Detailing Paint Correction: Paint Swelling & Heat Explained

Learn How Heat from Paint Swelling Hide Defects during Paint Correction in Auto Detailing from OCDCarCare Los Angeles.

By Christopher Brown of 

Every auto detailing business offering paint correction (a.k.a. paint polishing or buffing) will, at one time or another, encounter the intense frustration caused by automotive paint swelling.

Imagine a detailer devoting a full day, or even two, into a vehicle’s paint correction to bring the a finish to an extremely high level. Naturally, 8-10 hours of continuous compounding and polishing exhausts a detailer. So at the end of the day they go home feeling accomplished, realizing the hardest labor of the project is completed– the paint correction. At this point the detailer starts envisioning the completed vehicle the next day, and the crisp large bills handed over as reward.

In the morning, the detailer inspects the vehicle, looking to start the day with positive boost and happy feeling from yesterday’s hard work.

Then. . . Out of nowhere, IT happens:


This chaos generally starts with involuntary and nonstop angry verbal outbursts. These fits feature four letter words and phrases that would make an army drill sergeant blush. Sometimes they last for minutes, sometimes they last for hours.

Frequently, small or medium sized objects unexpectedly fly across the room at high speed.

Other times, intense anger and confusion create a void–filled with utter silence.

You might wonder,What on earth could cause a detailer to break into drastic and immediate fits of disgust, frustration, and possible rage?


When first encountered, automotive paint swelling might seem a mystery, paralyzing most detailers with feelings of sheer horror and shock.

They discover some or most of the vehicle’s paint no longer appears as a dark reflective mirror as it did after paint polishing the day before. Instead, the paint’s surface may seem unfinished, looking grey and hazy. Or, vehicle panels still show many of the original light, medium, or deep scratches and/or other paint defects which the paint correction seemed to remove the day before.

But how, in the name of all that is good and holy, is this possible??” the detailer asks. Repeating the phrase over and over in their mind, and/or aloud, as they inspect the vehicle in a trance of horror, frustration, rage, and disgust.

This must be a bad dream, they tell themseleves–over and over.

However, the unfortunate truth of the vehicle’s surfaces reveals a real world condition. The cause… automotove paint swelling.


Paint Swelling via Paint Correction (a.k.a. Polishing or Buffing) Defined

Automotive Paint Swelling is a temporary condition where paint expands in size, or “swells” due to overexposure to heat (and chemicals) and hides defects.

As a result of this increased mass from the energy of heat, and other contributing factors, the paint has “puffed up” and locked defects within the swelling and hidden them from sight. Therefore, detailers are unable to see, unable to access, and unable to correct (‘buff out’ or remove) these defects while the swelling persists.

Often times, this condition occurs quickly and detailers are completely unaware that many defects go uncorrected. This is because paint swelling may occur either at a gradual or very quickly, depending on the characteristics of the paint system.

As a general rule; the levels of heat and swelling of a panel rise proportionately to the amount of friction created during sustained periods of polishing. This explains why paint swelling is not immediately noticed. Most detailers have no idea a problem occurred until after vehicle services are fully completed, in most situations.

The cause of Automotive Paint Swelling is a transfer of heat (energy via friction) into the paint’s molecules.

When automotive paint swells up, it hides many sorts of defects. The defects most commonly hidden are light and medium scratches, commonly referred to as “spider web swirl marks.” Sometimes even heavy scratches may be temporarily hidden inside the swollen paint structure.

Additionally, paint swell may also hide the light defects associated with final polishing steps. These defects include micro marring and tick marks. These are the fine controlled defects, resulting from a previous heavier polishing process, called ‘compounding’ which removed the original paint defects.

Paint swell also has the ability to hide other paint defects during paint polishing like hard water spots. This sub-topic, nicknamed “Phantom Water Spots” was tackled in a previous OCDCarCare Los Angels Article: Water Spots Appearing After Ceramic Coating Application: Explanation & Removal Method

Why Paint Swelling is a Nightmare Type Problem for Auto Detailers

Imagine yourself as a 20yr professional brick mason. On your day off you decide to finally lay the new backyard brick porch area that you’ve put off for years. You commit an entire day to: preparing the land grading, hand selecting the best bricks, and then laying the bricks in a pattern that pleases you and your spouse.

