The specialist’s guide – Mistakes while painting

Gathering


Definition:
Lifting or swelling (creping) of the freshly applied layer.
Causes:
1. Too long drying time to touch when working with applicable wet-on-wet products (if the application time of the second layer specified in the technical data sheets is not respected).
2. Repainting of solvent-sensitive paints (TPA-acrylic thermoplastics) with unproper products.
3. Paints are applied in too thin layers.

How to avoid:
1. Always follow the recommended drying times (do not leave the products to dry too much).
2. Do a solvent test before application and use the appropriate materials at the recommended layer thickness.
3. Apply the products in the recommended layer thickness.

Sweating


Definition:
Slow evaporation of the solvent (sweat) from the freshly applied paint layer.
This leads to “sweating” of the paint layer, which leads to reduced gloss or spots with different types of gloss.
Causes:
1. Insufficient drying between coats ot the application of too thick layers.
2. Soaking and swelling of solvent sensitive substrates.
3. Adding the wrong amount of hardener and / or solvent in two component products.
How to avoid:
1. Always observe the recommended layer thickness and recommended drying times.
2. Do a solvent test before application. Apply the products in the recommended thickness, with aeration time between coats in order to create an insulation from the solvent sensitive substrate. Do not apply putty on old solvent-sensitive paint.
3. Observe the mixing ratios.
Remedy:
Sand the entire affected area and rebuild the system with suitable products.

Blistering


Definition:
In wet weather, a small amount of vapor is absorbed into the paint layer and then evaporated during the drying process.
In such situations, if humidity is not controlled, salts can remain after drying. These salts cause a local concentration of salt solution that will penetrate the paint layer subsequently applied in the form of blisters. These blisters can appear in different sizes and locations, either on certain areas or in the entire paint film.
Causes:
1. The surface to be painted has not been sufficiently cleaned. Contamination with salt residues, sweat from the hand, dirty water from grinding on wet were left on the paint surface or between layers.
2. Wet sanding operations without enough time left to evaporate the water before applying the paint.
3. Climatic conditions in the painting booth during painting.
How to avoid:
1. Thoroughly clean the surface before painting with clean water. Try to sand as much as possible on “dry”.
2. Allow enough time for the water to evaporate (approx. 2 hours at 20ºC) when sanding. Sand as much as possible, especially polyester putties.
3. Make sure the paint booth is dry before painting.
In cold and wet weather, place the cabin on the drying cycle shortly before the start of painting.
Remedy:
Sand and completely remove the defect to the layer in which it appeared. Then redo the entire painting system.

Poor coverage


Definition:
The substrate is visible through the layer of applied paint.
Causes:
1. The applied paint was over-diluted.
2. The layers of the applied paint is too thin.
3. The products was not mixed enough.
How to avoid:
1. Observe the dilution ratios.
3. Apply the paint in the recommended layer thickness.
4. Mix the product well before preparing the paint.

Remedy:
After drying, sand and repaint.
Low gloss

Causes:
1. Slow evaporation of the solvent from the previous coat of paint.
2. Applying the paint in too thick layers.
3. Atmospheric factors – the action of sulfur dioxide, nitrogen oxide in combination with atmospheric humidity or UV radiation.
4. Incorrect amount of hardener in 2k, 3k paints.
5. Incorrect treatment after painting:

  1. Washing with very rough or used brushes.
  2. Aggressive washing liquid.

6. Removing the painted parts too early in the environment. Freshly applied paint in too thick layers is sensitive to moisture in the air.
7. Insufficient ventilation during painting or drying.

How to avoid:
1. See “sweating”.
2. Apply the paint in the recommended layer thickness.
3. Pay attention to atmospheric factors.
4. Observe the mixing ratios.
5. Observe the drying times and the recommended layer thickness.
7. Check the air circulation in the paint booth and the booth filters.
Remedy:
Repaint.

Poor adherence


Poor adherence can be manifested in 2 ways:
1. Either the whole system detaches
2. Poor adhesion is manifested only between layers.
Causes:
1. Substances that can cause poor adhesion are left on the surface (silicone, oil, grease, protective wax).
2. Applying an inappropriate primer or filler.
3. Insufficient sanding on the surface.
4. The primer or paint was applied in too thin layers.
5. Drying in defective conditions.
How to avoid:
To avoid lack of adhesion on the substrate, observe the following:
1. Use a primer or filler indicated for the substrate.
2. Apply the products according to the technical instructions.
3. Clean and degrease surfaces before applying any product.
Remedy:
Completely remove the low-adhesion layers. Sand and degrease the surface.
Repaint using suitable products.

