First of all, I know this is a technology that no one uses or cares about.
I built outposts around stone walls and researched this technology, but the damaged stone walls were not repaired at all.
Also, the tower does not show any aura for the repairing effect, perhaps these two problems are related.
Lastly, I know I am in no position to suggest balance changes, but I feel like this technology should be changed or redesigned. For example, making it also repairing the keeps might make it suddenly very useful and strategically meaningful.