Efflorescence on Chicago Brick: What the White Stain Is Telling You

By Affordable Tuckpointing Pros, a Chicago tuckpointing and brick repair company in business since 1996. License number MC6337.

Direct answer

Efflorescence is the white, powdery crystalline deposit left on brick when water carrying dissolved salts reaches the surface and evaporates. [1] The salts are usually not from the brick. BIA says they most commonly originate in the materials touching the brick, such as mortar, grout, concrete masonry, concrete or soil. [1] It is normally harmless to the masonry itself. [2] What matters is the timing: on brickwork less than a year old it is new building bloom, a normal consequence of construction water drying out. [1] When it shows up more than a year after construction, BIA attributes it to excessive water penetration or poor drainage, and it is often most severe in winter or periods of cold weather. [1] On an established building that was previously clean, BIA says the appearance of efflorescence is usually attributable to a new source of water in the masonry. [1] That is the useful signal. The stain is a moisture gauge, and the correct first move is to find the leak, not to scrub the wall.

TL;DR

• Efflorescence needs three things at once: soluble salts, water in contact with them long enough to dissolve them, and a pore structure plus a driving force to carry the solution to a surface where it can evaporate. [1] Remove any one and it stops. [1]
• The brick usually is not the culprit. It is just the visible surface. Salts more commonly migrate from mortar, grout, concrete backing, trim or soil. [1]
• Not every white mark is efflorescence. Lime run and white scum are routinely mistaken for it, and both are water insoluble, so the treatment is completely different. [2]
• Under a year old, uniform across the wall: new building bloom, and BIA says to allow a year of weathering to remove it naturally. [1] [4]
• Over a year old, or newly appeared on a clean building: treat it as a water-entry problem. [1] BIA’s maintenance guidance is to scrutinise masonry with persistent efflorescence for unresolved water penetration. [3]
• Fix the water first. BIA is explicit that water ingress should be investigated and resolved before cleaning, otherwise the efflorescence will return. [3]
• Do not reach for acid. Improper cleaning can leave white scum, manganese or vanadium stains that are not water soluble and are harder to remove than what you started with. [4] [2]
• A coating is not the fix. Salts stopped behind a coating crystallise inside the brick and BIA says that can develop tremendous pressures and result in spalling. [1] NPS says coatings can be especially damaging on masonry that contains salts. [5]

One liner: efflorescence is not a stain problem, it is a plumbing problem wearing a stain costume.

What is efflorescence, and what is actually happening inside the wall?

In short: Water dissolves salts somewhere inside the wall, carries them to a surface, evaporates, and leaves the salt behind as a white crystalline crust.

BIA states the mechanism plainly: efflorescence occurs when water containing dissolved salts is brought to the surface of masonry, the water evaporates and the salts are left on the surface. [1] The salt solution can travel across the surfaces of the units, between the mortar and the brick, or straight through the pores of the mortar or the brick. [1]

Three conditions have to be true simultaneously, and BIA lists them as a set. [1] First, soluble salts must be present within or in contact with the brickwork, which can mean the mortar ingredients, the backing materials, the trim, the adjacent soil or the brick itself. [1] Second, a source of water must be in contact with those salts for long enough to dissolve them. [1] Third, there must be a pore structure that allows the salt solution to migrate to the surface, plus a driving force such as a temperature or humidity gradient to push the moisture through that pore structure. [1]

That third condition is the one homeowners tend to skip past, and it is the one that explains the seasonality. The wall is not just wet; something is driving moisture through it in a particular direction. When the inside of a Chicago house is warm and dry and the outside is cold, the gradient runs outward through the wall, and the face of the brick becomes the place where evaporation happens.

The practical consequence of the three-condition rule is that you have three places to intervene, and BIA says eliminating either the salts or the moisture will suffice to prevent or minimise it. [1] In practice the salts are effectively impossible to remove from an existing wall. BIA notes it is not practical to attempt to exclude all soluble salts from masonry materials, nor is it possible to prevent moisture from coming into contact with masonry exposed to the weather, but that reducing each contributing factor is a realistic approach. [1] So on a standing building, the water is the lever you actually have. BIA says the most effective means of preventing efflorescence is to minimise the amount of water that penetrates brickwork. [1]

Is the white stain on your brick actually efflorescence?

