Bay window, thermal cracking

[Sparrowhawk]

Opening up the side of a bay window, I could see daylight where the mortar had cracked away from the window. Water weeped in when it rained. I filled the internal gap with closed cell expanding foam, but I want to seal it from the outside as well.

 

Last autumn I wiped CT-1 over the cracks which kept the water out for the winter, but it didn't withstand the expansion cracking in the summer heat. What can I do for a longer-term fix? Silicone might stretch enough but I want to be able to overpaint.

 

And with the 135° angle where the window meets the wall it's not like a nice fillet of sealant will fit.

 

Do I need to pop some plastic capping over this and stick it in place either side? of the joint?

 

 

[Nickfromwales]

Can you post some wider aspect photos plz?

 

Id say you need to tie in some masonry on the interior, and then screw the frames far better to arrest all that cracking.

 

This simply doesn’t have anything to fix into so that needs to be done properly before sealing up again.