When it rains sometimes it drips water along the top interior window frame. One one occasion water collected behind the interior wall paint and formed a water balloon. I took a guess at how the water was entering and corrected it. But even after that I still have water dripping from the top window frame.
I like the lime idea. Lime comes in many forms (e.g. quicklime, hydraulic lime). I’m not sure I’d be keen to work with the stuff that needs a complex number of steps with a mixer that can withstand heat. Suppose I buy “white lime” (which is marketed as a whitewash for trees as an anti-pest control, and for cosmetic changes on brick walls). Will that do the job? I think I simply mix it with water. How do I bond it? With PVA?
(edit) Since I guess you speak French, perhaps you can tell me if this stuff is right for the job:
^ I have some of that stuff already on-hand but it was opened ~14 months ago, so it might be oxidized into chalk. I’m not sure how to test to see if it’s still usable.
It appears the #Cantillana varieties of lime render are simply rendered on with no bonding steps or additives.