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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Efflorescence:
Causes, Removal
& Prevention

What the white deposits on concrete, block and pavers mean, how to clean them without making it worse, and how to stop them coming back.
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  • Exterior block, brick and retaining walls
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Step 1 of 3
3
Conditions needed at once: salts, water, and a way for water to move
CMHA TEK 08-03A
5–10%
Muriatic acid solution for stubborn deposits (2% on colored units)
CMHA TEK 08-03A
4 sq ft
Largest area to acid-treat at one time before scrubbing
CMHA TEK 08-03A
Up to 10 yrs
Service life of a clear water-repellent treatment
CMHA TEK 08-03A

Efflorescence is the white, powdery or crusty deposit that shows up on concrete, block, brick and pavers. It is salt left behind when water moves through the masonry and evaporates at the surface. On its own it is mostly cosmetic. What it tells you is not: water is getting into the concrete and moving through it. Clean the efflorescence without dealing with the water and it comes back, and if you coat over it, the coating is what fails.

Quick answer

Brush it off dry first; most efflorescence is water-soluble and much of it weathers away on its own. If it persists, rinse in warm, dry weather. Hard white crust that does not brush off is usually calcium carbonate and needs a dilute acid or a proprietary efflorescence cleaner on a pre-wetted surface, in small sections, then a thorough rinse. Then find the water source: missing flashing, a downspout, soil against a wall, rising damp in a slab. Seal with a breathable water repellent only after the surface is clean and dry.

What's in this guide
  1. 1What efflorescence is, and why it forms
  2. 2Identify it and find the source (tool)
  3. 3How to remove efflorescence
  4. 4Acid dilution and cleaning planner
  5. 5Preventing efflorescence
  6. 6Efflorescence and floor coatings
  7. 7FAQ
The basics

What efflorescence is, and why it forms

The Concrete Masonry and Hardscapes Association (CMHA, formerly NCMA) defines efflorescence in TEK 08-03A as a deposit of soluble salts and bases, usually white, on the surface of masonry or concrete. The Brick Industry Association's Technical Note 23A says the same thing about brick. Both list three conditions that have to happen together:

  1. Soluble salts in or touching the masonry

    Sodium, potassium and calcium compounds from cement, mortar, grout, soil, deicers or seawater. BIA lists sulfates and carbonates of sodium, potassium, calcium, magnesium and aluminum as the most common.

  2. Water to dissolve them

    Rain, groundwater, irrigation, condensation, or leftover construction water.

  3. A force to move the solution

    Evaporation at the surface or hydrostatic pressure pushing water through the concrete.

Take away any one of the three and efflorescence stops. In practice, water is the only one you can control.

The calcium carbonate problem

Some efflorescence is simple soluble salt that brushes or rinses off. The stubborn kind starts as calcium hydroxide, a byproduct of cement hydration. It is soluble, so water carries it to the surface, where it reacts with carbon dioxide in the air to form calcium carbonate, which is only slightly soluble. That is why some deposits wash away in the next rain and others build into a hard white crust or a "lime run" streak below a crack.

Why it is worse in winter

TEK 08-03A notes that efflorescence shows up more in cooler, wetter months, because slow evaporation leaves the salts on the surface. In summer, water evaporates fast enough that less salt is deposited on the face. BIA calls efflorescence within the first year of construction "new building bloom", normal drying of construction water, usually uniform across a wall. It typically fades on its own.

When it is not harmlessBIA notes that efflorescence is usually not harmful, but when salts crystallize inside the masonry instead of on the face (called cryptoflorescence or subflorescence) they can build enough pressure to spall the surface. If you see flaking along with the white deposits, read our spalled concrete repair guide.
Tool 1

Is it efflorescence? Find the water source

White deposits are not always efflorescence, and the pattern usually points straight at the water. Two quick tests help: a drop of water (soluble salts dissolve and disappear) and a few drops of vinegar (calcium carbonate fizzes). Mold smears and often has color; chalking paint rubs off on your finger as paint-colored powder.

Identifier

Efflorescence identifier and source finder

Matches the deposit type to a removal method and the location and pattern to the most likely water source.

Also seeing
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Most likely water source
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Start removal with
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Urgency

    Cleaning

    How to remove efflorescence

    Always start with the gentlest method and work up. TEK 08-03A lists them in order: dry brushing, then flushing with water, then light brush sandblasting, then dilute acid. BIA adds that water washing should only be done in warm, dry weather, so the surface dries quickly and does not pull more salt up.

