Filling/Masking

We may have heard the horror stories or perhaps we have experienced this ourselves. We have done everything in our power to polish our paint to a swirl free, high-gloss finish, and we have done everything to ensure those results are true. Perhaps we have wiped the surface with a solvent or rubbing alcohol to inspect the finish. Yet, slowly, over time, circular paint defects return. What causes this? Is it impossible to get a perfect finish? What can we do to prevent it?


What Is Filling

Filling or defect masking is when the paint has an artificial appearance. Swirl marks, haze, and holograms (and other normally visible paint defects) that are still present are temporarily invisible. Drop back is a term used to describe when the paint defects re-appear.

Some products are designed to glaze over paint defects and reduce the defects` appearance. These products can be a pure glaze, a specially designed wax/sealant or the combination of an abrasive polish and paint filling agents. The latter is commonly used in body shops and production detailing environments where quick turn around time is required to maintain profitability. The fact is, that truly correcting paint defects, even with modern technology, is time consuming.

Some ingredients that are used to create a filling effect are:
  • some amino functional (cross linking) silicon polymers
  • carnauba, bee`s, montan, or other natural occurring wax
  • kaolin clay



Unintentional Masking

While some products are designed to mask paint defects and purposely use ingredients to create an artificially level paint appearance, many polishes do not. There are a wide variety of polishes available that are designed to remove paint defects completely while creating a high-gloss finish without the need to mask the defects. However as a result of their application process, ingredients, or reactions with existing products on the paint you can still have some unwanted filling or masking of paint defects.

The ingredients in many polishes, particularly the oils that provide lubrication, can serve to temporarily hide paint defects and make an accurate assessment of the paint condition difficult. These oils are designed to resist abrasion. They must stick to the paint and provide the necessary lubrication needed for paint polishing. If they can remain steadfast against a wool or foam polishing pad that is moving with pressure at 40 mph, a buffing cloth may not remove them completely. Chemically `stripping` or using a paint cleaner to remove these oils can be necessary to avoid drop back.

Some products that are commonly used to remove any oils, waxes, or products that can be used for product filling:
  • diluted isopropyl alcohol (15-50% alcohol/water solution)
  • mineral spirits
  • body-shop pre-paint solvents
  • window cleaners (that use isopropyl alcohol
  • detergent (grease-removing) soaps (particularly body-shop safe polishes)
  • manufactured paint cleaners (CarPro Eraser for example)


Generally, when using a chemical stripping agent the process is the same. Spray a liberal amount of stripping agent onto the paint and agitate with a microfiber cloth. Then immediately wipe the cleaning agent from the surface before it starts to to evaporate (either with the dry/clean side of the microfiber or a second microfiber) to avoid redepositing.

Does Dish Washing Detergent Effectively Strip Paint?”

Yes and no, and not really.... The first factor that will determine how effective dish washing soaps are is how resilient the product they are being used to remove is. Some polishes and glazes, particularly those that are not body shop safe, will have silicones and waxes in them that may be detergent resistant.

Another point to consider is that most dish washing soaps are not designed to rinse completely clean. This may sound strange at first, but many of these soaps are designed to create a thin film on the surface to help sheet water away (avoiding water spots on dishes). The longer the soap is allowed to sit on the surface, the thicker the film deposited, the water beading is (temporarily) diminished. This lack of water beading can lead many to believe to surface has been effectively stripped when the result is actually a factor of additional product being added to the surface. Anything that leaves something behind on the surface is going to achieve the opposite effect. Even all-purpose cleaners can leave some residue on the paint.

Dish washing soaps and all-purpose cleaners can help accelerate the cleaning of stubborn products but they should not be solely relied on to clean the paint. Follow their use with a chemical cleaner if you truly desire a true finish.


Paint Swelling, The Unintentional Filler

Automotive paint is classified as a semi-permeable membrane, like your skin. Some chemicals can penetrate paint easily while other chemicals will stay on the top of the paint. Paint is also elastic, like your skin. This means that paint, like your skin, is constantly changing shape and absorbing (and out gassing) chemicals. As my friend, Jason Rose, from Meguiar`s told me, “100% pure petroleum jelly (Vaseline) will actually make your skin thicker by putting oils into tissue pores. It will also make your skin stretch further by making tissue have more tensile strength and elongation (actual technical terms paint experts use to specify elasticity.)"

