Bricks can withstand moisture exposure for a long time, which is why they are often used in outdoor construction. Eventually, though, failed mortar can allow moisture to seep behind bricks, or moisture may make its way in through damage in the bricks themselves. Once this occurs, the moisture compromises the integrity of the bricks.
1. Crumbling Mortar
The mortar between bricks tends to be less durable than the brick material, so it often shows the first signs of moisture damage. Affected mortar may crumble easily. You may be able to scratch or indent it with a fingernail, as well. Once the mortar begins to fail, you will often notice missing mortar around bricks or find mortar dust on the ground at the base of the wall. Fortunately, compromised mortar can be replaced with new mortar.
2. Brick Face Spalling
Spalling occurs when a little bit of moisture seeps into the brick face. It then freezes and expands, breaking off a chip -- or spall -- from the face of the brick. The spalled area can absorb even more moisture and the brick will begin to crumble over time. Hairline cracks in the brick are a common cause, as is moisture seeping into the compromised mortar. Spalled bricks may require replacement, although they can sometimes be sealed against further moisture damage.
3. Loose Bricks
Bricks loosen as the mortar fails, but sometimes the visible mortar surface looks okay. The issue is when moisture gets behind the bricks and begins to crumble the mortar from behind. Each time the moisture freezes, it breaks the mortar and sometimes the brick until you have loose bricks that provide no structural support. The mortar and sometimes the bricks must then be replaced.
4. Crack Formation
Small hairline cracks in a brick can absorb moisture, which is then capable of cracking a brick apart thanks to thermal expansion. Small hairline cracks can be filled with a special resin injector, which will seal the crack and protect against water incursion. Once extensive cracking occurs, though, brick replacement is the only viable option.
Bulging most commonly affects brick retaining walls in the landscape. Water trapped behind the bricks puts outward pressure on the wall so that it begins to bulge forward. It will eventually collapse if not repaired. Your mason will install drainage in the wall. They may also need to rebuild sections if the bulging is severe or if it has damaged the mortar.
Contact a masonry service if you are concerned that water has caused damage to your exterior brick walls.