The next morning you walk outside. Your initial half smile of accomplishment quickly fades to disgust and disbelief. You look at the patio and discover all of the careful work from the previous seems looks ruined.

The bricks you placed and triple check with a level from (3) reference points are now mostly out of alignment. They look like the work of 5th grade science project, constructed last minute! Definitely NOT the work of a seasoned professional.

Paint swell gives auto detailers a similar sort of slap in the face feeling. Eventually, anyone who polishes or paint corrects enough vehicles will experience the extreme pain and frustration caused by paint swelling. It instantly makes all previous labor on the project seem worthless because much of the paint polishing work requires a mulligan.

What seemed like a nicely finished surface the previous evening, is later discovered as a very rough and unrefined surface. It desperately needs hours upon hours of more work.

Generally, automotive paint swelling shows itself in one of two ways:

  1. The swelling dies down quickly and the defects appear. They become visible within 3-6 hours on the same day of the initial paint correction.
  2. After a day, or two, or sometimes three, the swelling finally fades and the defects reveal themselves. In this time project is completed, paid for, and the vehicle is back home in the client’s garage.


How Frequently does Paint Swelling Occur in Auto Detailing?

Paint swell is a more common occurrence than most auto detailers believe or will freely admit to. With current technology it is very easy to cause paint to swell to a level to hide defects on thermal sensitive paint systems.

You may be wondering: “If that is the case, then why is paint swelling not a common topic of discussion among detailers?”

Paint Swell is mostly an unspoken topic within the auto detailing industry for a few probable reasons:

  • Ego. Professional Detailers don’t want to admit to peers (and often themselves) they encounter issues in their work.
  • Light to Medium colored vehicles don’t prominently display defects as easily as dark colors.
  • Metallic Paint. Metallic automotive paint systems have variation in appearance and hide defects much more effectively than their non-metallic cousins.
  • Very little information regarding paint swell, and its associated variables are available. Therefore, the detailing industry avoids the topic.

Do All Automotive Paint Systems Swell?

Paint swelling occurs on all paint systems because automotive paint is engineered as a thermal elastic structure. It is designed to maintain its structure while frequently dealing with constant expansion and contraction for a non-stop barrage of heat sources.

Therefore, on some level, all paint systems swell when introduced to heat. However, not all paint systems exhibit negative consequences of paint swelling equally. Some paint is more sensitive and tends to swell much easier, and with a greater degree, than others. These can be defined as ‘thermally sensitive’.

The negative effects of paint swell are most visible when dealing with non-metallic dark colors such as jet black. It takes a great deal of effort to fully remove all defects which are always visible on jet black surfaces. This is because darker non-metallic base color layers act as a solid mirror, mercilessly highlighting every paint defect and imperfection. This is why dark paints look so impressive when finished to a high level, they most accurately depict the surface in great definition of color, depth, and reflection to the human eye.

Think of dark non-metallic paint like a black velvet couch, in a home occupied by a pair of big white dogs– Siberian Huskies. Every piece of white hair or dust that lands on, or sometimes even near the couch, sticks out like a sore thumb. And it is the same with defects on the canvas of a dark painted vehicle—they stick out like no other.

Dark non-metallic vehicle paints often require considerable effort and time to finish down, or fully refine. It’s intense work to get them to look their full, deep, rich pure colors without any trace of haziness.

This is precisely why paint swell is demoralizing for paint polishers. The detailer believes they have triumphed over the paint defect demons, finishing the paint to a high level. However, joy sometimes fades quickly when viewing the vehicle the next day. Shocked disbelieving eyes show a battleground (the paint) still containing a considerable army of resourceful and sometimes formidable defect demons.

How Paint Swelling Occurs in Auto Detailing

Paint swelling is the reaction of the vehicle’s paint system to heat. It’s similar to swelling in the human body. Think about rolling or breaking an ankle.

When injured, the human body immediately initiates protection protocols. To protect the load bearing hinge joint of the ankle, the body immediately uses swelling to protect the trauma zone. This is the body’s method of immobilizing the area by preventing any movement of the injured joint.