As we polish paint we can experience paint swelling due to different causes: 1) Heat 2) Chemical Absorption

Heat- The act of polishing (removing material) requires friction. Heat is a by-product of friction. Paint, like most matter in the known universe will expand when heated and contract when cooled. The warmer it is, the more flexibility it has (thus you may have seen a dent removal guy warm a body panel to reshape a dent and prevent the paint from cracking). The very act of creating the friction necessary to polish paint will warm the body panel and the paint.

Chemical Absorption- As noted above, paint, like skin, absorbs chemicals. As in the Vaseline example from Jason Rose above, chemicals that absorb into the paint can increase its thickness, causing it to expand multi-dimensionally (like a balloon that is being filled with air).

Combination- The combination of chemical and temperature related swelling is the most likely effect. As some chemicals, which are being forced into the paint during the polishing process heat, they will compound the expansion (particularly true of solvents and oils).

Heading back to Jason Rose to finish this thought, “Now, you must know that paint elongation (thus swelling) is a VARIABLE. This means what you experienced on one car does not mean all cars. What you experienced on one BMW does not mean all BMWs react the same. And especially when you buff on fresh paint with any product you can experience varying degrees of paint hardness and thickness on day one vs day four, or 6 months later.

Take a freshly paint car and sand/buff it/ two steps of sanding and two steps of polishing. We should have removed a lot of paint, right? Paint thickness should be shorter, right? Not always. I have COUNTLESS times measured taller thicknesses on fresh paint after removing a lot paint. Why? How? Fresh paint is still full of escaping solvents. Buffing heats up paint. Solvents, resins, and other ingredients in paint swell when you heat them up (You know the whole liquid/gas thing that helps bombs work. I,m not a chemist, but I know something is working there.) By measuring this same paint daily for 3 months, you will see that paint thickness has a life of its own ”

Unfortunately, for detailers or enthusiasts, paint swelling is extremely small and impossible to visually inspect for. (expansion of 1/10th of a mil or 1/10,000th of an inch would be excessive). Even this small amount of swelling, caused by chemical reaction, heat, or a combination of both, could be enough to mask paint defects.

Chemically stripping the paint will not remove any chemicals that have absorbed; attempting to cool the paint may not make the original shape return. Instead it may take hours, weeks, or months. Defect masking via swelling is not a common occurrence, but it can explain unexplained paint defect drop back.


Taking The Steps To Avoid Draw Back

The first question to ask yourself is whether or not you should consider worrying about draw back in the first place. If you are detailing a car professionally and guaranteeing long-lasting results then it would be necessary. If you are maintaining your own vehicle, which you keep a fresh coat of wax or paint sealant on, and lovingly polish every 6 months to a year, then it may be overkill.

  1. Start by wiping the paint down thoroughly before polishing with a dedicated chemical stripping agent. This will remove any waxes, silicones, or polymers that may cause unwanted reactions when exposed to the machine polishing process.
  2. Use the least aggressive method, including machine choice, required to polish the paint. The lower the level of friction used, the less likely paint swelling (as a result of heat) will occur.
  3. Use polishes that are are labels as "body shop safe". These polishes are designed with out the use of waxes, silicones, or any ingredient that could contaminate the polishing process.
  4. Complete your polishing by using a dual action polisher instead of a rotary style polisher. This way, if there is any unwanted drop back, it will be in the random pattern that a dual action polisher creates instead of the direct drive linear motion of a rotary polisher. Modern advancements in pads, chemicals, and even techniques allow dual action polishers to create the same levels of gloss as other polisher styles while reducing the heat created as well.
  5. After polishing use a chemical stripper to remove any polishing oils and residues.




Maintain Your Finish Properly

Keeping a fine of wax or paint sealant on the paint will dramatically reduce the chance of drop back.

Any wax or sealant that is working is to some degree of filling/masking. This is a result of the nature of how the product works and attaches to the paint surface, as well as well as how it creates gloss. Waxes and sealants are designed to deposit themselves on to the paint surface. Any areas that have micro-fine scratches and swirl marks will, as a result, receive some degree of filling.

Some waxes will fill to a much higher degree and some are designed as a paint filler from the get-go.

Washing your car carefully, using proper technique and high-quality soaps, will help keep your wax or sealant intact, further reducing the chance of drop back from occurring.