You may be able to apply a paint or treatment to your external walls to prevent moisture from getting inside the bricks. However, it’s important to bear in mind that these treatments are only effective when the cause of the penetrating damp is porous brickwork, and will not usually be effective against other causes of penetrating damp such as cracks in the brickwork or roof or windows that need to be resealed. You should treat the outside of your house using the damp-proof sealant or paint on a dry day. The treatment is not designed to last forever and you will usually need to redo it around once per year in order to continue experiencing the benefits.