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What causes raised white lines of residue on a block wall that are crusty and crumbling?

Wednesday, June 13, 2018

Causes Of Efflorescence On Block Wall

It’s called efflorescence, which is the result of moisture/water inside a wall migrating to the surface and evaporating. Soluble compounds in the concrete block and mortar, such as sulfates of calcium and magnesium, dissolve and get carried to the surface, then are left behind as the water evaporates. Hairline cracks in the mortar were the path of least resistance to the wall surface in the photo above, so efflorescence formed along them. But efflorescence may make powdery splotches on the surface instead.

    Efflorescence can usually be scrubbed off the surface with water, or a mildly acidic vinegar water solution, but the problem will keep returning until the moisture intrusion in the wall has been fixed.

Examples of Efflorescence

    Here’s a couple of photos of moisture accumulation around cracks in a stucco surface the day after a heavy rain and pre-efflorescence.

    This wall surrounded a patio, with a screen enclosure frame mounted on top of it. Moisture entered the wall through mounting holes drilled into the top of the wall for the aluminum frame and fractures around them, along with cracking of the stucco face. A wider view of the area is shown below.

    Here’s a couple of photos of moisture accumulation around cracks in a stucco surface the day after a heavy rain and pre-efflorescence.

    And here’s an example of efflorescence seeping out of both the block and mortar joints at a retaining wall with no stucco finish.

Efflorescence On Brick

    For more examples of efflorescence that appears as splotchy areas on brick, see our blog post What are those powdery white areas on my brick walls?

Rising Damp

   There is also a phenomenon called “rising damp” that cause cause bricks or block to literally melt away over time. See our blog post What causes the surface of old bricks to erode away into sandy powder? to learn more.

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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at for $19.95.
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To learn more about exterior walls and structures, see these other blog posts:

 What are the common problems with concrete block homes?

What is the average lifespan of a house foundation?

What causes vertical cracks in fiber cement siding planks?

 What is the difference between soil subsidence, heave, creep, and settlement? 

How much ventilation is required for the under-floor crawl space of a home? 

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

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

How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem? 

What are the pros and cons of concrete block versus wood frame construction?

What do you look for when inspecting vinyl siding?

Why is housewrap installed on exterior walls under the siding? 

How do I recognize serious structural problems in a house?

What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

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