That beautiful century old brick house that you bought last year looks fantastic, doesn't it? You often find yourself looking at the arches over the windows, the carefully struck joints, and the patina on the brick, and admiring the skill and time that went into the construction of your home.
But there's a problem. Lately you've noticed that the paint is bubbling under the windows in the living room. This generally means that water is getting into the wall, probably because the opening around the window is not well sealed. Regardless of the reason, taking care of the leak is only half the problem. You will need to repair the damaged part of the wall. Repainting usually isn't enough to take care of the problem. Once stucco or plaster and lath has become so damp that it causes paint to bubble, it will likely remain damp.
If your house was built around the turn of the century (early 1900s or late 1800s) there will probably be 4 inch by 8 inch unglazed terracotta utility block behind the brick.
The first step is to remove the damp plaster and lath or stucco attached to the utility block. If the inside wall is plaster and lath, you can score the plaster with a utility knife, and remove it from the lath using a carpenter's chisel along the scoring. If the plaster is damp, very little force will be needed to remove it. You should start with an area about a foot clear of the bubbled paint on all sides.
Once you have reached dry lath, you will need to remove the lath in the damaged area. Again, a carpenter's chisel can be used to break the lath, after scoring it. Alternatively, you may have stucco over utility block. If this is the case, the damp stucco will slough off when hit with a hammer and chisel. It should take little effort to remove damaged stucco.
After you've removed the stucco, leave the block exposed for a day or so in order to dry.
Once the block is dry, apply tile grout to the block to create a smooth surface that can be sealed. When the tile grout has set, use a product like Zinsser WaterTite to seal the inner surface of the wall.
When the sealant has dried, you can cut drywall and glue it to the sealed surface in place of the plaster and lath or stucco. Use drywall mud to blend the drywall into the surrounding wall. Prime it and repaint the wall.
If this seems a bit daunting, you can always hire a contractor with experience repairing old houses