It's really not surprising....
At one time or another most of us will experience this disaster while detailing. I’m sure many of you have heard the term “burn through” and it’s generally associated with breaching the clear coat. The term burn through is a throwback from the days when the rotary polisher was king and the dual action polisher wasn’t even thought of.
Burning through the paint in those days was primarily due to friction. A rotating wool bonnet under pressure and in contact with the paint results in friction and we all know what happens when we rub our hands together quickly; things begin to get hot. As the temperature increases the paint softens and before you know it; “
Burn Through”! :doh:
Dual action polishers by design operate in an orbital manor and do not rotate. Now before anyone posts an objection let me elaborate.
Under certain applied pressures or free wheeling, a dual action polishers pad will rotate but with minimal force. The main motion of these machines is oscillation, generally at high speeds and in small circles but generate almost no heat.
Automotive Paint
Over the years automotive manufactures have been on a quest to lower manufacturing cost and just one of those areas is paint. By doing so, these improvements translate directly to their bottom line as profits.
The actual film thickness of paint is what I call SCARY THIN, meaning it doesn’t take much effort to accidentally sand or compound through a layer. A layer of paint is so thin today it’s measured in microns rather than thousands of an inch.
Corrosion
How many of you can remember the days when a panel on a brand new car would show sighs of rust or corrosion in the first 2 years? You don’t have to go that far back because this was pretty much the norm in the 70’s and 80’s.
To combat this, car manufactures teamed up with paint suppliers like
DuPont to develop coatings and processes to greatly reduce or eliminate corrosion and rust through.
Microns
Microns are typically associated with either of the two following symbols; µ or µm
Just how big or small is a micron? 0.001mm, or about 0.000039in
To illustrate this lets put this in perspective by comparing a known and relate it to microns. On average, a human hair is about 100 microns or 100µm.
1µ = 0.00003937in
10µ = 0.0003937in
100µ = 0.003937in
Now that we know how think a human hair is, see how it compares to the paint film thickness on most cars today....It's thicker than any individual coating applied and might be equal to all of the coating thicknesses combined!
Paint Application
Automotive paint is applied in layers and each one is designed to to work with out bond to the previous later. Today protective coating and paint layers can total 5 or more and at varying thicknesses. The photo below illustrates not only the coating but the average film thickness....
- Phosphate - 1µ or 0.00003937in
- Electrocoat or E-Coat - 25µ or 0.0009843in
- Primer - 25µ or 0.0009843in
- Base or Color Coat - 20µ or 0.0007874in
- Clear Coat - 50µ = 0.001969in
Phosphate
Phosphate coatings offer excellent corrosion resistance. These coatings are usually applied to carbon steel, low-alloy steel, and cast iron. Phosphate coatings are most often applied by either spraying or immersing the substrate into a solution of dilute phosphoric acid combined with other chemicals that assist in the coating process.
Electrocoat or E-Coat
An unfinished panel is immersed in a bath containing the electrophoretic paint emulsion, and then an electric current is passed through both the product and the emulsion. The paint particles that are in contact with the product adhere to the surface, building up an electrically insulating layer thus improving the corrosion resistance of the metal..
If you look hard enough on You-Tube I'm sure you'll find a factory video showing the frame and body of a car being submerged in a bath to effectively these coating in every nook and cranny.
Primer, base coat and clear coat are pretty self explanatory so I won't go into detail.
Steel Thickness
The thickness of the sheet steel that makes up the majority of cars today has over the years become thinner and thinner. Some of this initiative is related to the overall weight but also fall right in line with lowering costs of raw materials.
What body and paint shops typically see in a single stage paint job.
In this photo you'll see the typical finish layers applied at the factory. Many times though shops uncover damage and additional paint repair that can add several subsequent layers that must be dealt with properly.
This is a great example to illustrate different types of surface defects and their relative size when compared to one another.
Paint is only so thick. If you're using a heavy cut pad and an aggressive compound on a dual action polisher and hold it in one spot just a little too long what do you think will happen?
Sand Through
Be careful out there.....
rops:
