The top 10 causes of contamination in automotive refinishing

Contamination is one of the scariest words among painters. Even when you think you have done a flawless job, there is always the risk of stains, halos, or craters appearing on the coated surface when the work is finished. There can be many reasons for this, including damage caused by careless preparation, poorly maintained equipment, and dirty workshop, as well as human error.
It is often difficult to determine the cause of a defect at a glance and, therefore, to apply the most suitable correction procedure. After having described the most common coating defects, in this article we will focus on the main contaminants that can come into play during the finishing phase.

Unwashed cars before finishing

Proper vehicle washing is essential to avoid introducing contaminants into the workshop and, more specifically, into the spray booth. Particular attention should be paid to the wheels, where the greatest amounts of dirt and debris typically accumulate.

Dirt and dust in the base coat or clear coat

Dirt and dust are among the main contaminants. Dirt, for example, can enter the wet film either through airborne contamination or because the base has not been properly filtered. Also, dirt may have been drawn into the clear coat and trapped. In these cases, you will see light or dark dots on the surface, depending on the color. 

To avoid this type of contamination, make sure the booth is always clean, check the crevices to remove dust, and wear appropriate work clothing (such as an anti-static and low linting suit).

If the dirt is in the base coat, the correction procedure is to remove the dirt particles and reapply the base coat to the damaged areas. On the other hand, if the dirt is on the surface of the clear coat, sanding and polishing might work as well.

Contaminated air

Air from outside can bring in dust, dirt, insects, and other contaminants that can affect the quality of the paint and painted parts. Air filtration is often taken for granted, but it is not always effective, and filters should be inspected and replaced regularly.

But even the air inside a workshop can be contaminated as a result of the work being carried out. For example, excessive sanding, carried out in open areas rather than in contained preparation zones, can cause dust to circulate throughout the workshop and into the spray booth. To limit this, we recommend that you always enter the booth with the car and engines running.

Contaminated washing instruments

The brushes used for washing or polishing can be contaminated by dirt, impurities, oils, etc., making the preparation of the car or the parts to be polished ineffective. As we mentioned early, impurities on the surface are among the most common causes of finishing defects. 
One of the possible consequences is the hologram effect, a defect of the bodywork that appears as a set of very fine micro-scratches joined together. For this reason, contaminated washing or polishing brushes must be promptly replaced.

Blisters caused by moisture

Excessive moisture absorbed by the lower layers can lead to unpleasant blisters on the bodywork. This can be caused by a variety of factors, such as residual sanding water in the corners or edges, extreme air humidity, or the use of water-based products that have not completely evaporated.

Poor spray gun maintenance or cleaning

Spray guns should be cleaned up after the application of each color or product. Dry paint left in the gun can come off and contaminate subsequent coatings. 
In addition to contamination problems, poorly maintained spray guns can lead to uneven surfaces, stains, streaks, or poor coverage during painting. Always check with the spray gun manufacturer for proper cleaning procedures.

Negative pressure in the spray booth

If a spray booth is subjected to negative pressure (i.e., when the air being expelled is greater than the air being drawn in), the booth itself can become a giant vacuum cleaner due to the chimney effect. External dust and dirt can be sucked in through any crack and end up in the booth. To keep contaminants out, booths should be balanced to operate at a slightly positive pressure compared to their surroundings.
Spray booth walls should be protected with special white non-woven adhesive films that protect the surfaces by capturing dirt and any overspray, keep the application area bright at all times and significantly reduce spray booth maintenance.

Human contamination

Inappropriate clothing represents one of the most common contamination risks. Most contaminants come from dirt that falls off clothing or skin.

To prevent contamination from affecting paint operations, painters should wear full anti-static suits, gloves, and masks. Some bodyshops are equipped with special preparation zones, installed just before entering the booth, where compressed air blowers remove any impurities from the overalls. In addition, many hair products, including shampoos, conditioners, and perfumes, can cause halos in the paint.
It should be remembered that all PPE should only be worn in the spray booth and mixing room.


If silicone is used in the workshop, for example in spray form as a lubricant, it can remain in the air for a long time and cause costly silicone contamination.
The presence of silicone in sanding and polishing dust can cause coating defects known as “crackings” that open up to reveal the substrate. The circular craters vary in diameter from 0.5mm to 3mm. They are usually visible during the application or immediately afterward.

Oil or grease

Another cause of cracking can be the presence of grease on the substrate or in the spray system. There are several products responsible for leaving oily residues on the surface, for example polishing agents and sprays.

In conclusion, many contaminations can simply be avoided through effective cleaning procedures of the parts to be painted, the system, or the working environment. Maintenance and error prevention can save a lot of time and money than having to resort to last-minute fixes.

The most common paint defects in a body shop

Painting mistakes are everyone’s nightmare in a body shop. No matter how careful you are and how much experience you have, problems such as cracking, orange peel, dripping, peeling or poor coverage are always around the corner. The causes of these coating defects can be many and often add up to one another. The good news is that nothing is irreparable and, with some good advice and the right technology, you can even minimize the imperfections.

1. Cracking

Also called wrinkling, this defect consists of a series of more or less obvious cracks in the paint layer(s). The result is just like that of cracked skin.

