Stone Chimney Flashing

[Housed]

Hello I'm new to this Forum. My house is a stone end terrace, 1890, in Derbyshire. I would like advice on the type of base flashing as a roofer has suggested that after fitting soakers and, I assume , step flashing, he would cover the whole of the flashing with mortar from the roofline to the underside of the stone skirt.
The reason I have contacted a roofer is because when there is a period of heavy wind and rain water will enter the rear chimney and drip onto the fireboard above the fireplace. The rear chimney pot was removed at least 15 years ago and the top was capped. I have a wood burner in the fireplace of the front room and as far as I can tell there is no water ingress.
The roofer also opined that the mid-feather brickwork could be damaged and is allowing water to pass into the rear flue via the chimney pot.

The attached photo shows the area beneath the stone skirt, if that is the correct term. I would welcome any advice on whether covering the base flashing is good practice or not as I have read that the mortar can prevent the necessary movement of the flashing during thermal expansion and contraction, leading to cracking and leaks.

 

[Kearn]

That makes zero sense! I’d doubt his lead capability from that, good leadwork should be weathertight on its own. What is the rationalisation for mortar?

Mortar won’t stick to lead.
Lead expands and contracts in the heat so will crack the mortar.
It’s a daft idea frankly.
Why not just use a strong lime mix in that case.

But I would opt for proper leadwork.

However, I’d want to be sure of my water ingress source before going to that expense.

You have water dripping through a capped off, non vented flue?

Water is highly unlikely to be getting though that pot in any meaningful quantities. And if it did and the feathers have failed, it would be more evident in the used flue than the redundant.

However, there is obvious damage to the stonework at the top do the stack and presumably also the flaunching above. This looks like a nice place for a leak. I’d be starting my spraying here…

 

[Housed]

Thanks for confirming that covering the flashing with mortar is potentially damaging. So is there a procedure for installing flashing that is appropriate for the design of my stone chimney? Do you have any specific links to videos or technical illustrations?
I have attached a photos showing staining around the chimney breast in the rear upper room and also the landing ceiling adjacent to the room. Also a view of the brickwork inside the loft.