The truth about bird droppings – not corrosive, it seems
May 4, 2011 at 1:00 pm By Anthony Lim Filed Under Cars
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So you’ve parked your car under a tree. Useful shade, you think. And then you come back hours later to find lots of random artwork on your car, courtesy of some feathered friends. Much later, when you try removing them, you find that you’re left with the telltale signs of where the offending material had been, even though the residue has been removed.

Common belief is that it’s the nasty stuff in bird droppings that do the damage to the paintwork, in the form of a blotchy, faded spot. Well, new research from Brit car care company Autoglym suggests that the familiar sight of car bodywork ‘etched’ by bird droppings are not the result of any corrosive property in the deposit. Rather, the damage result from the paint lacquer contracting upon cooling and moulding to the uneven texture of the hardened deposit.

Apparently, as paint lacquer warms – under direct sunlight, for example – it softens and expands. At the same time, that heat dries and hardens any bird droppings on the surface. Autoglym’s researchers discovered that as the paint lacquer cools, overnight for example, it contracts, hardens and moulds around the texture of the bird dropping.

To the naked eye, this moulding at a microscopic level appears as dulled or etched paintwork once the surface is cleaned of the residual dropping. The light’s reflection is interrupted by the imperfect surface, unlike the undamaged paint surrounding it, which gives a clearer reflection.

The company says that tests with strongly acidic, neutral and strongly alkali bird dropping substitutes highlighted negligible differences in the damage caused, but differences in paint damage were noted when the substitute bird deposits had varying degrees of grain-to-liquid content – a grainier texture caused greater light distortion (dullness) when the paint moulded around it.

Wax and polish treatments – that protect against chemical attack from acid raid and UV sun damage – provide limited protection from the paint moulding to bird droppings, although they will make them easier to remove. The longer the deposit remains on the bodywork, and the higher the temperatures, the harder the dried deposit will be, and the greater the propensity for the paint lacquer to mould to it as it cools.

So, the only way to prevent the paint becoming noticeably tarnished is to carefully remove deposits as swiftly as possible, preferably with a moist cloth. And there you have it, the truth of the matter, no shit.