Shortly after injury, the ankle is unrecognizable. What normally appears as a sharp pointy bone, on the outside of your foot, quickly looks like a bloated mass of flesh with a large 90 degree bend.

When automotive paint swells, it has the ability to hide defects just like the swelling of the injured ankle joint.

The severity of ankle swelling is generally proportional to the level of injury. A minor tweak might have almost no swelling. However severe rolling of the ankle, or a break may cause mild to massive amounts of swelling. This level of trauma can make the ankle puff up to half the size of a grapefruit, and sometimes more.

The concept is similar with automotive paint swell.

The amount of paint swelling is generally proportionate to the amount of energy (heat) caused by paint correction abrasion, transferred to the paint. The heat causes the paint molecules to speed up and spread further apart. The need for molecules to maintain their optimal distance causes ‘the swelling’ or expansion of the paint system.

The more heat generated from polishing, and absorbed into the paint, the greater the level of paint swelling that may occur.  Ultimately, the thermal sensitivity of the paint system’s formulation dictates the reaction to heat. Thermal sensitivity influences both: the speed at which swelling occurs and the capacity for expansion (how much) swelling may occur.

When paint is swollen, similar to a freshly sprained ankle, no problems can be fixed. Additionally, the area cannot be accurately seen for what it is and diagnosed–until the swelling has passed. The swelling may completely mask or hide defects within itself. Therefore, while the swelling remains defects cannot be accessed for removal.

Swelling may also be the reason why the corrected panels looked finished or “good to go” some 8-12 hours earlier. Yet, when inspected the next day, after the paint cooled and returned to its normal size, all defects previously suspended inside the swelling are highly visible.

13 Common Paint Correction/Polishing Variables Contributing to Automotive Paint Swelling

This list outlines the primary factors which have the ability to contribute to potential paint swelling.

Most of these variables add heat directly into the paint’s structure via the friction of paint correction. However, more than a few common detailing procedures utilize chemicals designed to ‘open up’ the paint to allow deeper access into its porous structure.

The process of using chemicals to open up paint is called “chemical cut.” Generally, these refer to heavy compound solvents. When detailers use these correction liquids, a direct consequence is that heat is able penetrate faster and deeper into the matrix of a paint system. This causes the paint to swell from the start. It has the potential to cause severe levels of swelling when paired with high levels of sustained mechanical abrasion caused by paint polishing. This is a byproduct of using heavy compounds containing high levels of solvents.

The list below is not complete. There are definitely more factors that could add to paint swell. However, the following list will most likely help auto detailers pinpoint the vast majority of common variables directly contributing to paint swelling.

Typical Automotive Paint Swelling Variables Related to Detailing Paint Correction:

The Initial Formulation of the Automotive Paint System

Arguably the chemical make up of a vehicle’s factory paint system is the most important toward its tendency of automotive paint swelling. This is because the original formulation of a paint system dictates its thermal sensitivity or ability to absorb and dissipate heat.

A main contributing factor of a paint’s ability to dissapate heat (and avoid swelling) has shown to lie within the density (concentration) of a paint’s solids content. Generally, the denser the amount of the solids contained within the paint formulation, less heat and swelling issues seen.

A large majority of paint swelling issues tend to occur on paint systems containing low levels of solids. High solids paint systems are thicker and therefore have a greater mass. More mass allows automotive paint systems to better distribute and dissapate heat more effectively.

A Panel’s Substrate Composition

A substrate is the type of material a vehicle panel is constructed of. Substrates are covered in layers of automotive paint according to their composition. Some typical paint coat layers include: Precoat, Primer, Base Coat (color coat), and Clear cost.

The panels of most vehicles were primarily made of steel or aluminum in previous eras. In modern automobile manufacturing, all vehicles contain many combinations of substrates. Most modern vehicles (especially commuter vehicles) are a mix of aluminum and various plastics. More exotic vehicles may also contain different types of carbon fiber, Uber light metals, and advanced composite plastics.

The relevance of a substrate in regards to paint swell, is its ability to dissipate heat. Some substrates, like plastic, heat up quickly and hold heat for long periods of time. And other substrates, such as aluminum, react slower to heat. They require more energy to both heat up and to keep hot over time.

