Mechanical damage to the coating due to projected small stones/grit (e.g. chippings).
Stones are flung onto the paintwork at varying levels of energy (velocity/size). Depending on the impact force, the top layers and also the other paint layers underneath can be damaged down to the substrate. At the points of damage, humidity will penetrate the coating and lead to corrosion creepback and flaking.
There is no total protection against stone chips. Areas most greatly at risk can be given preventive treatment of additional stone chip and underbody protection (Glasurit 1109-1240/4 Stone Chip and Underbody Protection black) and/or the use of Glasurit 522-111 Softface Additive (4:1 by vol. in topcoats and clears). An extremely scratch-resistant clearcoat, e.g. Glasurit 923-447 HS VOC Clear, scratch-resistant, offers protection against small stone chips.
Stone chips should be touched-up immediately. Refinish using the recommended undercoats and/or topcoats.