When Bricks Sweat: How to Get Rid Efflorescence on Your Siding

By James Fitzgerald

September 28, 2026

If you've noticed a white, chalky residue spreading across your foundation walls, brick steps or basement block, you're looking at something called efflorescence. The buildup is common on masonry surfaces exposed to moisture. While the deposits themselves are mostly cosmetic, they signal that water is moving through the material and depositing minerals on the surface as it evaporates.

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Left unaddressed, the moisture behind efflorescence can lead to more serious problems, including spalling (where the face of the brick or block flakes away), alkali staining (discoloration caused by alkaline salts migrating to the surface) and ongoing mineral deposits that become harder to remove over time.

What Is Efflorescence?

Efflorescence is a white, powdery deposit that forms on the surface of masonry materials such as brick, concrete block, poured concrete and natural stone. It's composed primarily of calcium carbonate and other soluble salts that are naturally present in cement, mortar mix and some types of stone.

What Causes Efflorescence?

It begins when water enters the masonry through rain, groundwater or condensation and dissolves the soluble salts inside the material. As that water migrates to the surface through capillary action (the tendency of water to move through small pores and gaps in a material), it evaporates and leaves the dissolved minerals behind as a crystalline residue. The result is the white bloom that appears on walls, foundations and other exposed masonry.

Several related terms describe variations of the same process. “Saltpetering” and “leaching” both refer to moisture drawing salts out of masonry. Subflorescence occurs when the salts crystallize below the surface rather than on it, which can generate enough pressure inside the pores to cause spalling. “Rising damp” describes moisture that travels upward from the ground through a foundation wall by capillary action, often driven by hydrostatic pressure, which is the force exerted by standing or pooling water against a below-grade surface. Each contributes to mineral deposits on or within the masonry, and all point back to moisture intrusion as the underlying cause.

Efflorescence can appear on both new and old masonry. On new construction, it's often temporary as excess moisture from the curing process works its way out.

Does Efflorescence Damage Concrete or Brick?

On older structures, recurring deposits usually indicate an ongoing moisture source that, if left unaddressed, can lead to spalling, persistent staining or water damage behind the wall.

Efflorescence Vs. Mold

Efflorescence and mold are not the same. Efflorescence is just mineral deposits. Left untreated, it can cause damage, but it's easy to clean. Mold is an organism that grows in damp places. You can also clean it, but you often need to kill or mitigate it to prevent it from coming back. Mold damage is often more severe than efflorescence.

How to Remove Efflorescence From Bricks or Foundation Blocks

Things You'll Need:

Stiff-bristle nylon brush or masonry brush
Garden hose with spray nozzle
Bucket
Muriatic or hydrochloric acid, or commercial efflorescence cleaner
Plastic or acid-resistant spray bottle (if necessary)
Rubber gloves
Safety goggles
Plastic sheeting
Pressure washer (optional)
Wet/dry vacuum (optional)

1. Dry-Brush the Surface

Start by scrubbing the affected area with a stiff-bristle nylon brush or masonry brush. Many light efflorescence deposits, particularly on newer masonry, can be removed with dry brushing alone. Work in firm, overlapping strokes and brush the loosened powder away from the wall rather than grinding it into the pores. If the deposit comes off easily and the surface looks clean, no further treatment may be necessary.

2. Rinse the Area

If dry brushing doesn't fully clear the residue, wet the surface thoroughly with a garden hose before applying any cleaning solution. Pre-wetting serves two purposes: it prevents the masonry from absorbing the cleaner too quickly, and it helps keep the acid or cleaning agent concentrated on the surface where it can dissolve the mineral deposits rather than soaking deeper into the material.

3. Apply the Cleaning Solution

Two common options for chemical removal are muriatic acid (a diluted form of hydrochloric acid) and commercial efflorescence cleaners. Muriatic acid diluted to a ratio of roughly one part acid to ten or twelve parts water is the most commonly used treatment for efflorescence on brick and concrete block. Commercial efflorescence cleaners are typically less aggressive, which makes them a better choice for polished or lightly textured surfaces where acid could etch the finish.

If you're using muriatic acid, pour the water into the bucket first, then add the acid. Never the reverse, as adding water to acid can cause a dangerous splashing reaction. If you're using a commercial cleaner, follow the manufacturer’s dilution and mixing instructions.

Regardless of what you use, wear rubber gloves and safety goggles throughout the process and protect nearby plants, metal fixtures and finished surfaces with plastic sheeting. Muriatic acid, in particular, is corrosive and produces strong fumes, so work in a well-ventilated area.

Apply the diluted solution to the pre-wetted surface using an acid-resistant spray bottle or by brushing it on directly, then let it sit for three to five minutes. You may see light fizzing as the acid reacts with the calcium carbonate deposits. Scrub the area with your masonry brush, then rinse thoroughly with clean water from the hose.

Repeat the above steps if any heavy buildup remains.

4. Address Heavy or Widespread Deposits

A pressure washer can help remove thick efflorescence from large areas such as retaining walls or full foundation faces. Use a fan-tip nozzle and keep the spray at a consistent distance to avoid gouging the mortar joints. Start at a lower pressure setting and increase only as needed since high pressure can drive moisture deeper into the wall and worsen the cycle. For indoor surfaces such as basement block walls, a wet/dry vacuum can be useful for collecting rinse water and loosened residue.

5. Let the Surface Dry Completely

After cleaning, allow the masonry to air dry for at least 48 hours before any further treatment. The surface needs to be thoroughly dry so that protective sealers can bond properly without trapping moisture beneath the coating. If efflorescence reappears during the drying period, moisture is still migrating through the wall. Check for common sources such as poor drainage against the foundation, cracks in the masonry or condensation in the space behind the wall.

The prevention section below covers moisture sources, sealing options, and other long-term measures in more detail, but the underlying problem should be resolved before any coating is applied.

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Does Efflorescence Ever Really Go Away? How to Prevent It From Coming Back

Removing efflorescence treats the symptom, but deposits will return unless you address and manage the moisture source. Prevention works on two fronts: reducing the water that enters the masonry and limiting its ability to carry salts to the surface.

Start with drainage and grading around the foundation. Gutters should direct water away from the base of the structure, and the soil grade should slope away from foundation walls so that rainwater and snowmelt don't pool against the masonry.

In basements and crawl spaces, check for cracks or gaps where water seeps in and repair them with hydraulic cement or an appropriate masonry patching compound.

Interior moisture is also impactful. Condensation on cool foundation walls can produce enough moisture to trigger efflorescence from the inside out. Several measures help reduce the conditions that keep masonry wet, including:

Running a dehumidifier in damp basements or crawl spaces to lower ambient humidity
Improving ventilation by opening basement windows or adding a vent fan so moist air doesn't stagnate against foundation walls
Insulating cold-side walls by adding rigid foam insulation to interior foundation walls to reduce condensation on the cold surfaces
Fixing plumbing leaks near foundation walls before they saturate the masonry

Dryer vents and exhaust fans should discharge to the exterior, not into enclosed spaces. Even small, consistent moisture sources can sustain efflorescence cycles if they're left in place.

Applying a breathable siloxane sealer to the exterior face of the masonry is one of the more effective long-term preventive measures. Siloxane-based sealers penetrate the pores of the brick or block and repel liquid water while still allowing water vapor to escape, which prevents moisture from becoming trapped inside the wall.

This breathability is important because a sealer that traps moisture can accelerate subflorescence and spalling rather than prevent them. Apply the sealer to clean, dry masonry according to the manufacturer's instructions, and plan to reapply every several years depending on exposure and product specifications.

For new construction or repointing work (replacing deteriorated mortar joints between bricks or blocks), using low-alkali mortar and storing masonry materials off the ground and under cover before installation can reduce the amount of soluble salt available in the wall from the outset. These steps won't eliminate efflorescence entirely, but they limit the raw material that moisture has to work with.

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