A substrate’s composition directly impacts a paint system’s heat tolerance. The longer a substrate holds onto heat, the greater the percentage of the overall heat will transfer into the paint system. And the more heat absorbed into a paint system, the higher the likelihood for that paint system to swell.

Starting Surface Temperature of a Panel or Section

During detailng paint correction a panel needs to start off at the coolest temperature possible. A warm or hot panel has less of a temperature cushion to sustained heat from polishing friction. When polishing it is best to keep surface temperature as low as possible. Warm or hot panels guarantee paint systems will heat up quicker. This directly translates to a greater tendency to swell during any paint polishing processes.

The absolute danger zone for induced friction from paint correction (polishing) is 130°F. However, its highly advised to never habitually polish so surface temp reach anywhere near that level. So its best to stay under 110°F or lower.

Ambient Temperature of Environment

If a vehicle panel is out of the sun, but resides in shop with an ambient temperatures between 90°F (~32°C) to 110°F (~43°C), its resting temperature (control) is still greatly elevated, compared to a vehicle resting in 75°F (~24°C).

This elevated temperature already puts the paint system at a disadvantage for swelling– before polishing begins.

Decon Process: Chemicals Used to Decontaminate the Surface after Initial Wash

Some chemicals used to decontaminate surfaces (strip) them of built up dirt and contamination (a.k.a. traffic film) are aggressive enough to swell paint.

Machine Choice for Paint Correction

Machine choice for paint correction directly impacts the level of heat generated by a pad face from the friction of polishing. This directly influences the level of direct heat introduced into the paint system.

Rotary Polishers: Rotary machines run the coolest due to their limited motion (spin only) and due to their direct drive mechanism. Pads attached to direct drive motions cannot stay in a single spot for sustained periods of time. To do so will quickly build up extreme heat in a single spot and will greatly elevate the chance to burn paint.

D.A. Polishers: Dual Action machines add the most heat to surfaces. This is because the machine combines the two movements of spinning and oscillation (lateral back and forth). Combining these movements make the active machine action more violent. This increased violence means more friction which ultimately adds higher levels of heat into the paint polishing process.

Pad Type Choice for Machine Polishing

Pad choice has major impact on the amount of heat driven into a painted panel via machine polishing.

Wool Polishing or Buffing Pads run the coolest on a rotary due to their concentration and the ability of air to flow between fibers.

Foam Polishing or Buffing Pads are all over the map in terms of heat production. They carry a wide range of aggressiveness due to their many and varied attributes of different: thicknesses, foam densities, cell types, etc.

The takeaway: foam pads generally offer a middle ground for heat generation. “Cutting” foams will generate more heat than “finishing foams.” And all will produce more heat than wool on a rotary.

Microfiber Polishing or Buffing Pads run the hottest of all pads. It’s not even a close race. This is due to a few factors. First, as a material, microfiber has a much higher inherent aggressiveness than foam or wool. Secondly, microfiber pads, at a minimum, probably have 100x the surface area of a foam pad to perform work. This highly increased surface area creates a huge amount of heat when compared to foam or wool pads.

Number of Processes Completed During Paint Polishing

The more polishing processes required on a vehicle, the more heat that will result, driving itself into a panel. Simply stated, to bring a beat up surface to a quality level that is near or at defect free, the higher the friction required. This increased friction has the ability to transmit more heat into to the panel and paint system to induce swelling.

E.g. A One-Step Paint Correction consists of a single process. This includes a finish polish or a medium compound typically paired with a foam pad to complete the task. Since multiple paint correction steps are not necessary, lower levels of heat occur and transfer into the paint system.

In contrast, a Two-Step Paint Correction consists of two processes. The first stage (compounding) typically pairs some of the most aggressive compound and pad combinations to quickly and efficiently remove the majority of defects. The compounding step alone is much more aggressive than a one-step paint correction due to the pad and liquid choice. When followed up with with the second stage (the finish polish step) the overall aggressiveness of a two-step paint correction is significantly greater.

Correction Liquid Choice (Amount of Chemical Cut)

Some paint correction liquids, generally heavy compounds, recruit the aid of chemical mechanisms to help with defect removal. These solvents within correction aid to an effect known as “chemical cut.”

