I've just redone the flashing seal with the brickwork on my flat bay window
roof. The depth inserted is about 15mm so a bit less than recommended.
I've directed a hose at highish pressure along the joint for a few minutes,
but it still leaks. I've simulated I guess an attrocious storm but that's
not really acceptable I don't think. Can I treat the mortar I've applied
with some silicon treatment to reduce ingress further? Or what?

TIA,
Mike W