What you'll find with soot is that it seem to multiply when you try to clean it. You'll also find that you wont be able to get rid of it all. The cleaning will set the soot into the painted surface, leaving you in need of a paint job(as Steve said). I find that if you don't use something that will seal the soot stain, it will bleed through the final paint. I'd recomend using Brunning's "Grabber Plus" which is easy to use and will hold the soot back from bleeding.