Removing & Preventing White Powder on Concrete Foundation Wall & Floor Surfaces

Published: 04th February 2011
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What it is, How It's Caused, & How to Eliminate It

In our line of business, we come across many homeowners who express concern about a powdery white coating that's appearing on their concrete walls and floors. Often, the homeowner will ask us if the substance is a type of mold or other fungi, if it's harmful, and if there's anything they can do to eliminate this problem and prevent future problems.

What is that White, Flaky Powder on my Concrete?

If the powdery white substance is building up on your concrete surfaces only, then not likely to be mold. Instead, this powder is a mineral salt that's commonly referred to as efflorescence. This builds up on concrete walls and floors in basements and in crawl spaces often, occurring as part of the process of moisture coming from the earth, passing through the concrete, and advancing into your home.

Concrete is porous, and it absorbs water like a sponge. When concrete is being used as part of a crawl space or basement, it soaks up moisture from the earth around it continuously. As it does, the water can pass through to the inside surface of the concrete walls (known as the "negative side"), where it's added to the air inside the building.

As moisture evaporates into the air, it leaves any mineral deposits carried with it behind, which forms a saltlike coating on the concrete. The ugly white powdery buildup is the efflorescence you see on your concrete walls.

How to Clean Concrete Efflorescence

Cleaning efflorescence is best done with a power washer -- you can find one at a local hardware store. Your local store will also have a variety of chemicals that you can use in combination with the washer that will quickly and effectively clean your concrete.

For a simpler method, however, simply combine one part bleach with ten parts water. Use a sturdy push broom, and scrub those walls thoroughly.

Phosphoric acid has also been known to be effective against efflorescence. However, this should be used with extreme care, and it should never be combined with ammonia products, as these two create a poisonous gas when mixed. Phosphoric acid will have the added benefit of being able to eliminate other stains as well, such as those from rust or oil. Be sure to consult with a professional firsthand before using this substance.

Preventing Efflorescence

The best way to stop efflorescence is to halt the advancement of moisture through the walls and into your home. One excellent way to do so is by sealing the concrete on the inside, thereby preventing it from making its way through into your home. This has the added benefit of creating a moisture barrier that will seal away water vapor that would otherwise contribute to the indoor humidity levels of your basement or crawl space.

When choosing a concrete sealer, be sure not to use concrete paint. These types of products are notorious for chipping off the walls over time by both the pressure of the moisture and by buildup of efflorescence behind the coating. Instead of these, it's very important to find a product that will seal the concrete by bonding deep within its pores, creating a solid barrier that prevents moisture from passing through without the long-term blistering, peeling, and flaking associated with waterproof paint and other products.

When you're looking for a concrete sealant, we recommend Concrete Treat: Concrete Sealer and Blanket. When applied, this product creates a glasslike silicate bond deep within the pores of the concrete. The bond seals away humidity and prevents efflorescence buildup on cleaned concrete surfaces. It's usable on both cured and newly placed concrete, and it is also appropriate for outdoor concrete use.

For more information, or to order Concrete Treat, call us at (203) 376-9810 during normal business hours, EST.

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