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. 

[Sparrowhawk]

@Nickfromwales here you go - there's not a single screw on either side of the bay window to tie it into the masonry. It hasn't gone anywhere in the 20 years it's been installed, but from what you say that's not how it's supposed to be.

 

There's two steps here then:

• Getting through the winter with it weathertight - whatever bodge will do
• Making sure when the bay windows are replaced in a year or two that they're installed properly

 

Because the bricks have been cut at 45 degrees for the original wooden windows and are "well weathered" I can understand why they haven't bashed long screws through because it feels like there's not that much for them to bite into.

 

 

 

 

[Nickfromwales]

They could have concrete screwed some treated battens into the brickwork, and then screwed into that. 
 

There’s always a way to do a job to the best possible outcome. 
 

Or. Cut corners, grab the money, and shoot off.   

[Sparrowhawk]

Oh yeah, that would have worked 🤣

 

I guess if fixing now, a timber packer between window and brick and then screw through it would do. With the window frame in place screwing a batten on would be a pita