New paint, and how long before anyone should touch it

Dry to fly and ready to be washed are two different milestones, and they are weeks apart. The first is measured in hours by the coating manufacturer. The second is measured in about thirty days by the people who repair the consequences of getting it wrong.

Fresh paint is the most fragile a finish will ever be, and it usually arrives on the ramp at exactly the moment nobody has time to think about it.

The manufacturer’s number is about airworthiness, not durability

Aircraft polyurethane topcoats cure by chemical cross-linking, and the manufacturers publish what they call dry to fly: the point at which the film is developed enough for the aircraft to return to service.

PPG publishes dry to fly figures for Desothane HS CA8000 that depend on the activator and the temperature. At 20 degrees they run from 90 hours down to 8 hours across the activator range. At 25 degrees, 72 hours down to 6. At 35 degrees, 36 hours down to 6. There is also a force cure option: 30 minutes flash off at around 24 degrees followed by 60 minutes at 49 degrees.

Sherwin-Williams publishes air dry figures for Jet Glo Express at 25 degrees and 50 percent relative humidity: tack free in 3 to 4 hours, to tape in 6 to 8 hours, maximum recoat 24 hours. AkzoNobel publishes dry to tape for Aerodur 3001 basecoat from 1 to 2 hours to 6 to 7 hours depending on the activator.

Read those carefully and you notice what they do not say. None of them tells you when it is safe to put a cleaner and a wash mitt on the surface. That is a different property from the one being measured.

The number that answers the actual question

Comes from the MRO side rather than from the coating manufacturers.

Duncan Aviation’s exterior finish maintenance guidance states that high-quality urethane finishes require a 30-day period before washing and waxing. That is the number worth working to.

NBAA’s Business Aviation Insider, in a piece on painting best practices, quotes a director of painting describing applying a polymer coating 30 to 60 days after the initial paint work is finished. Same order of magnitude, and both figures come from people who look at fresh paint constantly.

To be precise about attribution, because it matters: no coating manufacturer data sheet we have found states a wash or wax wait period. The 30 day figure is MRO guidance, not an OEM requirement. It is well founded and we work to it, and we are not going to attribute it to a paint manufacturer who did not say it.

Why the gap exists

Cross-linking continues well past the point the film is hard enough to fly. During that window the coating has not reached its full chemical resistance or its full mechanical hardness. Which means:

• Cleaners that would be unremarkable on a cured finish can soften or dull an uncured one. ASTM F502, the test for effects of cleaning materials on painted aircraft surfaces, measures softening with a pencil hardness set. That test assumes a cured film.
• Agitation that a cured film shrugs off will mar an uncured one, and the marks are in the topcoat rather than on it.
• Solvents still leaving the film can be trapped by anything that seals the surface, which is the argument against waxing or coating early.

What to actually do in the first month

1. Nothing abrasive. Nothing chemical. If the aircraft picks up dust, a flood of clean water and nothing else. No cleaner, no mitt, no towel.
2. Deal with contamination promptly and gently. Bird droppings and bug remains are acidic and they do not wait for the cure. Soak with clean water, let them release, lift them off without pressure. This is a genuine conflict between two rules and the resolution is water plus patience.
3. Hangar it if you can. Not for the cure, which happens regardless, but to reduce what lands on it.
4. Do not wax, seal or coat it. Wait, and do it deliberately once it is cured. Duncan’s guidance also warns against one-step clean-polish-and-wax products, because they contain abrasive cleaning agents that can scratch the surface, and against waxes containing silicone.
5. Tell whoever is on the ramp. This is the one that actually fails. The aircraft comes out of paint, it looks superb, and three weeks later somebody at an FBO does a courtesy wipe down. Put it in writing to the crew and to the FBO.

After the thirty days

First wash gentle: mild aviation cleaner at correct dilution, plenty of solution, clean media, thorough rinse, dried. Nothing aggressive, no machine work.

Then protection, if you want it, once the finish is genuinely cured. This is the best moment in an aircraft’s life to apply it, because you are protecting a perfect surface rather than locking in an imperfect one. The honest version of the coating decision is here.

Then set an interval based on where the aircraft is going to live, and stay on it. How to set that is here.

Two related cases

Touch-up and partial repaint. The same rule applies to the repaired area, and it is easy to forget because the rest of the aircraft is cured. A crew washing the whole aircraft needs to know a panel is three days old.

Paint protection film. Leading edge film application has its own cure and adhesion timeline and it interacts with the paint’s. Sequence it with the shop rather than around it.

The thing worth arranging in advance

If you have an aircraft in paint now, decide before it comes out who is permitted to touch it and when, and put it in writing. It takes one email and it is the difference between a finish that starts its life perfect and one that gets marred in week two by somebody helping.

We do this routinely with completion centers and MROs, and it is part of delivery and acceptance preparation. If it would be useful to have a one page instruction to hand to your FBO, ask and we will write one for your aircraft.