What Is That White Powder on My Basement Concrete Floor?

Efflorescence forms when water dissolves soluble salts inside the concrete, carries them to the surface, and then evaporates, leaving the salts behind. This process happens when there is moisture in the slab, whether from groundwater, a leaky pipe, or high humidity in the basement air.

The powder can appear as a fine dust, a crusty buildup, or even small crystals. It often shows up in patches near walls, cracks, or areas where water tends to pool. Seeing it means moisture is actively moving through the floor, so it is worth addressing before the condition worsens.

• White or grayish powder on the surface
• Crusty or fluffy texture in spots
• Often worse after rain or snowmelt
• May reappear even after wiping it away
• Usually concentrated near walls or cracks

You can clean efflorescence with a stiff brush and plain water, or a mild cleaning solution if the buildup is stubborn. Scrub the area, then rinse and dry it thoroughly. A shop vacuum can help remove loose powder before you start.

Cleaning alone will not stop the powder from coming back unless you address the moisture source. After cleaning, watch the area to see if it reappears. If it does, that confirms water is still moving through the slab, and you need to look at drainage, grading, or interior humidity.

The most effective way to prevent efflorescence is to keep moisture out of the slab. Check that gutters and downspouts direct water away from the foundation, and ensure the ground slopes away from the house. Fix any leaking pipes or fixtures promptly.

Inside the basement, control humidity with a dehumidifier, especially in warm months. Seal cracks in the floor or walls with a masonry sealer, but note that sealing only works if the moisture source is controlled. If you live in Newark, keep a log of when the powder appears to help identify patterns.