Solvent bubbles


Definition:
Small bubbles that appeared due to the penetration of the solvent from the lower layer to the upper one.
Causes:
1. Coats applied too thick.
2. Hardener or thinner too fast.
3. Aeration time too short when using products with wet-on-wet application.

How to avoid:
1. Observe the recommended layer thickness.
2. Use the recommended hardener and thinner depending on the working temperature.
3. Leave the recommended aeration times between layers.

Remedy:
To repair this defect, it must be sanded to the layer in which they appeared and then repainted. If these small bubbles are not completely removed, they will lead to stings when the next coat of paint is applied.

Stings


Definition:
Small stings 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 sand and remove the bubbles or cover them.
Remedy:
The stings are repaired by sanding the surface or filling them by applying fillers.

Craters

Definition:
Circular craters with a diameter from 0.5 mm to 3 mm.
Causes:
The main cause is the presence on the surface of substances such as oil, grease, wax or silicone.
These substances may come from:
1. Personal – stains on work cloths, marks on gloves, hair lotions, sweating.
2. Painting cabin – Lubricating oils from certain components, substances for treating plastic parts, insulation, dirt on the cabin floor.
3. Paint – Incorrect use of additives, impurities in transport or storage.
4. Part – Residues from plastic parts treatment agents, oil from insulating products, welding fumes.
5. Tools and auxiliary products – Unproper degreaser, masking tape adhesives.
6. Environment – Exhaust fumes, welding fumes, dust from building insulation materials.
How to avoid:
Use in and near the paint only silicone-free products and cleaning /degreasing the surfaces to be painted.
Remedy:
Sand to the layer where the crater appeared and repaint.

Chalking


Definition:
Decomposition of binders on the painted surface which leads to discoloration of the pigments in the paint and the appearance of a fine and dusty power at the surface of the paint.
Causes:
1. The used paint does not resist to UV (eg. epoxy products)
2. Using an unproper hardener or in the wrong amount.
3. The paint layer applied in too thick layers.
4. The action of external factors (pollution with sulfur dioxide or nitrogen oxides in combination with high humidity).
5. Incomplete repair of a previous chalking.
How to avoid:
1. Use painting systems where the last layer has UV resistance properties.
2. Always use the hardeners indicated in the recommended quantities.
3. Apply the paint in the recommended layer thickness.
4. Make sure that the previous discoloration has been completely removed by sanding to the layer where 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 to the layer in which it appeared and then repainted.

Peeling of the paint


Definition:
Total removal of the entire paint film.
Causes:
1. Incomplete cleaning of the substrate.
2. Insufficient sanding to create adhesion.
3. Using an unsuitable degreaser.
How to avoid:
1. Proper preparation of the surface (rust removal, dedusting, degreasing)
2. Always sand with the recommended abrasive before application.
3. Use the indicated degreaser.
4. Always use primer or DTM to have the necessary properties of adhesion to the surface to be painted.
Remedy:
Remove all peeling paint completely and repaint the entire system accordingly.

Cracks


Definition:
Cracks or breaks in the form of a line in the paint layer.
Causes:
1. The application of the paint was not made correctly.
2. The thickness of the entire paint system is too large.
How to avoid:
1. Keep the recommended layer thickness for each product.
Remedy:
If possible, remove the paint by sanding and then redo the paint system.

Leakage


Definition:
Spills of freshly applied paint.
Causes:
1. The viscosity of the paint is too low.
2. The piece to be painted is too cold (it was not air-conditioned before painting).
3. Paint applied too thick.
4. Too many layers applied.
5. Aeration time between layers too short.
6. Painting distance too short.
7. The nozzle of the gun used is too large.
8. Defective painting technique.
How to avoid:
1. Maintain the application viscosity.
2. Observe the painting distance as well as the nozzle indicated for each product.
Remedy:
Leak removal is done by grinding with 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:
1. The pigment in the prepared paint does not have the same composition as in the paint on the object to be painted.
2. Preparing a paint that differs from the one in the recipe without checking the color under various light sources.
3. Shading the paint applied with a paste that is not in the original recipe.
How to avoid:
1. When preparing a new shade that is not in the recipe, metamerism must be verified by colorimetric tests and measurements.
2. For colors that are in the recipe they must be checked in various light sources.
3. Make colors 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 like that of an orange peel.
Causes:
1. Painting distance too long.
2. Paint pressure too low.
3. Layer thickness too small.
4. The viscosity of the paint is too high.
5. The hardener and / or thinner used is too fast for the application conditions and for the size of the surface to be painted.
6. Gun nozzle too small.
7. Too long time between layers.
How to avoid:
1. Keep the recommended painting distance.
2. Paint at the indicated pressure.
3. Always apply solid coats.
4. Maintain the recommended application viscosity.
5. Choose the right hardener for the painting conditions and the size of the parts to be painted.
6. Use the recommended gun nozzle.
7. Allow the recommended aeration times.
Remedy:
If the defect is major, sand the surface and then repaint.