These compounds rely on heavy solvents to chemically open up or swell the porous paint structure. This swelling allows the liquid’s emulsion, containing the abrasive particles, the ability to penetrate deeper into the paint’s structure. This enables the compound to access and remove more defects at a higher rate of speed.

Amount of Downward Pressure Used During Polishing

The amount of pressure applied to a polishing pad (via the polishing machine and it backing plate) has a drastic effect on how aggressive machine polishing can be. The more pressure placed on the pad the greater the overall level of friction generated by the process.

Heavy pad pressure instantly raises friction levels. Heightened frictions levels increases heat which is transmitted directly into the paint system. The more heat transmitted into a paint system, the higher the likelihood for paint to swell.

Arm Speed Used During Polishing

Arm speed also plays a direct and important role on the overall aggressiveness level of machine polishing. The slower the movement of arms over an area the longer the machine, pad, and correction liquid have to work over a given area.

Therefore, the slower the arm speed the more friction created during each pass of the machine. More friction leads to increased heat transferred to the paint system with each pass.

Number of Passes Completed During Each Paint Correction (Polishing) Process

The number of passes completed for each process, for each panel, contributes to the overall amount of friction and heat transferred into a panel.

The lower the number of passes completed per process, the less heat generated and therefore transferred to the paint. Inversely, the higher the number of passes per process, the greater the level of heat generated and transferred to the paint.

Type of Final Panel Preparation Product & Method of Use

The type of panel preparation product used on a panel to remove carrier oils after compounding or final polishing steps can further contribute to automotive paint swelling.

A panel prep with mild solvents may not swell paint much. However, panel preps with high concentrations of alcohol, or heavy solvents, may greatly increase the swelling effect on a vehicle’s paint system.

Additionally, some detailer procedures involve using panel wipes on multiple occasions during their polishing processes. Some use it at the start to strip surface contamination. Other detailers use it multiple times during paint correction: once after heavy compounding and then again after finish polishing.

Every instance a solvent based panel prep touches painted panels, or sensitive substrates, the more it promotes swelling of the paint system or surface.

Takeaways of Understanding Automotive Paint Swelling & Paint Correction 

Hopefully, at the very least, this article has demonstrated that many common paint correction (polishing) factors directly contribute toward the potential for a paint system to swell up and hide defects.

At minimum, the 13 variables listed above are the ‘usual suspects’ which have probably contributed to automotive paint swelling you may have experienced. 

Some of these factors definitely have more of an impact on paint swelling than others. However, when a few or more factors stack, they gradually build upon one another and greatly increase the potential for a paint system to swell.

NOTE: It is plausible to say that all paint systems swell to a certain degree. This is because automotive paint is designed as a thermal elastic structure. Therefore, it must have the ability to accept and dissipate heat from many sources including: direct ambient heat sources (sun & air) and mechanical heat sources (e.g. engine and braking systems).

All automotive paint systems are engineered to expand and contract to constantly deal with heat—however, not all handle heat equally.

Some paint systems are more sensitive to heat and require lower levels of heat to react in negative ways for auto detailing.

These thermally sensitive paint systems have the tendency to swell:
A) faster, sometimes requiring less energy.
B) to a greater degree–than paints formulations with less heat sensitivity.

The swelling tendency of paint is further compounded when thermally sensitive paint systems are paired with substrates demonstrating poor heat dissipation characteristics. These substrates hold the heat, passing it directly into the paint system, creating even more of a swelling issue.

This article is not designed as a solution for heat problems encountered on all paint systems. However, it can serve as an invaluable check list for detailers, guiding them to understand the variables may have may have contributed to a paint swelling which covered up or hid defects during paint correction.

Hopefully, this article proves useful to assist detailers to understand automotive paint swelling and the contributing factors. The great news: with enough education and dedication, detailers can adjust their procedures enough to greatly minimize or prevent the occurrence of automotive paint swell during all stages of paint correction (paint polishing).

“ALWAYS Keep Learning to Strengthen Your Passion & Your Business.”

© Christopher Brown – OCDCarCare Los Angeles

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Christopher Brown