Quick answer
Foundation efflorescence is a white or light-colored deposit of soluble salts on the surface of a concrete, block or brick foundation wall, left behind when water carries the salts to the surface and evaporates. The deposit is a symptom of moisture moving through the wall, not a material of its own.
A little is common on new masonry and usually harmless. Persistent or repeated deposits point to a continuing moisture source that deserves a closer look at drainage, grading and the wall.
Quick facts
The key facts about Foundation Efflorescence, with sources:
- Three conditions
- Soluble salts, water to dissolve them, and pores or paths to the surface 2
- Common salts
- Sulfates and carbonates of sodium, potassium, calcium, magnesium and aluminum 2
- New construction
- Some appears on all masonry after construction and is not harmful 1
- Persistent or repeated
- May indicate excessive internal moisture, rising damp or other problems to investigate 1
- Not a crack diagnosis
- It shows moisture moved through; it does not show whether a wall is moving 1
Key takeaways
- Efflorescence is salt left on a wall surface after water carries it there and evaporates 12.
- It needs three things at once: soluble salts, water to dissolve them and a path to the surface 2.
- A little on new masonry is normal and is not harmful, according to a federal technical bulletin 1.
- Repeated or heavy deposits can point to excess internal moisture or rising damp 1.
- Cleaning without fixing the water usually brings it back, and coatings are not recommended as the only treatment 2.
- Efflorescence does not prove a structural problem, and it does not prove water is leaking in.
What efflorescence is
Efflorescence is the white or light-colored crust, powder or fuzzy growth you may see on a basement wall.
The National Institutes of Health technical bulletin on masonry describes it as a white or light-colored substance on the surface of concrete, brick, cast stone and other masonry, made of soluble alkaline salt deposits brought to the surface by water moving within the wall 1.
The Brick Industry Association states the process simply: water containing dissolved salts reaches the surface, the water evaporates and the salts remain 2.
The deposit is a trace, not a threat in itself; it tells you that moisture has moved through the wall and dried. On a foundation, the moisture often comes from the soil side; our page on basement moisture vs. water seepage explains how to tell moisture from liquid water entering.
White powder can be other things, so a professional should identify it; the BIA lists positively identifying efflorescence as the first recommended step 2.
General information, not a diagnosis of your house
General information, not a diagnosis of your house. A photo cannot confirm what the deposit is or where its moisture comes from.
How efflorescence forms
The BIA says three conditions must exist at the same time.
Soluble salts must be present in or in contact with the masonry, a source of water must touch the salts long enough to dissolve them, and the masonry must have a pore structure that allows salt solutions to move to a surface where the water can evaporate, driven by a temperature or humidity gradient 2.
Remove any one and it stops.
Salts are unavoidable; the BIA notes that it is not practical to exclude all soluble salts from masonry materials, and that they come from mortar, groundwater, rainwater, cleaners and other sources 2.
The most common are sulfate and carbonate compounds of sodium, potassium, calcium, magnesium and aluminum 2. Portland cement also contains soluble salts, the NIH adds 1.
On a below-grade wall, the groundwater route matters; the BIA explains that when masonry touches the earth, groundwater may be absorbed and may rise by capillary action several feet above the ground, leaving efflorescing salts on the surface 2.
A damp wall does not need a leak to do this; it only needs steady moisture.
Kinds of efflorescence and what each suggests
| Kind | What you see | What it may suggest |
|---|---|---|
| New building bloom | An even pattern on masonry less than a year old | Normal evaporation of construction water; often fades if the wall can dry 2 |
| Later efflorescence | Deposits that appear more than a year after construction | Usually excessive water penetration or poor drainage; often worst in winter 2 |
| Persistent or repeated | Returns after cleaning | Excessive internal moisture, rising damp or another problem to investigate 1 |
| Subflorescence | Salt crystals forming inside the material | Crystal growth pressure can crack or distress masonry 2 |
| Condensation-linked | Deposits where humid air meets a cool wall | Condensation inside a wall can supply enough moisture 2 |
Example: reading where the deposit sits
The deposit example below shows how the location and timing of white deposits can narrow the moisture source. It is a way to organize observations, not a diagnosis.
| What you notice | Moisture clue | First thing to check |
|---|---|---|
| A band of white powder low on the wall, a few feet up from the floor | Groundwater wicking up through the wall 2 | Drainage and grading outside; any wall coating |
| White deposits only on a wall facing a downspout | Roof water near the wall 1 | Downspout outlet, gutter and slope 1 |
| Deposits near a corner or a crack, with a damp trail | Water moving through a crack or joint | Where the water comes from; a record of storms |
| Deposits that return a few weeks after cleaning | A continuing moisture source 1 | Source of water, not the cleaning method 2 |
| Heavy deposits plus flaking surface | Possible crystal pressure inside the material 2 | A professional evaluation of the wall |
Photograph the wall and note the date and weather. A professional can test for the moisture source.
Where efflorescence appears
Efflorescence shows on concrete, block, brick, stone and cast stone. In a house, the most common spots are basement and crawl space walls, the base of block walls, around window wells, on retaining and landscape walls and on the inside face of a poured wall where moisture has moved through and dried.