In short: Probably, but not certainly. Lime run and white scum look similar and are water insoluble, and misidentifying them leads to the wrong cleaning method.

This is the step most people skip, and BIA devotes a whole Technical Note to it. Not all white stains on brick masonry are necessarily efflorescence; lime run and white scum are other types of white stain that are occasionally mistaken for it. [2] BIA warns that misidentification of a stain may result in application of an inappropriate cleaning method, which may result in further staining or damage to the brickwork. [2]

There is a simple field test built into the chemistry, and it is the single most useful thing in this article. Efflorescence is water soluble. [2] [3] Lime run, after it fully carbonates, is not. [2] White scum is not water soluble like efflorescence and cannot be removed as easily. [2] So wet a small patch with plain water and watch. If the white disappears while wet and returns as it dries, you are almost certainly looking at efflorescence. If it sits there unchanged under water, you are looking at something else and the cleaning method has to change with it.

Lime run. BIA describes calcium carbonate deposits, sometimes called lime run, as white or grey crusty formations, and says these are not technically a stain but a deposit. [2] It typically emanates from weep holes or from fine cracks between brick and mortar joints. [2] The name refers to the pattern the salt makes as it travels down the face of the wall. [2] The mechanism is like a stalactite: lime run forms where a large quantity of water dissolves water-soluble calcium compounds, and it tends to follow the same path over an extended period of time, so the dissolved calcium reaches the surface, reacts with carbon dioxide in the atmosphere and forms a hard, crusty calcium carbonate deposit. [2] Because calcium carbonate is not water soluble, it will not wash away with rainwater and may be more difficult to remove. [2] Critically, BIA says once lime run begins it is likely to continue until the water source is stopped. [2] A crusty white streak running out of a weep hole or a single joint is therefore a much louder alarm than a general haze: it means a specific, sustained flow of water is running through a specific path in your wall.

One aside worth correcting, because the name misleads people into blaming the wrong ingredient. BIA says the term lime run can be misleading since the stain is not a direct result of the lime component in the mortar, and that hydrated lime can actually help reduce the risk of lime run. [2] The calcium comes from cementitious materials in the trim, mortar, backing or other construction materials. [2]

White scum. Silicate deposits, often called white scum, usually appear as white or grey discolorations on the face of the brickwork, either over the whole face or in smaller, irregularly shaped areas. [2] This one is self-inflicted. BIA says white scum is typically related to cleaning brickwork with unbuffered hydrofluoric or hydrochloric (muriatic) acid or other improper acidic cleaners, and that it can also occur when an insufficient amount of water is used while prewetting or rinsing during cleaning. [2] Components of the brick and mortar dissolve in the acidic cleaner and produce insoluble silicate deposits on the wall surface. [2] If your brick looked fine until somebody cleaned it and now carries a permanent white haze, this is the likely explanation, and it needs specialty cleaning solutions rather than water. [2]

Coloured relatives. Two other deposits work by the same migration mechanism but are not white, and they are worth recognising because they also point at acid misuse. Vanadium stains are yellow, green or purple deposits that occur when vanadium salts in the clays used for light-coloured brick meet an acidic environment such as unbuffered acid cleaners or acid rain. [2] Manganese staining produces tan, brown or occasionally grey staining on mortar joints, from manganese used as a colouring agent in tan, brown, black or grey brick reacting to acid. [2] BIA is blunt that unbuffered hydrofluoric or hydrochloric (muriatic) acid must not be used to clean tan, brown, black or grey brick. [2]

When to stop guessing. BIA recommends that when you are uncertain of the composition or origin of efflorescence or a stain, experienced brick personnel or professionals verify it before cleaning, and that in some cases samples need laboratory testing. [2] For a salt you genuinely cannot identify, BIA lists the laboratory options: X-ray diffraction, petrographic analysis, ion chromatography or chemical analysis to determine the types and amounts of salts present, results which also help determine an appropriate cleaning solution. [1]

If the brick is not to blame, where are the salts coming from?

