The culprit is almost always high moisture content in the brick, especially at the face. And the specific delivery system of the wetness could be 1) sprinklers hitting the wall, 2) rain rolling off the edge of a short roof overhang with no gutters and splashing back onto the wall, 3) a plumbing leak, or 4) moisture rising up from wet ground—being wicked upward by capillary action (rising damp).

    If the color is dark green or black and the surface can be scraped off, then it is a fungal growth. A white powdery surface means it’s efflorescence, which happens when the salts in the brick become wet and get pulled to the surface, then dry. See our article What are those powdery white areas on my brick walls? for more on this phenomenon. 

    Other colors, such as yellow and red ochre, are also the result of dissolved minerals migrating to the surface and drying into powder. Rust from reinforcing steel ladders in the mortar joints can also cause staining and cracking along the mortar line. Go to What would cause long horizontal lines of brick mortar to fall out? for more details.

    Rising damp occurs when there is no water-stop material between brick courses, such as a metal or lead flashing, near ground level to stop the upward movement of moisture coming from the soil. In some cases, it can cause brick to disintegrate and crumble away. Read our article What causes the surface of old bricks to erode away into sandy powder? for photos and details. 

    Examples like the one shown at the top of the page are most likely a comabination of sprinkler overspray and rising damp. 

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Here’s links to a some of our other blog posts about BRICK:

• What causes stair-step cracks in a block or brick wall?

• What causes a horizontal crack in a block or brick wall? 

• What does freeze damaged brick look like? 

• Are brick houses hotter in Florida?

• Is a brick house sturdier than a wood frame house? 

• How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

• What causes a vertical crack in an exterior concrete block or brick wall? 

• Why is my brick wall cracking?

• What causes mortar cracks?

• What is the average life expectancy of brick?

• Which is better: vinyl or brick manufactured/mobile home skirting?

• How do termites get into a brick house?