On 28/02/2021 17:06, Chris Hogg wrote:

It looks to me like the builder had some F0 bricks left over and
decided to use them up. Nearby properties may have had better bricks.
Only F2 bricks should be used for chimneys.

Or it is the result of painting.

A bare brick will get wet but also dry out. A brick that is behind a
layer of failing paint may get wet because water runs down behind the
layer of failing paint (a crack where the paint is at the pointing) and
then is prevented from drying out by the paint being an waterproof layer.

A brick wall can prevent water ingress to a house although it does soak
up some water when it rains but, say, as a result of a broken gutter or
dripping overflow pipe the same wall can get much wetter and become
saturated leading to internal damp problems.


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