In short: Mostly from whatever is touching the brick. Mortar and concrete backing carry far more soluble salt than fired clay does.

BIA addresses the assumption head on: individuals who have not previously observed efflorescence generally assume it is caused by the material on which it appears, usually the brick. [1] In fact the soluble compounds contributing to efflorescence on the surface of brick are most commonly found to have originated from the materials in contact with the brick, such as mortar, grout, concrete masonry, concrete, soil or other materials, although they can also originate within brick units. [1] The reason the brick takes the blame is simply that it is darker and more visible, and it is capillary porous, which BIA notes is necessary for the bond between brick and mortar in the first place. [1]

Mortar and grout. BIA calls mortar a significant contributor and quotes research describing it as the primary and most obvious source of contamination of otherwise efflorescence-free brick, because the mortar is in intimate contact with the brick on at least four and sometimes five sides and is applied wet, which provides ample moisture to transfer soluble salts into the brick. [1] Within the mortar, the principal contributor is the alkali content of the portland cement, and cements high in alkalies are more prone to produce efflorescence than cements of lower alkali content. [1] There is a spec-level control for this: ASTM C150 includes provisions for specifying low-alkali cement, limiting equivalent alkalis to a maximum of 0.60 percent. [1] BIA also notes that efflorescence can be more prominent when the mortar is not tempered with enough water, because poor hydration of the cement makes the alkali salts more mobile. [1] Lime, by contrast, has been demonstrated not to contribute generally, and BIA says lime, clay or sand additions tend to dilute the deleterious effects of high-alkali cement while improving bond and thereby increasing the water resistance of the masonry. [1]

Backing materials. This is the number that reframes the problem. BIA reports that measurements of soluble salt contents have shown concrete products can contain two to seven times as much soluble material as fired clay. [1] If your brick veneer is in direct contact with a concrete block backing, or if mortar droppings bridge the cavity, you have connected the brick to a much richer salt reservoir than the brick itself. [1] This is why BIA recommends drainage walls with a clear air space for maximum resistance to rain penetration and minimum efflorescence: the cavity lets water drain down the back of the veneer and out without wetting other materials, and it prevents salt migration from the backing by physically isolating the veneer from it. [1] For the same reason, BIA does not recommend the barrier-wall approach of filling the collar joint between wythes with mortar or grout, because that places a source of salts in direct contact with the brickwork. [1]

Trim, sills and copings. Caps, copings, sills, lintels and keystones may be natural stone, cast stone or precast concrete, any of which may contain soluble salts, and BIA notes these elements are frequently used in exactly the locations most vulnerable to water penetration, so all three conditions for efflorescence are met almost anywhere trim is used. [1] On a Chicago two-flat or greystone, the limestone sills and the coping course at the parapet are prime suspects for both the salt and the water. BIA’s mitigations are slope on the top surface to shed water, trim that needs fewer joints than a traditional rowlock sill, and flashing placed to act as a capillary break between the trim and the brickwork. [1]

The ground. Soluble salts in soil dissolve into percolating water, so most groundwater carries a high concentration of them, and where masonry is in direct contact with earth, groundwater may be absorbed and rise through capillary action several feet above the ground. [1] If your efflorescence is a band along the bottom few courses of the wall or across a foundation, that is the pattern to suspect. BIA’s remedy is a waterproof membrane on the earth side of the masonry extending below grade, plus flashing installed within 10 inches of grade to act as a capillary break that prevents absorbed salts rising higher in the wall. [1] That is a masonry waterproofing scope, not a cleaning scope.

