Another brick in the wall...

Year 7s have been out undertaking a Weathering Safari this week, and finding evidence that the school is actually falling to pieces!
The good news is that the processes that are taking place are very slow, but nonetheless, the action of frost, wind, rain, plants and the students themselves, along with chemical reactions on the surface of the bricks and stones are continuously happening. On our journey around the site, we came across this wall on Hereward.

Here's the presentation we used to provide the background...


And here's the recording sheet


And here's a picture that I took on the way round...

Is it Physical, Chemical or Biological weathering ?