I used a soldering iron and melted the peices back together. You have to spend a lot of time with it. I had a 12" crack in my bumper and repaired it with a soldering answer and used some sand paper to make it smooth. Most parts on the car that are plastic can be melted back together. BE CAREFUL, IT GETS REALLY HOT. DO NOT BREATHE THE FUMES FROM THE BURNING PLASTIC.
Tip: ABS is the material in mirrors and the crome plated parts are made out of reform easily. So if you break your mirrors in 8-9 peices (like completely apart), it will take about 3-4 hours to reform the plastic with intermediate experience. Use a fan to keep the fumes away, especially ABS fumes. GL. Message me if you have any questions.
You can pick up one of these below from home depot for about $15-$19.