Several windows have developed cracks in the panes over the past year. These have all been to the front of the house which faces roughly north west. The windows have metal frames fitted into wood, the house was built in the 30s. Nothing has hit the windows apart from the weather.
Any suggestions as to the likely cause of this? Could hardened putty be a factor? Just seems odd but outside my experience growing up when nothing like this happened to my parents windows.
If they are Steel - (Crittal) then any rust forming will occupy more space than the steel and put point pressure on the glass causing it to crack. As to what to do - eitherremove the glass and clean and rustproof the frames before re-glazing or replace the frames. IIRC from a Grand Designs these can be converted for double glazing at a price
There could be several reasons such as rusty frames (galvanising breaking down), screw heads rusting [1] (under the putty), metal clips that holds the glass in position rusting [1] (they take the place of tacks used in wooden frames), temperature variations (especially if the glass is a 'tight fit' in the openings, open sashes twisting and being put under pressure when closed and a multitude of other things that could cause the glass to 'ding'.
[1] As they rust the metals expand and cause pressure on the glass - even though all the frames, clips and screws would have been galvanised when originally fitted, this can (and will) break down over the years causing such problems.
Sorry I can't be more specific (I'd have to see them for that) - but from my experience of repairing these things, I would suggest that if you are starting to have these problems then it may be time to think of replacing them - and you will certainly benefit from reduced heat-loss in the winter (I certainly noticed the difference when I did mine way back in 1990 both in temperature and cost during the winter months).
I once had a 1930s maisonette with crittall windows that were very rusty. I raked all the old putty out and replaced it, treating the metal etc. All looked good. Sitting in the lounge some while after and heard a faint ping. One pane had cracked. This went on intermittently until I had to replace a number of panes. Metal expands and contracts quite a bit with heat and cold. Glass I understand is a supercooled liquid rather than a solid and it gets more brittle with age.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.