This seems to be a more recent quote from EASA:
"In a new statement, EASA is backing the Airbus view. “Airbus has identified the root causes of the paint issue. Paint process have been further optimized and additional enhancement initiatives have been launched in accordance with these findings,” an EASA spokesperson stated. “We are in contact with Airbus on the matter and are aware that the root-cause analysis has not identified any safety issue that would have an impact on the continuing airworthiness of the affected aircraft.”
It also gives some more detail about the various layers on top of the structural composite, which tallies with many of the statements in this thread - though the number of layers is greater than I realised:
"The A350 paint system consists of multiple layers that cover the carbon fiber structure and the ECF on top of it. The first layers are the so-called basic primers—all of which are applied before final assembly of the aircraft. Several more are added after final assembly in the paint shop: an adhesion promotor, an external primer, intermediate coat, the basecoats and the clearcoat.
The important learning for Airbus from all the troubles is that the way paint is applied to an aircraft has to differ greatly depending on whether the fuselage is made of metal or composites. The A350 is Airbus’ first aircraft that has an (almost) all-composite fuselage. Aircraft are exposed to very high temperature differences, leading materials to expand and contract substantially. As Airbus found out, it gets vastly more complicated when different materials don’t react in the same way. And that is exactly what appears to be happening on the A350: the carbon structure essentially does not expand at all; its so-called thermal expansion ratio is 1. For the titanium fasteners, the ratio is 10. For the ECF, it varies between 15 and 40. And for the primer and paint, it is between 30 and 40.
Airbus says that the “thermal cycling”—many times going from hot to cold and expansion to contraction—can lead to early surface wear and even expose the ECF, which then gets damaged further with no paint protection. One reason why the problem has been so significant for Qatar Airways is that its aircraft are exposed to particularly large temperature variations between cruise flight and time on the ground in the Gulf summer."
https://aviationweek.com/air-transport/ ... -got-worse