Mold, Mildew and Moss
Mold, mildew and moss thrive in shady areas. They will not usually hurt a brick foundation, but they can cause discoloration. A 50/50 solution of bleach and water and a stiff-bristled brush can be used to remove them. Rinse with water after an hour. Moss can be removed by spraying it with a store-bought weed killer.
For brick homes older than a century, you will need to make sure that the mortar you plan to use for repairs is softer than the brick. Today's mortar mixes are often harder than old bricks, and can cause the brick edges to chip or flake.
When replacing areas of old brick with salvaged brick, you must test if they will stand up to the weather. You can do this in one of two ways. First, holding the brick in one hand, tap it lightly with a hammer. If it makes a dull thud, it indicates a soft brick. A metallic ring indicates a hard brick. A more involved test is to soak several of the bricks in a bucket of water and put them in the freezer overnight. Allow them to thaw, then repeat the process two or three more times. If the brick does not crack, you are good to go.
Mortar that is loose, crumbling or cracked means that the bricks need repointing. Scrape out the loose mortar with a screwdriver to a depth of 3/4 inch. Clean with a stiff brush. Matching the color as close as possible, dry-mix three parts of masonry cement with one part sand. Add enough water to make it stiff but not crumbly. Premixed mortar is an even easier option, although you will pay for the convenience. Place some mortar on a trowel and stuff it into the joints with a pointed tool. Make sure that the joint is completely filled. Run a repointing rake with wheels, found at home improvement stores, over the joints to level and flatten the wet mortar to match the old mortar. After the mortar begins to stiffen, brush the joints to match textures. Any clumps of excess hardened mortar on the bricks can be removed by simply striking them off with a trowel.
If the area is not too large, repointing may do the trick. If the foundation is leaking water through the diagonal cracks, however, running fiberglass batts or roll insulation on the inside of the affected wall might be the better option. This may be a good temporary measure, but it will not stop the deterioration. A permanent but more involved and less attractive method is to spread a coat of concrete over the outside of the foundation. It should be about 1/4 to one inch thick.
Bulges in a foundation are not usually a job for the do-it-yourselfer, but a short addition wall can be attempted. You will need to construct a cement bulwark inside the bulging foundation wall. This will require a sloped wall that is at least three inches thick at the top and a good six inches thick at the bottom.