Essentially, the cause is the different tension between the layers, which can be caused by an incorrect choice of hardeners and/or thinners, excessive use of hardeners, incorrect mixture ratio, extreme paint thickness, or rigidity of the surface product compared to the underlying layer.

In addition to the correct choice of products, such errors can be avoided also by taking into consideration the regulation of the spray booth – mainly temperature and humidity – and the right application times and quantities of the products. 

2. Orange Peel Effect

This common paint defect is easy to recognize: the surface presents small, relatively deep holes, like the skin of an orange. 

Orange peel is typically the result of improper painting technique and is caused by the incorrect choice of hardener, the quick evaporation of thinner or human errors in the painting process (incorrect spraying distance, insufficient pressure that causes poor atomization, wrong temperature of the product or poorly sized nozzle).

3. Dripping

Another common coating defect is dripping, which appears like paint thickening forming undulations similar to sea waves on one or more points of the bodywork. Causes may involve the painter, the products, or environmental parameters.

The painter may create drips due to different thicknesses on the surface. Incorrect distance from the metal surface and non-symmetrical movements are other possible errors. 

In case of widespread dripping defects, the quality of the thinner must be taken into consideration. If the thinner is always the same, there may be a problem with the concentration. 

4. Peeling

Like the cosmetic treatment of exfoliation, peeling is a phenomenon whereby layers of paint peel away from the one underneath. Usually, the main cause is incorrect surface preparation, particularly with regard to sanding or degreasing. However, the choice of products, hardeners, or thinners that are not suitable for the substrate can also cause the paint to peel off the bodywork. In some cases, a too-wet or too-dry paint application can also cause this long-term coating defect.

5. Poor Coverage 

The defect of poor coverage is found when, although the thickness applied is sufficient, the paint does not mask the color of the base or the substrate, leaving evident stains. This coating defect should not be confused with opacity, but the reasons may be the same.

The incorrect choice of hardeners and thinners, the wrong temperature of the paint or the substrate, and working with a wrong-sized nozzle can be among the causes.

Thanks to EPS (Easy Paint System) 2.0, you can reduce the incidence of all these defects in the bodywork coating processes. EPS 2.0 is the application software to aid painting developed in collaboration with manufacturers. By answering simple questions about materials and products, the system suggests the most efficient process in real time, independently setting the right times and temperatures.

How to make a spray booth efficient

For many companies, purchasing a painting system is a real investment in the future. Ensuring the efficiency and longevity of the equipment is of paramount importance to recoup initial and ongoing costs and maximize production capacity. A spray booth performing to the highest standards throughout its entire lifecycle can make all the difference when it comes to the balance of a body shop.

How to make a spray booth efficient

There are several strategies for making a spray booth more efficient and preventing possible malfunctions. Maintenance and proper software updates are two central aspects, but they are not the only ones.

Perform regular maintenance

Regular maintenance increases the longevity of a spray booth, preventing unexpected and costly repairs. Intensive use of the booth may even require an appropriate maintenance schedule. The most qualified spray booth manufacturers can offer scheduled maintenance plans, tailored to the specifications of the customer’s facility and in accordance with their time availability, in order to better manage maintenance-related downtime. As the saying goes, prevention is better than cure.

Attention should be paid to the state of the filters, which should be properly checked and, if necessary, changed. Intake filters should be inspected periodically to determine their efficiency in removing impurities from the air.

The state of maintenance of the floor filters and exhaust filters is extremely important because their inefficiency can result in:

  1. an increased risk of cabin soiling
  2. reduced retention capacity of volatile organic compounds (VOCs) with release into the environment
  3. uncontrolled dispersion of VOCs increases the risk of paint deposition on the fan with possible unbalancing of the unit.

In any case, it is always recommended to use original spare parts approved by the manufacturer because they have the same characteristics as those installed in the original plant and therefore have been tested.

Monitor the control panel

The control panel can provide a lot of useful information about a booth’s health. For example, it can record how many hours of painting have passed since the last filter change, helping to optimize maintenance cycles. More advanced control panels can also monitor the status of filters, notifying the operator in the event of unexpected clogging.

Another way to maximize cabin efficiency is to regularly update the control panel software, ensuring top performance at all times and reducing the risk of malfunctions.

Keep the workspace clean

Keeping the workspace clean is also important: the area around the spray booth should be kept as neat as possible. Prioritize the areas where most of the dirt accumulates to reduce the amount of impurities that could enter the booth.

Space configuration is a key factor in this. When deciding where to set up the booth, you should always consider the workflow: for example, moving parts from the preparation area to the booth and then exiting on the other side is a cleaner process than returning the coated parts to the preparation area.

Take care of the lighting quality

The lighting of a booth can affect both the comfort of workers and the quality of the work itself. Clients often request well-lit workstations with specific shades of color that make it easier to detect any flaws resulting from an incorrect application of the product or, more simply, to check the correct gloss of the coated substrate. 

The market offers both LED lighting systems that allow to save up to 60% of operating costs and advanced neon tubes: these solutions are also highly efficient and eliminate the risk of shadows and reflections by proving uniform illumination without altering the colors.

To sum up, many factors can affect the efficiency of a spray booth. For individual advice on how to optimize your work processes or to find a tailor-made solution, contact our specialists