The NIH says landscape and retaining walls should be waterproofed to control rising damp, which it describes as moisture absorbed from the surrounding earth 1.
It tends to show up more on porous materials such as block and mortar joints; a sealed or painted wall can trap salts and then flake; our page on concrete spalling covers surface damage that can follow repeated wetting.
What efflorescence can tell you
What it is useful for
What cleaning and coatings cannot do
Cleaning removes the deposit, not the cause. The NIH says excessive efflorescence on existing walls should be removed with gentle methods that do not damage the wall, and that washing can draw out additional salts, so repeat washing may be needed 1.
We do not give cleaning-product steps. If water keeps feeding the wall, the deposit will keep coming.
Coatings are not a cure either; the BIA recommends against using coatings as the sole treatment to control efflorescence and says to correct the causes before attempting removal 2.
A sealer on a wall that is still moving moisture can trap the salts behind it; our page on foundation dampproofing explains why coatings need drainage beside them.
Efflorescence also says little about the wall’s strength. Persistent deposits should be investigated, the NIH says, to avoid more serious damage 1, but the deposit itself is a symptom of moisture, not a measure of structure.
Efflorescence vs. mold
Efflorescence is mineral salt left by evaporating water. Mold is a living growth that needs moisture. Both can show where a wall stays damp, but they are different and a professional should identify an unknown deposit. The EPA says not to paint or caulk moldy surfaces 3.
What drives the cost
We do not print prices; the deposit itself is cheap to clean; the real costs sit in the source. Cleaning drivers are the area, the material, the access and whether repeated visits are needed.
Fixing the source brings the usual drainage drivers: gutters, grading, drains, wall treatment, excavation, restoration and permits. Investigation adds cost where moisture testing or an engineer’s evaluation is needed; our cost guide shows how quotes are built, and the cost calculator helps frame scope.
What to do when you see white powder
A general sequence that stays within safe homeowner tasks.
- Look, do not scrub: Photograph the wall, date the image and note where the deposit sits.
- Identify it: Treat an unknown white deposit as unidentified until a professional confirms it 2.
- Find the water: Check gutters, downspouts, grading and plumbing near the wall 1.
- Fix the source first: The BIA says to correct the causes before attempting removal 2.
- Clean gently if needed: The NIH describes gentle washing with water or a mild detergent, and says abrasive methods are not recommended 1.
- Watch for a return: A deposit that returns points to a continuing source 1.
Keeping efflorescence from returning
Most of the work is on the water side.
- Keep gutters clean and soil sloped away from the foundation; the NIH names regrading and maintenance of drains and gutters as simple fixes 13.
- Carry downspouts well beyond the wall; Colorado’s survey uses at least 10 feet on swelling soils 5.
- Keep irrigation off the foundation edge.
- Keep humidity moderate; the EPA gives below 60 percent, ideally 30 to 50 percent 3.
- Do not sandblast or use wire brushes on masonry; the NIH says abrasive methods are not recommended 1.
- Log any return, with dates and weather.
Risks and when to call a structural engineer
The direct risk of efflorescence is small; the risk is what it points to. The BIA notes that crystals can form inside material, and that the pressure may crack or distress masonry 2. Steady moisture can also bring mold, finish damage and wear.
White powder with a crack or lean is a clue, not a diagnosis. Movement history, displacement, water, construction details and soil all change what it means.
Call a licensed structural engineer if movement is significant, widening or changing; if walls bow or are displaced; if doors and windows stick while new cracks appear; if corners separate; or if you doubt safety. Our engineer guide explains who to call.
Chemical cleaners and digging
Acidic cleaners can harm masonry and skin, and the BIA notes that improper hydrochloric acid cleaning can add chlorides 2. We do not give mixing or application steps. Do not dig beside a foundation to chase moisture; that can undermine the wall.
Rules and standards that touch it
No residential code regulates efflorescence as such. Codes address the moisture behind it. In the 2025 California Residential Code, which carries the IRC text with state edits, R405 asks for foundation drainage and R406 for dampproofing, or waterproofing where a high water table or severe soil-water conditions are known 4.
Material standards address the salts; the NIH bulletin names ASTM C150 for specifying low-alkali Portland cement and ASTM C1400 as a guide for reducing efflorescence in new masonry walls 1; those are for builders and specifiers, not homeowners. Editions and local amendments vary, so ask your building department what applies.
Edition and adoption
Code text is from the 2025 California Residential Code as shown by a code-reference site, retrieved 2026-10-14. Other places adopt other editions.
Efflorescence compared with similar signs
| Sign | What it is | How it differs |
|---|---|---|
| Efflorescence | Soluble salt left on a surface 1 | This page |
| Spalling | Surface flaking or breaking off | Physical damage that can follow repeated wetting; see spalling |
| Mold | A living growth that needs moisture 3 | Different material; the EPA says fix the water and do not paint over it 3 |
| Seepage | Water passing through a wall | Liquid water, not just salt; see basement water intrusion |
| Rising damp | Moisture absorbed from the earth 1 | A common cause; can leave deposits as it dries |
Efflorescence myths
- Myth It always means the wall is leaking.
