with the infrared lamp is too long. Insufficient distance between the painted object and the IR lamp. Aeration time too short when using wet-on-wet application products.How to avoid:
Observe the recommended layer thickness. Use the recommended hardener and thinner depending on the working temperature. Leave the recommended airing times between layers. Leave the recommended airing times before drying with IR. Keep the recommended distance from the piece when drying with IR. Leave the recommended airing times between layers.Remedy:
To remedy this defect, it must be sanded down to the layer in which they appeared and then repainted. If these small bubbles are not completely removed, they will lead to the appearance of pitting when the next layer of paint is applied.Stings
Definition:
Small pits or craters in the freshly applied paint as a result of solvent bubbles not completely removed from the old paint.Causes:
Solvent bubbles present in the substrate on which the paint is applied.How to avoid:
Either they are sanded and the bubbles are removed, or they are plugged.Remedy:
Punctures are repaired by sanding the surface or filling them by applying some filling products.Crater
Definition:
Circular craters with a diameter from 0.5 mm to 3 mm.Causes:
The main cause is the presence of substances on the surface such as: oil, fat, wax or silicone.These substances can come from:
Personal – stains on work cloths, traces on gloves, hair lotions, perspiration. Paint booth – Lubricating oils from certain components, substances for treating plastic parts, insulators, dirt on the booth floor. Paint – Incorrect use of anti-silicone additives, impurities from transport or storage. Part – Residues from plastic parts treatment agents, oil from welding fume insulating products. Tools and auxiliary products – Inappropriate degreaser, masking tape adhesives. Ambient environment – Exhaust gases, welding fumes, dust from insulating construction materials.How to avoid:
Using only silicone-free products in and near the paint shop and cleaning and degreasing the surfaces to be painted.Remedy:
Sanding up to the layer where the crater appeared and repainting.Scratches from washing brushes
Definition:
Traces of parallel scratches visible especially on dark colors. The surface can also lose its gloss.Causes:
Manual or automatic washing with too rough or very worn brushes. Prewash too dry or with too little water. Washing the car too quickly after it has been painted.How to avoid:
Use normal brushes for washing the car. Water the car abundantly before washing. Avoid washing the car immediately after painting.Remedy:
Polish the scratches with abrasive polish and then with gloss polish.Creating
Definition:
The decomposition of the binders in the painted surface leads to the discoloration of the paint pigments, so that the red and yellow colors become whitish, and the blue becomes bronze.Causes:
Using an inappropriate hardener or in the wrong amount. The paint layer applied in too thick layers. The action of external factors (pollution with sulfur dioxide or nitrogen oxides in combination with high humidity). Defective treatment after painting. Incomplete repair of a previous chalking.How to avoid:
Always use the indicated strengtheners in the recommended quantities. Apply the paint in the recommended layer thickness. Protect the car from harmful external factors. Do not subject freshly painted surfaces to harsh treatments. Make sure that the previous chalking has been completely removed by sanding down to the layer in which it appeared.Remedy:
Try to polish the affected surface with abrasive polish and then with gloss polish. If it does not help or if the defect reappears after a few weeks, then it must be removed by sanding up to the layer in which it appeared and then repainted.Paint peeling
Definition:
Total removal of the entire paint film.Causes:
Incomplete cleaning of the plastic substrate. Insufficient sanding to create adhesion. Using an inappropriate degreaser. The plastic part was not tempered before painting. No adhesion primer was used.How to avoid:
Wash the piece with water and detergent to remove substances that are only soluble in water. Then degrease with degreaser to remove solvent-soluble contamination. Always sand with the recommended abrasive before application. Use the indicated degreaser. Tempering is the operation of „removing” the substances from the plastic pores by heating (1-2 hours at 60º C). The plastic parts with a porous surface must be tempered to remove from the plastic the „treating agents that entered the pores of the plastic during the treatment operation. This problem can occur with PUR plastics. Clean the plastic with degreaser before and after tempering. Always use plastic adhesion primer.Remedy:
Remove all peeling paint completely and repaint the entire system accordingly. Do not use solvent to remove the paint. This solvent can destroy the plastic.Cracks
Definition:
Cracks or breaks in the form of a line in the paint layer.Causes:
No elasticizing additive was added to the paint applied to the spoiler. The thickness of the entire paint system is too high.How to avoid:
Use an elasticizing additive when applying plastic paint (see technical sheet). Keep the recommended layer thickness for each product.Remedy:
Remove, if possible, by sanding, the paint and then redo the painting system. Do not remove the paint from the plastic parts with the help of aggressive solvents (it can destroy the plastic).Pigs (pores)
Definition:
Small holes in the painted surface due to the pores on the plastic surface.Causes:
Defects in the manufacture of plastic parts.How to avoid:
Check very carefully the surface of the plastic parts before painting.Leaks
Definition:
Leaks of freshly applied paint.Causes:
Paint viscosity too low. The part to be painted is too cold (it was not conditioned before painting). The paint was applied too thickly. Too many layers applied. Aeration time between layers too short. Painting distance too short. The nozzle of the gun used is too large. Defective painting technique.How to avoid:
