[DoubleGlazing]

I used to work in a building that was once a factory, the room I was in was once a break room. For years workers would come in for their lunch and lean back against the walls. Years of (probably Brylcreme'd) heads being placed against the walls led to a situation where no amount of painting would cover it up. All these little brownish-grey spots appearing on the walls a few hours after each painting.

Then one day the room was properly refurbished and management paid the decorators to put in a special barrier layer and the grease spots finally dissipated.