Aircraft paint is not automotive paint, and the difference is not pride

A car has a thick, forgiving finish over a rigid body that never leaves the ground. An airframe has a polyurethane topcoat of roughly 50 to 75 microns over a structure that flexes in flight and swings through a huge temperature range on every leg. Almost everything that follows in how the two are cared for comes out of that one difference.

This is not a point about pride, and it is not an argument that aircraft work is harder. It is a materials point, and it has consequences that show up in the first ten minutes of any job.

The number that matters is the film thickness

Aircraft topcoats are engineered thin because every pound of coating is a pound of payload that never comes back. Sherwin-Williams publishes a dry film thickness of 2 to 3 mils, which is 50 to 75 microns, for Jet Glo Express. PPG publishes 50 to 75 microns for Desothane HS. AkzoNobel publishes 25 to 75 microns for Aerodur 3001 basecoat. Those are the same numbers from three different manufacturers, and they are not a coincidence: all three products are qualified to SAE AMS 3095, and the Sherwin-Williams product is also qualified to MIL-PRF-85285E.

For scale, an average human hair is around 70 microns across. The entire decorative and protective layer on an aircraft is about one hair thick. Everything a polish touches lives in that band.

An automotive finish is a different animal. It has a clearcoat over a basecoat and a comparatively generous total build, and it is sitting on a panel that is not expected to flex, pressurize or cold-soak. That is why a body shop can wet sand and buff a car repeatedly over its life and an aircraft cannot take the same treatment. There is not as much there.

The finish is a system, not a coat of paint

Under the topcoat is an epoxy primer. Under that is a conversion coating or an anodized layer. Under that is clad aluminum or composite. Each layer does a different job, and the corrosion protection is mostly happening below the part anyone can see.

That is the real reason a burn-through matters more on an aircraft than on a car. On a car you have damaged the appearance. On an aircraft you may have opened a path to the substrate, and the FAA’s own corrosion guidance, AC 43-4B, is largely a document about keeping that path closed. We wrote about that in more detail in cleaning frequency and corrosion control.

The airframe moves and the car does not

Skin temperature on an aircraft runs from well over 100 degrees sitting on a ramp in Florida in August to well below freezing at altitude, sometimes inside the same hour. The structure expands and contracts through that range on every flight, and the coating goes with it. Aircraft topcoats are formulated for that flexibility, which is part of why they behave differently under a machine polisher than an automotive clearcoat does. They are not simply softer or harder. They are built for a different set of loads.

What is within reach on an airframe has no automotive equivalent

On a car, almost everything within reach of a wash mitt is either painted steel, glass, plastic trim or rubber. On an aircraft, within a few inches of each other you can have clad aluminum, magnesium components, acrylic or polycarbonate transparencies, elastomeric de-ice boots, composite panels, exposed sealant, unpainted polished metal and static wicks.

Every one of those has a different chemical tolerance, and the one that matters is always the least tolerant thing your product can reach. Alcohol crazes acrylic under stress. Alkalinity attacks polycarbonate. Solvents that would be unremarkable on automotive trim will attack certain de-ice boot materials, which is why the Goodrich manual for the black standard pneumatic de-icer specifically warns against using MEK on Estane boots. The FAA’s own airframe guidance, AC 43.13-1B, tells maintainers not to use gasoline, alcohol, benzene, acetone, lacquer thinners or window cleaning sprays on transparent plastics because they soften the plastic and cause crazing. Window cleaning sprays. The thing in every hangar.

Which is why the process is different, not just the product

Every cleaning process is governed by four variables that trade against one another: time, agitation, chemical and temperature. Lower one and you have to raise another to get the same result.

On an aircraft, three of the four are capped. Agitation is capped by the finish. Chemical is capped by the least tolerant material within reach. Temperature is capped by the substrate. The one that is not capped is time, and time costs labour and damages nothing. That is the whole of our method, and it is why a company that does cars and also takes airplanes will tend to run into trouble: the habits that make automotive work efficient are the three variables an airframe will not give you.

A crew that is behind schedule reaches for pressure, for a hotter or stronger product, or for a more aggressive pad. Every one of those is borrowing against the finish, and the bill does not arrive on the day. It arrives at the next repaint, when the shop finds there is not enough film left to correct and the aircraft goes into strip and paint earlier than it should have.

What this means if you own one

Two practical things.

• Ask what the crew is trained on specifically. Not whether they are experienced, but whether their training covers the materials on your aircraft. Ours is recorded per team member per service and we can produce it, which is the point of putting it in the platform rather than in someone’s memory.
• Be suspicious of anything that promises an automotive-style transformation on a schedule that assumes automotive-style aggression. Correction on an aircraft is a considered decision about spending film thickness, not a routine step. We cover the arithmetic of it in paint correction and protection.

None of this makes aircraft work mysterious. It makes it bounded. The people who do it well are the ones who understand where the boundaries are before they start.