Just found this on the Spandex web-site:
Removing vinyl can be a very time consuming chore. Sometimes this labour intensive cost is underestimated and can severely set one back regarding profit. This is why we thought sharing some of our expertise might be a valuable idea.
1. If possible, try to discover what specific vinyl was used for the application and how long ago it was installed. The older the film, the bigger the difficulty to remove it (more time consuming). Sometimes an invisible topcoat is applied as well to give it a better bonding to difficult profiles.
2. If the brand or type of vinyl is known, check the product specifications in relation to removing the specific vinyl.
3. Different layers of vinyl applied on top of each other can not be separated without causing damage to either one of the layers.
4. When removing small surfaces of vinyl, the preferred tool is a heat gun to gently heat the vinyl without causing damage to the surface it was applied to. Always keep track of the distance between the heat gun and the vinyl. Then take a squeegee to scrape and peel off the vinyl.
5. If larger surfaces of vinyl need to be removed, a heat gun works fine although some professionals prefer bigger tools such as a blowtorch or steamer. Again, mind the surface the vinyl was applied to so not to cause deformations towards the carrier.
6. Removing vinyl works best if you tear it off at a 90° angle. Reflective films tend to come off easier when you pull them close to the surface using a 180° angle.
7. Heat needs to be used in moderation when removing vinyl from double paned windows as the heat between the panes can get hot, causing the window to crack.
8. Cleaning the adhesive of the surface can be achieved using an adhesive remover. When working with chemicals, always wear the proper attire such as a mask and gloves and make sure there is sufficient ventilation in your workspace.
9. If you intend to apply new vinyl, a final cleansing with a surface cleaner is mandatory to be sure there is no adhesive left.