Husband painted a wall in our front room today and this weird rectangle has popped up like a big wide screen tv mark! Any ideas what this could be? Will we need to seal/use some kind of stain cover? So bizarre. It’s an internal wall between living room and kitchen. Any advice would be much appreciated. Thanks!
Guess it's still wet as someone painted wall square white for projector and that has sealed that area so paint is taking longer to dry. Maybe that area has been painted over so you were unaware but hanging wet