Crack in Window Pane

[adam81]

Hi,

I've had a crack appear on the inside pane of a double glazed window recently.

I did some work on the ground floor below this recently and removed an old window and replaced it with a door. All with catnic's so properly installed. (Hopefully)

I wonder if this though has still caused the crack?

I've removed the beading at the top of the pane in question and can run a piece of paper all along the top of the glass between the PVCu frame it is in suggesting the frame has not bowed down and is not compressing on the pane. To my mind this indicates that the brickwork has not compressed onto the frame. When the PVCu windows were installed before I bought the house no lintels were used on the outside leaf anywhere.

On the ground floor there is evidence of smiling bricks across the top of these windows, as there was in the window I removed downstairs.

There is no cracks or visible movement in any of the brickwork that has been alerted recently. Also there are no new cracks on the inside of the wall, or in the reveals itself which was newly plastered about 2 years ago.

The only other factor is recently we have been using a black out blind in that room, and after Sunday when the sun was out the crack did get bigger. In principle I guess the heat could cause the already crack to get bigger but could this have been a cause in the first place?

Do panes have a shelf life occasionally? Not sure how old they all are but I expect pretty old.

I don't want to order replacement glass only to find it happens again, and therefore needs a new frame and lintel installing.

I realise it's difficult but any previous experience would be good.

I can take photo's put from ground level will not show much I fear.

edit..
A bit of searching as found this..http://www.thewindowman.co.uk/explode.htm so the black out blind would only amplify this scenario I guess.

 

[foxhole]

Any weakness in the glass or construction could cause the crack with the help of a little heat/cold movement.

 

[adam81]

From the link..

..The pane of glass subjected to the thermal stress cannot cope beyond a certain amount of deflection, and it will suddenly crack along the whole length of the unit, always along the long length, or it can suddenly shatter altogether.

Mine has not cracked in this way, rather it started at the middle of the pane at the top and has slowly worked its way down and to the side finishing about half way down the pane..

 

[crank39]

I was just going to post the same link, i have it saved as a favorite and is a good reference for posts such as your, he explains it better than i ever could

 

[adam81]

So you would guess it is heat rather than the brick work causing the issue? What with the gap still between the pane and the frame?

 

[crank39]

Yeah all day long, if you can see a 5mm gap around the glass, no bowing or cracked sealant then its thermal, i see it quite often on my travels, the website confirms there is an issue also