Bird droppings

In detail

Bird droppings combine three properties that each attack a finish differently. They are chemically aggressive — a mixture of uric acid and, from the digestive tract, alkaline components — so they attack from both ends of the pH scale depending on the deposit. They contain grit, since many birds ingest fine stone, so any attempt to wipe them dry drags abrasive across the surface. And they dry hard and adhere tenaciously. On vehicle clear coat the combination is worst, because heat accelerates the chemistry and a deposit left in sun etches into the film within hours: the deposit washes off and a dished ring remains, which is a polishing problem rather than a cleaning one. The mechanism generalises to every soft or coated surface — limestone and sandstone are attacked chemically, painted timber and powder coating are marked, and glass is the one common surface that is genuinely indifferent. The method follows from the three properties: soften and flood rather than wipe, so the grit floats away rather than being dragged, then wash normally. Speed matters more than product.

Why

• Bird droppings is explained by Why old stains are harder
• Bird droppings is explained by Coating thickness