I also noticed the primer seemed to need an extra application or two as it was a little hardier. I just let each subsequent application sit for 15 or twenty minutes and used a plastic scraper and in tougher areas (louvers) I use one of those synthetic wool type scrapper pads dunked in the Citri- Strip. Once the primer strarts to lift it just gets softer and easier to scrape/peel off. I just finished re priming my Cowl and belly pan and couldn't be happier.