Condensation. Water does not have to come from outside. BIA notes that air movement within walls and differences in humidity between inside and outside air can move water vapour to places where it condenses, and that on occasion accumulation of condensed water within a wall provides enough moisture to cause brickwork to effloresce. [1] It typically contributes when moisture originating inside the building travels out toward the brickwork, and BIA specifically flags cold weather: during cold weather, building interiors conditioned to normal comfort settings may contain enough moisture to cause condensation at lower temperatures. [1] Indoor sources like cooking, bathing and washing raise the risk. [1]

Acid cleaning. Worth noting because it is a loop. BIA’s table of common efflorescence sources attributes potassium chloride and vanadyl chloride to acid cleaning. [1] Cleaning a wall badly can create the next round of deposits.

Is efflorescence damaging your brick, or just embarrassing it?

In short: The surface deposit itself is normally harmless. The danger is the version you cannot see, where salt crystallises inside the brick instead of on it.

Take the pressure off first: BIA says that although undesirable, efflorescence is usually not harmful to brick masonry, and describes it as normally harmless. [1] [2] A white haze on your wall is not an emergency and it is not structural damage.

The qualifier matters, though. BIA notes that under certain specific circumstances and conditions it is possible for the crystals of efflorescence to form within the bodies of brick units, and when this occurs the growth of crystals and the resulting pressure may cause cracking and distress to masonry. [1] NPS describes the same phenomenon from the conservation side: excessive moisture may carry waterborne soluble salts through the walls, and if the water is permitted to come to the surface the salts appear as efflorescence upon evaporation, but the salts can be potentially dangerous if they remain in the masonry and crystallise beneath the surface as subflorescence, which eventually may cause the surface of the masonry to spall. [5]

Read those two together and the logic is almost reassuring. Salt arriving on the outside of your brick is salt that is not crystallising inside it. The visible deposit means the wall is still able to dry outward. The failure mode is what happens when you interfere with that drying, which is the subject of the section on coatings below, and it is the mechanism behind a lot of the spalled brick faces you see on older Chicago buildings.

There is also a slower, more expensive kind of damage that has nothing to do with the salt itself. The water carrying the salt is the same water that sits in mortar joints, wets the back of the veneer and reaches embedded metal. BIA’s maintenance guidance lists efflorescence alongside spalling, deteriorating mortar joints, interior moisture damage and mould growth as conditions that may necessitate maintenance or repair, and says that once one of these becomes evident the origin of the problem should be determined and action taken to correct both the cause and the visible effect. [3] Both halves of that sentence matter. Correcting only the visible effect is washing the wall.

Why does it keep coming back every winter?

In short: Because winter is when the wall is wettest and the drying gradient runs hardest outward. BIA says post-year-one efflorescence is often most severe in cold weather.

BIA draws a hard line at the one-year mark, and it is the most useful diagnostic in the whole subject.

Efflorescence appearing on newly constructed brickwork less than a year old is called new building bloom. [1] It generally appears in a fairly uniform pattern across the wall surface and is attributed to normal evaporation of water after construction is complete. [1] BIA describes this as the simplest and most common mechanism: migration of free-alkali solutions from the mortar into the brick. [1] In most cases it dissipates over time if the brickwork is allowed to dry and if wind and rain are given sufficient time to clean the brickwork naturally. [1] BIA’s cleaning guidance says to allow one year of weathering to naturally remove new building bloom. [4] If your masonry was laid last season and the bloom is even across the elevation, the correct action is genuinely to do nothing.

