Sometimes when I patch a hole in my covering, the patch does not stay stuck to the original covering after it is cooled off.
Why would this happen?

This doesn't happen all the time, but when it does I've resorted to applying a thin bead of CA around the edge of the patch. this seems to work OK, but it is a bit ugly....(and still leaves the mystery of why it happens)

Do I need to prep the surface prior to putting the patch on? I always clean the area with rubbing alcohol/cotton swabs prior to patching... is this good enough?

I figure the adhesive on the monkote is not activating so I try to turn up the heat a little on my iron, but then it tends to melt the covering...

any ideas?