Keep the application viscosity. Apply the paint on parts that have been conditioned (the part has the temperature of the environment). Respect the painting distance as well as the nozzle indicated for each product.Remedy:
The removal of leaks is done by sanding with a very fine abrasive or by polishing.Metamerism
Definition:
It is an effect in which a color can appear in various shades in various light conditions. The most common case is when two colors match in daylight, but are different in artificial light.Causes:
The pigment in the prepared paint does not have the same composition as the paint on the car. Preparing a paint that differs from the one in the recipe without checking the color under various light sources. Tinting the paint applied with a paste that is not in the original recipe.How to avoid:
When preparing a new shade that is not in the recipe, the metamerism must be checked through colorimetric tests and measurements. For shades that are in the recipe, they must be checked in various light sources. Make shades only with the pasta in the recipe.Remedy:
Small metamerism effects can be solved by the blend-in or loss technique.Orange peel
Definition:
The appearance of the paint on the surface is similar to that of an orange peel.Causes:
Far too long painting distance. Painting pressure too low. Layer thickness too small. The viscosity of the paint is too high (the paint is too diluted). The hardener and/or thinner used are too fast for the application conditions and for the size of the surface to be painted. Gun nozzle too small. Too long drying time between layers.How to avoid:
Keep the recommended distance from painting. Paint at the indicated pressure. Always apply full coats. Keep the recommended application viscosity. Choose the right hardener for the painting conditions and the size of the parts to be painted. Use the recommended gun nozzle. Leave the recommended aeration times.Remedy:
If the defect is minor, polish the surface. If the defect is major, sand the surface and then repaint.Borders (outlines)
Definition:
Edge contouring visible in the final paint around the surfaces where putty or filler has been applied.Causes:
Insufficient drying of the filler or putty. Softening the layer applied to the meeting area where the filler layer met the old paint on the car or sheet. Or the lost sanding of the edges was not done properly. Improper paint system applied over TPA (thermoplastic acrylic) or NC (nitrocellulosic) paints. Surfaces sanded down to sheet metal not properly insulated before applying paint and varnish. Polyester putty applied over the old paint in a thick layer.How to avoid:
Respect the recommended drying times. Drying with IR lamps reduces the risk of contouring due to the drying method (from the sheet to the last layer). Before starting the repair, do a solvent test (with an acrylic or nitro solvent) to check the sensitivity of the old paint to solvents. When sanding, make sure that you have respected the sanding granulations for sanding the substrate before applying the following product: P80/150-for putty. P240-for.primer/filler. Apply the solvent-free filler layer in a thin layer to isolate solvent-sensitive surfaces. Build a suitable painting system: putty-filler-paint-varnish. Do not apply polyester putty in thick layers on the old paint. Apply putty only to the clean board and leave a clean edge of the board up to the old paint.Remedy:
The respective surface is sanded and repainted accordingly.Cracks (crocodile skin look)
Definition:
Cracks of various lengths, depths and widths.Causes:
The use of polyester putties, washprimers, synthetic enamels directly on TPA (thermoplastic acrylic) paints. No hardener has been added to 2k products. Application of polyester putty over washprimer primer. Too aggressive drying with UV lamps, large temperature fluctuations. Aeration times too short when applying wet-on-wet products. The film thickness of the entire applied system is too high.How to avoid:
Do not apply polyester putties or reactive washprimer primers over TPA paints. Observe the mixing ratios for the 2k products. Do not apply polyester putty over washprimer reactive primer. Follow the instructions for use of the UV lamps. Leave the recommended aeration times. Observe the recommended film thickness.Remedy:
The respective surface is sanded down to the substrate where the defect no longer appears and the corresponding system is restored.Cutting, scrolling
Definition:
The surface of the applied paint is textured, with irregularities. This defect occurs when the final paint dries faster than the ones applied below it. It usually appears in the presence of synthetic enamels.Causes:
Synthetic enamel applied too thick. No drying solution was added to the synthetic enamel. Unfavorable drying conditions (temperature too high).How to avoid:
Observe the recommended number of layers and the recommended film thickness. Make sure that the drying solution will be added to the recipe. Dry at the optimal temperature, not too high.Remedy:
For small defects, dry the painted surface properly, sand until the substrate is perfectly hardened and then repaint. For large defects, the entire paint system is stripped and redone accordingly.Sanding marks, sanding scratches
Definition:
Traces of sanding from the previous substrate.Causes:
The previous substrate was sanded too coarsely. The scratch thus formed is too deep to be covered by the product applied over it. The drying times of the primer or filler were not respected. Thus, the sanding marks will become visible during the application of the final paint due to the softening of the filler layer, and then surface creasing will appear during drying. The filler layer was applied too thin to cover the scratches. Failure to follow the sanding steps or a faulty sanding technique.How to avoid:
Follow the sequence of sanding steps. Respect the drying times. Respect the layer thicknesses. Always place the sole of the sander on the workpiece and then turn on the sander.Remedy:
Sand down to the substrate where the scratches appeared and repaint again.Dust inclusions
Definition:
Small particles of various origins (dust, fluff) present in the paint film.Causes:
The substrate was not cleaned before painting. The filter system of the paint booth is dirty, the air supply hoses are dirty, etc. Contamination of finishing areas with air from preparation areas.How to avoid:
Degrease and clean before painting. Ensure the correct maintenance of the paint booth. Make sure that the finishing areas of the paint are separated from the preparation areas.Remedy:
For minor defects it is polished. For major defects, sand down to the layer where the contamination originates and repaint.Gasification
Definition:
Gases from painting that will reach the parts attached to the painted one or that are not absorbed by the previously applied paint.Causes:
Gases are not absorbed in the previous layer due to the use of a hardener or thinner too fast for the painting conditions or too fast for the size of the painted surfaces. Defective painting technique.How to avoid:
Select the right hardener and thinner for the temperature of the environment in which it is painted and for the size of the painted surface. Use the recommended painting technique.Remedy:
It is polished first with an abrasive polish and then with a gloss one.Stone strikes
Definition:
Mechanical damages in the paint layer due to stone hits on the road.Causes:
Hitting stones of various sizes from the roadway. Depending on the force with which these stones hit the paint system, damages may appear in the paint layer or in the primer-filler layer up to the clean sheet. The moisture will penetrate the paint film and detachments of the entire paint system may occur.How to avoid:
There is no total protection against stone blows. For the surfaces that are more exposed to these impacts, the paint is added with an elasticizing additive to increase the elasticity of the film.Remedy:
The entire affected area is sanded down to the product that did not jump off the support and the appropriate painting system is restored.Water marks
Definition:
Traces of water appear as small circular whitish spots, resulting from the evaporation of water in combination with mineral salts on the paint film. The surface inside the stain is almost intact, while the outer edge of the stain is slightly raised.Causes:
Insufficient drying of the paint before leaving the car in the rain. The hardener used was inadequate or used in insufficient quantity.How to avoid:
Make sure that the paint is applied to the required thickness (no more) with the recommended amount of hardener so that it can dry properly.Remedy:
If the damage is minor, wash with clean water. If it is not repaired, polish the damaged surface. If the defect is large, you must sand the respective area (make sure it is well dry) and repaint.Solvent test
Before starting any operation on a surface with old paint, we recommend carrying out a SOLVENT TEST, to check if the existing paint system contains solvent-sensitive paints, and for this reason the need for an appropriate treatment.Solvent sensitive paints:
Thermoplastic Acrylics (TPA); Nitro cellulose; Totally unreinforced synthetics; Paints with the defect of slow evaporation of the solvents in the component.How to take the test:
A small portion of the piece to be repaired is sanded, so as to identify all the layers of the system. Soak a cloth in a strong solvent (thinner D 20), and insist on the sanded surface. It is carefully analyzed and if it is observed that a layer softens, rises or becomes sticky, then that layer is sensitive to the solvent.Instructions for treating a surface with solvent-sensitive paint:
The sanding operation must be done with a much finer abrasive than usual and on a much larger surface. Do not apply putty on the sanded edges of the sensitive system; always leave clean metal between the putty and the old paint. Apply the filler and the final paint in thin layers, leaving long airing times between layers. Do not apply fillers or paints in a wet-on-wet system. Where the solvent-sensitive system is thick and extremely solvent-reactive, it must be completely removed to a clean sheet before starting the repair operation.Rust
Definition:
Damage to the state of the paint in the form of irregular bumps. If the swollen paint is removed, rust on metal or white rust on aluminum can be seen underneath.Causes:
Mechanical damage to the paint film that caused the penetration of moisture under the paint film, causing the appearance of rust on the metal substrate. Poor preparation and cleaning of the metal substrate before painting. Freshly appeared rust on freshly sandblasted surfaces.How to avoid:
Scratches or stone hits must be repaired immediately. Ensure adequate cleaning of the metal surface before painting (degreaser). Sandblasted surfaces must be primed immediately after sandblasting.Remedy:
Remove all the paint from the affected portion and the rust underneath, by sanding, sandblasting, etc. Clean the surface of any traces of rust, grease, etc. with a degreaser. Apply a layer of reactive primer as quickly as possible on the clean metal surface to avoid the appearance of rust and then start applying the following products (filler, paint, varnish).Clouds, shadows
Definition:
Spots, light or dark marks that can be observed in the metallic paint.Causes:
Uneven application. Airing times between layers or before varnish application are too short. Metallic base paint applied either too full or too fizzy.How to avoid:
The application must be uniform and overlap the pattern of the gun as best as possible. Respect the aeration times between layers. Observe the recommended layer thickness.Remedy:
If the clouds appear during the application of the metallic base, they will be remedied by the painting technique (even and careful application). If clouds, spots become visible after applying the varnish, then the varnish must be dried, sanded and the metallic paint correctly reapplied.