Cleaning dirty walls Examine the discoloration before you do anything. Moss and green slime often indicate dampness, which means that the basic problem must be put right or the trouble will return. White powder (efflorescence)…

Cleaning dirty walls Examine the discoloration before you do anything. Moss and green slime often indicate dampness, which means that the basic problem must be put right or the trouble will return. White powder (efflorescence)…