Upon further investigation (it wasn't my project) I have discovered that the facts of the story are this:

Keim mineral paints were specified for coating of precast concrete cladding panels to a 25+ storey office tower.

The concrete was cleaned, but bird shit stains proved to be intractable on the window sills and spandrels.

The subcontractor (who was ostensibly the agent for Keim mineral paints at the time and thus should have known better) applied the paint directly over the bird shit stains.

It appears that the potassium silicate reacted with the bird shit, and thus the stain read through the paint system.

In the end, a primer was applied over the bird shit stains, and the problem was solved thus.

I have looked for photos but cannot find any in our filing system, so must apologise for that.

Just goes to show you should do your research, not just rely on your memory of conversations.

Hope this helps

david