This idea is mainly based around the self-healing concrete idea that has appeared in the past and scientific posts have been made about the self healing concrete using bacteria to self heal cracks. What my question asks is whether or not this could apply to a vertical structure such as a castle wall and whether it would be practical.
Recognizing that the bacteria in order to produce the limestone used to fill the cracks, water is needed in order to activate, I thought perhaps a rain or mist would work. Granted this would mean that a castle with this sort of function would only self heal with applied water or would be dependent upon the weather but still my thought process.
Another requirement for the bacteria is the sugar or food component which the website I provide uses calcium lactate so I suppose part of my question is whether or not this would work as well for castle walls.
Also to clarify, the healing component I'm trying to apply for this question is the outer defensive castle walls of this hypothetical castle that is able to self heal using mainly impressive science, or at least as scientifically based as possible before I resort to magic into this idea specifically.
https://www.cnn.com/2015/05/14/tech/bioconcrete-delft-jonkers/index.html
Thank any and everyone again for providing any sort of answer/input.
(Edit)
The castle I have in mind would be made of concrete at least partially and I do believe this is an example of a castle that is made of concrete and some parts reinforced concrete. Concrete itself wouldn't require steel as I've come to understand it.
https://buckslib.org/the-mercer-museum-castles-made-of-concrete/
Would it still be possible for a concrete castle above ground and not in the water to employ this sort of idea hypothetically?