    MethodAggression (1–5)RemovesRisksUse on colored units?
    Dry stiff-bristle brush1Loose soluble saltsMinimalYes
    Brush plus water rinse2Soluble saltsAdds water; do it in warm, dry weatherYes
    Proprietary efflorescence cleaner3Salts and light carbonateFollow label; test a patchPer label
    Light brush sandblast4Stubborn depositsCan roughen or open the surfaceTest first
    Dilute muriatic acid, 5–10%5Calcium carbonate crustEtches, can blotch color; hazardousOnly at 2%
    High-pressure washing4Surface depositsDrives water in; can bring it backLow pressure only
    Sources: CMHA TEK 08-03A (method sequence, 5–10% and 2% acid, 4 sq ft sections, pre-wetting) and BIA Technical Note 23A (dry brushing, warm dry weather). Aggression scale is our ranking. Click a header to sort.

    The acid method, done safely

    1. Test a hidden spot

      Acid can lighten or blotch colored concrete and pavers. Try a small area first and let it dry before you judge it.

    2. Pre-wet with clean water

      TEK 08-03A calls for saturating the surface first so the acid stays on top instead of soaking in.

    3. Work in small sections

      Treat no more than about 4 sq ft at a time, wait about 5 minutes, then scrub with a stiff brush.

    4. Flush thoroughly

      Rinse with plenty of clean water so no acid or dissolved salt is left in the surface.

    5. Wait before sealing or painting

      TEK 08-03A suggests letting the surface weather for at least a month after acid cleaning before painting.

    SafetyHardware-store muriatic acid is about 31.45% hydrochloric acid. The HASA safety data sheet calls for gloves, eye and face protection, and rinsing skin or eyes with water for 15 to 20 minutes after contact. Always add acid to water, never water to acid, and protect plants, metal and glass nearby.
    Tool 2

    Efflorescence cleaning and acid dilution planner

    Mixing ratios get garbled on job sites. This planner turns the TEK 08-03A percentages into parts of water per part of commercial muriatic acid, works out how much of each to mix for the area, and how many 4 sq ft sections the job breaks into.

    Planner

    Acid solution and section planner

    Solution % here means percent commercial muriatic acid by volume (10% = 1 part acid to 9 parts water). Volume needed = area / coverage rate you enter. Sections = area / 4 sq ft.

    Use the cleaner label or your test patch
    Wet, apply, wait 5, scrub, rinse
    —
    Acid : water
    —
    Gallons of solution
    —
    Muriatic acid needed
    —
    4 sq ft sections / time

    If the planner says you need a lot of acid, stop and reconsider. Large areas of efflorescence almost always mean a large water problem, and cleaning will not last. Dry brushing every few weeks through one wet season while you fix the water is often the smarter path.

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    Prevention

    Preventing efflorescence

    Since salts are already in every cementitious material, prevention is about water. TEK 08-03A's recommendations for masonry walls include flashing at parapets, lintels and the base of walls, tooled concave or V-shaped mortar joints on weather-exposed faces, integral water-repellent admixtures in new units and mortar, and clear surface water repellents, which it says can be effective for up to 10 years.

    Basement walls

    Keep groundwater off the wall

    Regrade so soil falls away, extend downspouts, and repair cracks. On the outside, a waterproofing membrane; on block walls, a sound parge coat. Our parging guide covers that. For bigger leaks see basement waterproofing cost.

    Exterior walls

    Stop water at the top and joints

    Caps, copings, flashing and sealed joints. A breathable masonry sealer (silane or siloxane type) cuts water absorption without trapping vapor.

    Pavers and patios

    Good base drainage, then seal

    Efflorescence on new pavers is common and fades with time. Clean, let it dry, then apply a paver sealer once the bloom stops.

    Slabs

    Vapor retarder and drainage

    Slabs on grade without a vapor retarder pull ground moisture up all year. That cannot be fixed from the top with a sealer alone; it needs a coating system designed for moisture.