Margins (contours)


Definition:
Contouring the edges visible in the final paint around the surfaces where putty was applied.
Causes:
1. Insufficient drying of the putty.
2. Soaking the layer applied on the meeting area where the filler layer met the old paint on the machine or sheet. Or the lost sanding of the edges was not done properly.
3. Unproper paint system applied over TPA (acrylic thermoplastic) or NC (nitrocellulose) paints.
4. Surfaces sanded to the sheet not properly insulated before applying paint and varnish.
5. Polyester putty applied over the old paint in a thick layer.
How to avoid:
1. Observe the recommended drying times.
2. 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 grinding, make sure that you have observed the grinding granules for grinding the substrate
4. Build a suitable painting system: putty-filler-paint-varnish.
5. Do not apply polyester putty in thick layers on the old paint. Apply putty only on clean surfaces.
Remedy:
Sand the respective surface and repaint accordingly.

Folding, shriveled appearance


Definition:
The surface of the applied paint is textured, with irregularities. This defect occurs when the final paint dries faster than those applied under it. It usually occurs in the presence of synthetic enamels.
Causes:
1. Synthetic enamel applied too thick.
2. Unfavorable drying conditions (temperature too high).
How to avoid:
1. Observe the recommended number of layers and the recommended film thickness.
2. Dry at optimum temperature, not too high.
Remedy:
For small defects, dry the painted surface properly, sand to the perfectly hardened substrate and then repaint.
For major defects, strip the entire paint system and repair properly.

Dust inclusions


Definition:
Small particles of various origins (dust, lint) present in the paint film.
Causes:
1. The substrate has not been cleaned before painting.
2. The filter system of the paint booth is dirty, dirty air supply hoses etc.
3. Contamination of the finishing areas with air from the preparation areas.
How to avoid:
1. Degrease and clean before painting.
2. Ensure proper maintenance of the painting booth.
3. Make sure that the finishing areas of the paint are separated from the preparation areas.
Remedy:
For minor defects, polish.
For major defects, sand to the layer where the contamination originated and repaint.

Gassing


Definition:
Gases from the paint that will reach the parts next to the painted one or that are not absorbed by the previously applied paint.
Causes:
1. 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.
2. Defective painting technique.
How to avoid:
1. Select the appropriate hardener and thinner for the temperature of the environment in which it is painted and for the size of the painted surface.
2. Use the recommended painting technique.
Remedy:
The surfaces must be lightly polished.

Solvent test


Before starting any operation on a surface with old paint, we recommend making a SOLVENT TEST, to check if the existing paint system contains solvent-sensitive paints, and therefore the need for proper treatment.
Solvent sensitive paints:
1. Thermoplastic Acrylics (TPA);
2. Nitro cellulose;
3. Totally unreinforced paints;
4. Paints that show the defect of slow evaporation of the solvents in the component.
How to do the test:
Sand a small portion of the part to be repaired so that all layers of the system are identified.
Soak a cloth in a strong solvent or in the solvent you want to identify and insist on the sanded surface. Carefully analyze it and if you observe that a layer softens, rises or becomes sticky, then that layer is sensitive to solvent.
Instructions for treating a surface with solvent-sensitive paint:
• The grinding operation must be done with a much finer abrasive than usual and on a much larger surface.
• Where the solvent-sensitive system is thick and highly reactive to the solvent, it must be completely removed to the clean sheet before starting the repair operation.

Rust

Definition:
Deterioration of the paint state in the form of irregular swellings. If the swollen paint is removed, rust on the metal or white rust on the aluminum can be seen underneath.
Causes:
1. Mechanical damage to the paint film that caused moisture to penetrate under the paint film, causing rust to appear on the metal substrate.
2. Poor preparation and cleaning of the metal substrate before painting.
3. Fresh rust on freshly sandblasted surfaces.
How to avoid:
1. Scratches or bumps must be repaired immediately.
2. Ensure proper cleaning of the metal surface before painting (degreaser).
3. Sandblasted surfaces should be primed immediately after sandblasting, no later than 3-4 hours.
Remedy:
Remove all paint from the affected area and rust underneath, by sanding, sandblasting etc. Clean the surface of any traces of rust, grease etc. with degreaser. Apply a layer of primer as quickly as possible on the clean metal surface to avoid rust and then start applying the following products (paint, enamel, lacquer).