Hello. Need to repaint my fascia which presently has semi-gloss paint on it. I've already scrapped it. I know I should clean the fascia and I've read that I should sand down the paint on it now so the new semi gloss paint will adhere better. I understand that. But what I'd like to know is what grit of sandpaper should I use and how do I know how much to sand the existing paint? I don't want to overdo it but I want to do enough. Thank you.