how do stop a crack spreading?

Use a glass cutter to cut short perpendicular lines at 5he end of the crack. Be sure it's past the crack. One cut for each crack.
It,will not spread past.

David Shelton
December 2015

hammer

montyson
June 2011

Heidi.
Mr B's right but drilling a hole in a mirrored door will spoil the look of it...
You should seek the help of a windscreen repairman, as they use a Ultra Violate setting glue which is stronger when it sets....I used this glue to repair a glass lampshade, and it's still together.
CHUM

Chumley
October 2009

There are 2 ways you can stop a crack from spreading in glass. The 1st. method is to apply a good grade of super glue into the crack. Loctite super glue is an excellent glue for this. Gently push on one side of the crack. You should be able to see the crack very slightly "open up". Apply super glue the entire length of the crack then release your pressure on the glass.
You can remove excess super glue with nail polish remover that has acetone as an ingredient. If the nail polish isn't strong eneough to remove the excess super glue, you can buy acetone or use a scraper blade to scrape the glue off the mirror surface.
The second (and less preferable) way is to drill the end of the crack with a 1/32" diameter diamond coated drill. If you have never done this, possibly you can get someone who has, to help you out. Drilling the end of the crack nearly always stops the crack from enlarging...Good Luck

Mr.B
October 2009