What causes brick to crumble?
Thursday, February 13, 2020
Both brick and mortar joints deteriorate over time, and repointing mortar for an older brick wall is to be expected. But each other type of damage has a specific cause:
•• Freeze damage happens when water saturates the pores of the brick near the surface and then freezes. Water expands when frozen and this creates surface fractures, like in the photo below.
This type of damage is also called “spalling,” and can be the result of sealing the surface of the bricks with a non-breathable sealant, high-pressure washing, a driving rain before a freeze, and any places where roof water consistently drains down along the wall. To learn more, see our blog post What does freeze damaged brick look like?
•• White powder on the surface of the brick is caused by “efflorescence,” a leaching of salts from the brick by moisture getting behind the brick and migrating to the surface, and is only a cosmetic problem. Go to our article What are those powdery white areas on my brick walls? for details.
•• Rising damp makes bricks gradually crumble and look like they are melting away. Moisture rises up from the ground through porous building materials like the soft brick shown below, which was probably under-fired when manufactured, by capillary action. Freezing temperatures and the salt crystals in the saturated brick cause it to disintegrate over time. See our article What causes the surface of old bricks to erode away into sandy powder? for more on this phenomenon.
•• Long lines of missing mortar are usually caused by corrosion of reinforcing steel “ladders,” used to strengthen a wall, when water seeps behind the mortar, as shown below. Visit our blog What would cause long horizontal lines of brick mortar to fall out? for complete details.
•• Mortar cracks are not necessarily a problem if minor. Mortar is designed to be slightly weaker structurally than the bricks it is bonding. This goes for all types of masonry, including brick, concrete block, or stone, and the logic behind it is that any cracks caused by movement in the wall are easier and less expensive to repair at the mortar joints. A crack in the mortar is called a “bond break” and, because they allow water into a wall and the subsequent deterioration over time, finger-size pieces of mortar will eventually begin to fall out or the mortar will crumble away unless repaired.
••Cracks in both brick and mortar usually mean foundation problems.
Here’s several of our articles about structural problems in masonry walls:
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To learn more about exterior walls and structures, see these other blog posts:
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