I have done this a couple of times - you can patch it. Biggest challenge with coat it is getting it to adhere.
Here's the trick:
- remove all the loose/nonadhered stuff. I used a putty knife and paint scraper
- Rough up the exposed aluminum bottom underneath and edges of coat it (2-3" overlap) with 100 grit Sandpaper (sanding wheel goes the fastest but you can do it by hand)
- Get the area you want to coat very clean. I scrub first with soap and water then use alcohol to make sure its very clean and dry.
- put on the coat per the directions. Its best to do this in warm weather outside in the sun. I wouldnt even try it less than 60 degrees - takes forever.
- Use a high quality roller with tough/short knap. the cheap ones turn into spackling compound
first time i put the stuff on, i didnt do it right and about 40% came off in a year. The next time I patched it per the above directions - no problems.
good luck
FF