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What's That White, Powdery Substance on My Basement Walls?

Originally posted on Men's Journal | By Max Winters | Last updated Feb 6, 2025 7:00 AM ET

Efflorescence is the white powdery substance you might notice on basement walls, concrete surfaces, or masonry materials. It forms when water moves through a porous material like concrete or brick, carrying dissolved salts with them. Once the water evaporates, the salt deposits are left behind as a chalky residue.

Though it looks like white mold, it’s not inherently dangerous. That said, its presence can indicate moisture issues that you should keep an eye on.

What causes the white powdery substance on basement walls?

The white powder comes from a water-soluble salt. These mineral salts are found in granular materials like concrete, brick or stucco. Though excellent building materials, all of these products are porous and can wick moisture.

When moisture gets absorbed by something like a concrete wall, the water dissolves the composition of salts within the material. As the water migrates towards and out of the porous surface (to your inner basement wall), it carries the salts along. Once the water evaporates, the salts crystallize, leaving a powdery deposit behind.

These surface deposits appear seasonally, when moisture absorption and cold temperatures are more likely.

How to Identify Efflorescence in Your Basement

Color and Texture: A white or light gray powdery substance that’s easily brushed away with your hand.
Location: Typically found on foundation walls, especially near the floor, or on other masonry surfaces exposed to moisture and a significant difference between the interior and exterior temperature.
Moisture Indicators: Areas with efflorescence may also feel damp or cool.
Recurring Presence: If the white deposits are cleaned off but reappear, it’s a strong sign of ongoing absorption of water through the walls.
Streaking: It may form streaks or patterns, depending on patterns of water movement through the material.

Do you need to remove efflorescence?

The efflorescence salt deposits are a cosmetic issue, but they aren't dangerous. Over time they can have a chemical reaction with carbon dioxide and become quite thick. After some time, they'd need a power washer to remove these deposits from building surfaces or concrete slabs, but still, only for aesthetic purposes. Instead, you can simply sweep the surface with a stiff brush, spray the area with white vinegar, and then wipe it with clean water. Regular cleaning can help maintain the appearance of your walls, but addressing the root cause—such as poor drainage, leaks, or insufficient waterproofing—is the best long-term solution.

Can Efflorescence Damage Concrete or Brick Over Time?

The formation of efflorescence crystalline deposits are a sign that your walls have some sort of water exposure. It's worth inspecting any external source of water to see if it is of no concern or if it requires a permanent solution. It's not uncommon for moisture to seep through exterior surfaces when seasonal ground water is high or after humid or rainy weather conditions. But the presence of efflorescence could be a sign of water damage from poor drainage or foundation cracks.

These deeper issues could lead to mildew or mold growth, or structural damage. Installing proper drainage will redirect water and using a waterproofing sealant or moisture vapor will manage moisture levels and the harmless white stains.

This article first appeared on Men's Journal and was syndicated with permission.

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