    Do not trap itA non-breathable paint or sealer on a wall that is wicking water can push the salts to crystallize behind the film. The film then blisters and flakes. If water is still moving through, use a breathable treatment or fix the water first.
    Coatings

    Efflorescence and floor coatings

    This is where efflorescence costs real money. A garage or basement floor with white deposits is a slab with moisture moving up through it. Put an epoxy, polyaspartic or polyurea coating on top without addressing that, and the water and salts collect under the film. You get blisters, white haze under clear coats, and coating that peels in sheets. We see it most on older slabs poured without a vapor retarder.

    Test before you coat

    • Plastic sheet test (ASTM D4263): tape an 18 x 18 in sheet of plastic to the slab, wait at least 24 hours, and look for darkening or condensation. It is a yes or no screen, not a number.
    • Calcium chloride test (ASTM F1869): measures moisture vapor emission over a 60 to 72 hour test.
    • In-slab relative humidity (ASTM F2170): a probe set at 40% of slab depth for slabs drying from one side, read after 24 hours of equilibration. Neither ASTM standard sets a pass mark; the coating maker does, and typical acceptance runs roughly 75 to 80% RH.

    If the numbers are high, the options are a moisture-mitigating primer system rated for the reading, or a different floor treatment. Grinding off the efflorescence alone is not a fix. Our garage floor coating guide covers system choice, and concrete waterproofing covers walls and below-grade slabs.

    Prep when efflorescence is present

    Mechanical grinding removes the deposit and the weak, salt-laden paste under it, which acid etching does not reliably do. Vacuum, then check for fresh bloom after a day or two; if it reappears quickly, moisture is still moving. Repair cracks that carry water first (see concrete crack repair), because white streaks under a crack mean the crack itself is the path.

    FAQ

    Efflorescence questions

    Is efflorescence harmful?

    Usually not to the concrete or masonry itself; the Brick Industry Association describes it as normally harmless. It is a sign of water moving through the material, though, and salts that crystallize inside the surface can cause spalling. It is also a common cause of coating and paint failures.

    Will efflorescence go away on its own?

    Often, yes. New building bloom in the first year typically fades as construction water dries out, and most soluble salts wash or weather off. If it keeps returning after the first year, there is an ongoing water source to find.

    Does vinegar remove efflorescence?

    Vinegar is a weak acid and can dissolve light calcium carbonate deposits, and it is useful as a test because carbonate fizzes. For heavier crust, TEK 08-03A refers to dilute muriatic acid at 5 to 10 percent, or 2 percent on colored units, used on a pre-wetted surface and rinsed well. Proprietary efflorescence cleaners are gentler alternatives.

    Should I pressure wash efflorescence?

    Be careful. Dry brushing is the recommended first step. Washing adds water, and BIA advises doing it only in warm, dry weather so the surface dries fast. High pressure can also open the surface and drive water deeper.

    Is efflorescence a sign of a foundation problem?

    It is a sign of moisture, not of structural failure. Efflorescence along a crack shows that water is getting through that crack. Have a professional look if you also see widening cracks, bowing walls or active leaks.

    Can I seal over efflorescence?

    Clean it off and let the surface dry first, and fix the water source if you can. Sealing over salt traps it, and non-breathable sealers on damp walls tend to blister. Breathable silane or siloxane water repellents are the usual choice for walls and pavers.

    How is efflorescence different from mold?

    Efflorescence is crystalline, usually white, and dissolves in water or fizzes with vinegar. Mold looks fuzzy, often has color, may smell musty, and smears rather than crumbles. Both need moisture, so finding the source fixes both.

    AT
    Written by the ArmorThane technical team. ArmorThane has manufactured polyurea, polyurethane and polyaspartic coatings in Springfield, Missouri since 1989, and supports a network of certified applicators. Updated October 2026.

    Sources

    1. CMHA (formerly NCMA), TEK 08-03A Control and removal of efflorescence: cmha.org TEK 08-03A
    2. Brick Industry Association, Technical Note 23A Efflorescence: causes and prevention: gobrick.com/media/file/23a-tn23a.pdf
    3. HASA, Muriatic acid safety data sheet: hasa.com/.../Muriatic Acid - Safety Data Sheet.pdf
    4. Tnemec, 3 ways to test concrete moisture (ASTM D4263): tnemec.com/remedy-index-page/3-ways-test-concrete-moisture
    5. IFTI, ASTM F2170 vs F1869 moisture testing: ifti.com/concrete-moisture-testing-astm-f2170-vs-f1869-guide

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