- Reality It means moisture moved through and dried; liquid water need not be visible 1.
- Myth It is always harmless.
- Reality Some is normal on new walls, but persistent or heavy deposits should be investigated 1.
- Myth Brick or block causes it by itself.
- Reality The BIA says the assumption that the masonry unit is the cause is often wrong; salts also come from mortar, soil and water 2.
- Myth A sealer cures it.
- Reality The BIA does not recommend coatings as the sole treatment 2.
- Myth Scrubbing it off solves the problem.
- Reality Washing can draw out more salts, and the cause remains 1.
Regional factors
Where soils carry more salts or groundwater stays high, deposits are likelier. The BIA says most groundwater carries dissolved salts, and masonry in contact with the earth can absorb them 2.
Freezing climates make it worse; the BIA notes that later efflorescence is often most severe in winter or cold weather 2. Water-table depth varies by place and season 6. A local professional can read your soil and drainage. Ask your building department what applies.
What to do with this
Treat white powder as a prompt to look at water, not as a stain to remove. The water intrusion tool helps you sort sources, and the basement waterproofing guide explains how professionals trace and manage moisture.
- If A little white powder on a wall under a year old
- Then Likely new building bloom; let the wall dry and watch 2
- If Powder that returns after cleaning
- Then Find the moisture source before any more cleaning 1
- If Powder plus flaking, a crack or damp trail
- Then Ask a professional to evaluate the wall and the moisture path
- If Powder plus bowing, widening cracks or sticking doors
- Then Call a licensed structural engineer
Questions about Foundation Efflorescence
What is efflorescence on a foundation wall?
It is a white or light-colored deposit of soluble salts left on concrete, block or brick when water carries the salts to the surface and evaporates 12. It shows that moisture has moved through the wall.
Is efflorescence harmful?
Some is normal on new masonry and is not harmful, according to a federal technical bulletin. Persistent, repeated or excessive deposits may indicate excessive internal moisture, rising damp or other problems that should be investigated 1.
Does efflorescence mean my basement is leaking?
Not necessarily. It means moisture moved through the wall and dried, which can happen without visible liquid water. Steady moisture is enough. A log of storms and dates helps a professional trace the source.
What causes efflorescence?
Three things together: soluble salts in or near the wall, water that dissolves them, and pores or paths that carry the solution to a surface where it evaporates 2. On foundations, groundwater and rain are common water sources.
How do I remove efflorescence?
Fix the water source first, then clean gently. The NIH describes washing with water or a mild detergent and says abrasive methods are not recommended and repeat washing may be needed 12. We do not give chemical cleaning instructions.
Why does efflorescence keep coming back?
Because the moisture is still moving through the wall. Washing can also draw out additional salts 1. A returning deposit points to a continuing source such as poor drainage, a leak or rising damp.
Will sealing the wall stop efflorescence?
Not by itself. The BIA does not recommend coatings as the sole treatment, and says to correct the causes first 2. A sealer over a wall that keeps moving moisture can trap salts behind it.
Is white powder on my wall mold?
It could be salt or something else. Efflorescence is mineral salt, while mold is a living growth. A professional should identify an unknown deposit 2. The EPA says not to paint or caulk moldy surfaces 3.
Does efflorescence mean the foundation is damaged?
Not by itself. It marks moisture, not structure. Crystals forming inside material can crack or distress masonry in some cases 2. A licensed structural engineer should assess widening cracks, bowing or other movement.
Can drainage fix efflorescence?
Often it helps, since water is the driver. The NIH names regrading and maintenance of drains and gutters as simple corrections, while some cases need more invasive work 1. No single fix solves every moisture problem.
Sources
- NIH Division of Technical Resources, Technical Bulletin Issue 71, Efflorescence in Masonry Walls (Dec. 2017), retrieved .
- Brick Industry Association, Technical Note 23A, Efflorescence: Causes and Prevention (2019), retrieved .
- U.S. EPA, A Brief Guide to Mold, Moisture, and Your Home, retrieved .
- 2025 California Residential Code, Chapter 4, R405 and R406 (model IRC text with state edits), as shown by CodeBook, retrieved .
- Colorado Geological Survey, Special Publication 11, Home Construction on Shrinking and Swelling Soils (Holtz and Hart, 1978), retrieved .
- U.S. Geological Survey, Circular 1139, Ground Water and Surface Water (Box A, the water table), retrieved .
Expert review
Written by the HyreFoundation Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Facts were checked against an NIH technical bulletin, Brick Industry Association Technical Note 23A, EPA, the 2025 California Residential Code as quoted by CodeBook, the Colorado Geological Survey and USGS, retrieved 2026-10-14.
The BIA note concerns brick masonry; its mechanism applies to concrete and block by analogy and is stated that way. No structural engineer has reviewed this page.
Suggest a correction. We fix errors and say what changed.