DeFelsko manufactures hand-held, non-destructive coating thickness gauges that are ideal for use by automotive paint detailers. They enable full service detailers to quantitatively measure and control the amount of clear coat removed when sanding and buffing automotive paints.

Ultrasonic models are available to either measure the total system thickness (like magnetic and eddy current gages) or the individual layer thicknesses in a multi-layer paint system. The affordable models are only intended for use over non-metal materials such as plastic.

What is clear coat?
The clear coat is polyethylene paint without color pigmentation. Thickness usually ranges between 1.5“ 2.0 mils (35 “ 50 microns). It is the final original equipment manufacturers coating applied to a vehicle to protect the (base) color coat from a hostile environment while providing both depth and a durable, glossy appearance. It is easily scratched and, once compromised, requires re-painting, as the base color has no shine or brilliance. Also, the clear coat provides UVR protection for the colored paint layer.

Car manufacturers now specify that the paint thickness be measured before and after any wet sanding or buffing. Measurements should be taken regularly since it is virtually impossible to see how much paint is being removed during the buffing process. Using a paint thickness gauge gives a professional detailer credibility and also acts as an insurance against ‘break-though’ of a clear coat, which would entail a re-paint.

What should the paint thickness be?
Unfortunately there is no absolute target value no thickness. There are many different manufacturers making many different models with a wide variety of paint formulations and specifications. Some vehicles may only have 3 mils (75 microns) of total paint thickness on the roof, while some SUVs may have 17 mils (430 microns) on their rocker panels. Some vehicles are repainted at the factory when flaws are detected during manufacture. Typically however a vehicle from the factory will have between 4 – 7 mils (100 – 180 microns).

Are these instruments known by other names?
Although most industries call them coating thickness gauges, the automobile industry also uses names such as paint depth gauge, paintmeter, refinishing gauge, dry film thickness gauge (DFT gauges), paint thickness gauge (PTG), mil gauge, banana gauge, spot checker, or paint gauge. Spelling is either American (gage) or British (gauge).

Where else in the auto industry are these instruments used?
Detailers require a simple gauge with good measuring accuracy and resolution to monitor the decreasing thickness of clear coat with buffing. But the same or similar instruments are used by body shops, dealerships, painters, appraisers, inspectors, and professional car buyers at auctions.

Cleaning is a preparatory step intended to remove dirt, dust, and other loose contaminants in order to allow full inspection of current paint conditions. Rejuvenation refers to the processes used to return a vehicle to its original showroom condition. The extent of rejuvenation is dependent on the customer’s expectations. Protection refers to the maintenance processes such as waxing that are used to keep the vehicle looking new for as long as possible after detailing.

Simple washing and waxing will not remove many types of surface paint damage; a rejuvenation step (polishing with an orbit or more effective high speed polisher) is added before the waxing step. When rejuvenation is required, detailers often polish the top clear coat layer of automotive paints to remove surface damage such as fine scratches, scuffs, swirl marks, oxidation, stains, paint overspray, tar, tree sap, acid rain or water spots. This polishing process is often referred to as finessing. Extensive paint problems may require the use of several sanding and buffing steps to bring the paint back closer to its original beauty.

Automotive manufacturers typically use one of two main types of paint systems in their vehicles. The most common used today is a clear coat system in which a thin layer of color is applied, followed by multiple layers of clear non-pigmented paint. Used less frequently today is a single-stage paint system that consists of the application of multiple layers of pigmented paint. Since most detailing chemicals are designed to work on both paint systems, the paint detailing process does not significantly change based upon the type of paint system.

Why measure?

To ensure consumer value and thus maintain profitability, there are two main considerations when justifying equipment and processes involved in the detailing process. Any added cost must result in improvements in either efficiency or effectiveness. While it could be argued that a detailer’s ability to take quick readings with a paint thickness gauge in order to determine the remaining paint thickness is an efficiency benefit, the primary benefit is the increase in effectiveness.

When the need to polish (sand and buff) has been identified it is important to evaluate the paint in surrounding areas. Most factory paint jobs seem to range from 4 – 7 mils (100 – 180 microns). Thinner readings indicate that the clear coat is almost entirely removed or in the case of single-stage systems that the primer is about to show through. As represented in the photo above, thicker readings are often an indication that repainting has occurred. When repainting is detected, the operator has a difficult task in evaluating the suitability (thickness) of the top layer of paint for buffing. No matter how careful the operator, buffing or polishing on thin coatings risk paint damage to the vehicle. When detailing thin coatings or unknown paint layer thickness, an alternative system such as hand polishing may be the only safe option.

After determining the paint system used on the vehicle and thus the expected paint thickness, it is important to determine the actual paint thickness. Even an experienced detailer finds it difficult to determine paint thickness, especially clear coat, through visual inspection. As thinner, more scratch resistant clear coats such as nano technology become more prevalent, it will become more critical to use high resolution electronic thickness gauge to determine how much paint thickness is being removed while finessing.

Because of the potential for removing the majority of the UV blockers, most auto manufacturers recommend that a maximum of 0.3 mils (8 microns) clear coat be removed as prevention from UV damage to underlying paint layers. In a worst-case scenario with a single stage paint process, buffing down to the primer may result in a costly trip to the paint booth.

Also consider that paint damage may not visually appear immediately. When too much topcoat is removed, premature failures such as fading or delamination may occur. Failures have the potential for lawsuits, unhappy customers and loss of reputation. Such risks can be alleviated by monitoring and minimizing the amount of topcoat removed, which is best done through quick and easy measurements with an electronic paint gauge.

Significant damage below the top painted surface may include deep scratches, etching, staining, and heavy oxidation. Just as simple washing and waxing will not remove some top layer paint damage, rejuvenation through sanding and buffing may not be adequate for removing deeper paint damage. It is therefore important to recognize the limitations before too much paint has been removed.