I have a wall in the living room that is an external wall. Unfortunately this wall is made up of brease blocks and the oil/damp from these blocks penetrates through the paint to show an outline of each block on the internal side of the wall. I am looking to decorate again, and this time make sure that these blocks dissapear from sight. Has anyone got any ideas? Thought about a sealer but am worried that this one wall will end up a different shade to the other walls in the living room. Appreciate any help!