Ok so my brother got a new house and there was some wall problems that needed painting. He got Dunn-Edwards Paint interior and exterior. Well he accidently used exterior paint on the interior walls then he tried to go over it with interior paint. It didn't work to well. And he doesn't know how to fix it. Please help.! Oh and the exterior paint is Spartashield flat and the interior pair is Suprema flat. Please please please help.