Did your friend ever try skipping primer in a dry climate? My buddy out in Arizona thought he could just slap a light beige over his old tan wall without it, said the paint coverage looked fine at first. Then their summer monsoon season hit, and after all that humidity the whole surface started bubbling up near the windows within a year. He ended up having to strip it all back down and start over, which was a huge mess. Seems like skipping that step really depends on your local weather messing with the walls. Has your friend in a humid place ever had it work out for them?