Can bird droppings damage glass?

Nothing in the National Glass Association's cleaning paper, the PGT, CGI and WinDoor care instructions or Pilkington's bulletin for its self-cleaning glass says that bird droppings damage, etch or permanently mark glass. That silence is the finding, and it is not a statement that droppings are harmless either: no source read tests it one way or the other.

What NGA's quick-reference list does carry is two rules that read on a dropping as on any other deposit: “DO NOT allow splashed materials to dry on the glass surface” and “DO NOT allow dirt and residue to remain on glass for an extended period of time.” Neither names bird droppings, and neither gives a number of hours. Whether love bugs can be cleaned off windows sets the same splashed-materials rule beside UF/IFAS's findings for another deposit that lands on glass.

Pilkington's technical bulletin ATS-166, written for its Pilkington Activ self-cleaning coated glass, says that to remove deposits of dust or large lumps of bird droppings, which “can take excessive amounts of time to break down,” that glass “can be simply hosed down with clean water” from the top of the window down and left to dry naturally.

That hosing line belongs to that one coated product. PGT, CGI and WinDoor list “a power washer or garden hose” among the items not to use on their windows, screens, doors or hardware, warning that “these improper tools may void your warranty and/or damage your products.” A power washer is the machine used in pressure washing, so that method is ruled out on those products too. Whether windows can be cleaned with a garden hose takes up that conflict on its own; each maker's instruction stays with its own product.

PGT, CGI and WinDoor tell owners to “wash your glass frequently to remove surface dirt and prevent stains,” and NGA's rule not to let dirt and residue remain for an extended period sits beside it; neither is written about droppings in particular. The published method for exterior glass in NGA's paper, a soak followed by a squeegee, carries no separate step for droppings.

Whether a dried deposit has already marked a specific pane, or is still sitting on top of it waiting for a wash, is not something a description settles. That call belongs to a glass professional looking at the glass, the same limit that applies to spots that stay after regular window cleaning.

Droppings are one deposit among several. Whether pollen sticks to windows covers another that lands on glass, and whether window cleaning helps a storefront covers the glass on a shop front.