Quick answer: Efflorescence is the white, powdery, sometimes crystalline deposit you see on concrete, brick, block, or other masonry surfaces. It forms when water moves through the wall, dissolves naturally occurring salts, and deposits them on the surface as it evaporates. The deposit itself is not dangerous, but the moisture driving it can be. Removal of efflorescence without correcting the water source is a cosmetic fix, and the white film will come back.
“Any effort you make to beautify a house with a wet basement or moving foundation will be rendered useless. Ensuring the foundation is perfect is absolutely critical.”, Brady Van Matre, Founder & Owner
We get this call a few times a month. A homeowner notices a white, fuzzy substance along their basement wall and wants to know what it is and whether it’s serious. If that’s you, you’ve got efflorescence. While it’s a common issue in concrete and masonry block foundations, it can occur on any porous surface, such as wood or stucco. While efflorescence is usually white, it can vary in color depending on the salt involved and any associated chemicals. These salts include calcium sulfate, potassium sulfate, sodium sulfate, vanadyl sulfate, calcium carbonate, potassium carbonate, sodium carbonate, and manganese oxide.
The good news is that it isn’t a hazard. Efflorescence is simply salt and can be removed with the right cleaning products and techniques. What you should be concerned about is that it signals a moisture problem in your foundation. Below, we’ll explain how efflorescence forms and how to treat, prevent, and remove it.
What Causes Efflorescence?
Different conditions create efflorescence. When water infiltrates your basement wall, it dissolves water-soluble salts. As the moisture evaporates from the wall surface, it leaves mineral deposits that cause efflorescence crystals to grow. Crystals may be caused by salt-laden soils or contaminated water used to create the wall concrete, mortar, or grout. Natural clays used to manufacture bricks frequently contain alkali sulfates. Although most fired clay bricks today have added chemicals to render these sulfates insoluble, any defects in the production process could create a future efflorescence problem. In cooler climates, freeze-thaw cycles can accelerate the process. Humidity can also affect the appearance of soluble salts. In many cases efflorescence is just an eyesore, but if these crystals grow inside the wall, they can push from the inside out and cause spalling, which is when the surface pops out or peels away. Over time, crumbling and deterioration may result.
On the Colorado Front Range, conditions stack against masonry. Expansive clay soils swell against foundation walls when they take on water, heavy spring snowmelt drives moisture toward below-grade walls, and repeated freeze-thaw cycling pulls salts out faster than in milder climates. Efflorescence tends to be heaviest in the first year after construction and during seasonal transitions when ground moisture is changing quickly. With 25+ years of construction experience across Boulder and Denver, we almost never walk into a home with a foundation problem that also has good grading. Poor grading and downspouts that dump water at the foundation are the most common root causes we find, which is why our crews look at drainage and grading before recommending anything else.
Efflorescence vs. Mold: How to Tell the Difference
Efflorescence and mold are easy to confuse at first glance. Here is how to tell them apart.
Color: Efflorescence is white to yellowish-white. Mold is usually black, green, gray, or brown.
Texture: Efflorescence is dry, powdery, and crystalline. Mold is fuzzy, fibrous, or slimy.
Location: Efflorescence appears on the surface of concrete, brick, block, or stucco. Mold grows on organic materials like drywall paper, wood, or organic dust sitting on masonry.
Water test: Efflorescence dissolves or softens when you spray it with water. Mold does not dissolve and may smear.
If you can’t tell after this check, treat the area as mold until a professional confirms otherwise, and avoid disturbing it without protection.
How to Treat Efflorescence
There are four common ways to remove efflorescence from foundation walls. They all work best when the weather is warm and dry. Before you pick a method, understand what cleaning does and does not do: each of the techniques below removes the deposit itself. None of them stop the deposit from coming back if water is still moving through the wall. Cleaning efflorescence from concrete or masonry is only a permanent result when the moisture source has been corrected first.
Use a Stiff Brush
Stiff brushes can be used to sweep efflorescence away from smoother surfaces. Because it is dry and powdery, be sure to wear a dust mask while sweeping it away. Dry brushing works best on light, surface-level deposits. Heavy buildup or efflorescence that reappears soon after brushing points to active moisture infiltration and a deeper problem worth a professional look.
Apply a Water Rinse
On rougher surfaces, use a pressure washer or garden sprayer to dissolve efflorescence and wash it away. Pressure washers should have the widest-angle tip applied to avoid damaging the wall surface. You may have to re-rinse or brush with this method, as the water can bring more salt to the surface as the substrate dries.
Apply Diluted Vinegar
If you prefer not to use chemicals, diluted white vinegar does an effective job of clearing away efflorescence. Mix a 50-50 solution of white vinegar and water, apply with a stiff brush or spray bottle, and let it sit for five to ten minutes before scrubbing. Rinse thoroughly with clean water when you finish. Vinegar is appropriate for light deposits and is safe on most masonry, but test it on a small, hidden area first.
Use a Chemical Cleaner
Another commonly-used treatment is specialty chemical cleaners. Muriatic acid in a mild solution (usually one part acid to 12 parts water) is one of the conventional cleaners.
Safety first. Muriatic acid is hazardous. Wear chemical splash goggles, acid-resistant gloves, and long sleeves. Work outdoors or in a well-ventilated space, never indoors with closed windows. Never mix muriatic acid with bleach or ammonia-based cleaners. Keep a baking soda and water solution on hand to neutralize any spills.
It is applied as follows:
- Presoak the basement wall to reduce its natural porosity and limit how deep the cleaning solution can penetrate.
- Use several mild individual applications instead of one large and aggressive dose.
- After the cleaning solution has been applied, all residual chemicals need to be thoroughly flushed away with clean water. This step is critical because most cleaning solutions are highly acidic and will erode the masonry if not cleaned away.
- If you don’t have experience handling strong acids, commercial efflorescence removers based on phosphoric or sulfamic acid are a lower-risk alternative that still cuts through most deposits.Our solutions need to work, not need any maintenance, and to be a permanent fix.