After that first year the meaning changes completely. BIA says that when efflorescence occurs more than a year after construction is complete, it can generally be attributed to excessive water penetration or poor drainage, and is often most severe in winter or periods of cold weather. [1] Efflorescence that reappears after the initial post-construction period is likely due to water entering and remaining in the wall. [1]

So a Chicago wall that blooms white every February is telling you something specific. It is not a seasonal cosmetic quirk to be washed off each spring. The cold-weather severity is consistent with the mechanism: more water in the wall from autumn rain and snow, less evaporation while it is cold, and a strong outward temperature and humidity gradient once the heat is on inside, which is precisely the driving force BIA names as the third necessary condition. [1] Condensation of interior moisture adds to it, and BIA specifically notes that during cold weather, interiors at normal comfort settings may hold enough moisture to condense at lower temperatures. [1]

The sharpest version of the signal is the one BIA gives for buildings that were previously clean: the appearance of efflorescence on an established building that had previously been free of efflorescence is usually attributable to a new source of water in the masonry. [1] New stain on an old wall means something changed. A coping cracked, a sealant joint failed, a downspout came loose, a gutter blocked, a flashing lap opened. Something is admitting water this year that was not admitting it last year, and the salt is drawing you a map to it.

What is the stain telling you about where water is getting in?

In short: Location is evidence. BIA gives a seven-point troubleshooting sequence and an inspection checklist that together turn a stain into a work list.

BIA publishes an explicit troubleshooting procedure for determining the cause and extent of an efflorescence problem, and it is worth walking in order rather than jumping to the pressure washer. [1] Condensed, it runs like this.

1. Date it. Determine the age of the structure when the efflorescence first appeared. [1] Under a year and the source of the salts is often the cement in the mortar and the source of moisture is construction water. [1] Over a year and construction details should be examined to identify possible leaks in the wall or in the surrounding construction. [1]

2. Map it. Observe the location of the efflorescence, both on the structure and on the individual units or mortar joints, because the location on the building may offer information about where the water is entering. [1] BIA also asks what has changed in the recent use or occupancy of the building, such as whether it has been vacant or whether there has been new construction. [1] Note whether the deposit is only on the mortar joints, confined to limited areas, or covering the whole surface, since BIA describes all three patterns. [2]

3. Examine the masonry. BIA’s list here is effectively the inspection: the profile of the mortar joints, the condition of the mortar, the quality of workmanship, the condition of caulking and sealant joints, the condition of flashing and drips, obstructed weeps, and any deterioration or eroding of mortar joints in copings or in sills. [1] These should offer clues as to the entry paths of moisture. [1]

4. Read the details. Review wall sections and construction details for possible paths of moisture ingress and possible sources of salt contamination, with careful examination of roof and wall juncture and flashing details. [1]

5. Check the paperwork. Review laboratory test reports on the materials of construction if available. [1]

6. Identify the salt. Knowing the composition of the efflorescing salts is useful for determining proper removal methods, and BIA tabulates the most probable source for each. [1] Calcium sulfate points at the brick; sodium and potassium sulfates at cement-brick reactions; calcium carbonate at mortar or concrete backing; sodium and potassium carbonates at mortar; calcium hydroxide at cement; potassium chloride and vanadyl chloride at acid cleaning; sodium chloride at seawater. [1]

7. Consider the unglamorous sources. When the obvious sources are eliminated, BIA says to consider condensation within the wall, poorly directed landscape sprinklers, leaky pipes, faulty drains, and condensation on heating or plumbing pipes. [1]

Alongside that, BIA’s maintenance note gives an inspection checklist organised by location, and it is a good structure for walking your own building. Above grade, on masonry, it lists cracked units, loose units, spalled units, hairline cracks in mortar, deteriorated mortar joints, missing or clogged weeps, plant growth, deteriorated or torn sealants, out-of-plumb, efflorescence, stains and water penetration. [3] For flashing and counterflashing it lists damaged, open lap joints, missing and stains. [3] For caps, copings and sills it lists inadequate slope, cracked units, hairline cracks in mortar, loose units, open joints, out-of-plumb and drips needed. [3] Below grade it covers foundation walls and retaining walls for deteriorated mortar joints, cracks, dampness, inadequate drainage and water penetration, and it separately lists roof overhangs, gutters and leaders, seals at adjacent materials, and grade and drainage. [3]

Two practical notes from the same source. BIA recommends exterior surveys be performed with binoculars to permit close-range observation of conditions on upper floors, and suggests using adjacent balconies or roof areas to see parts of the facade that are hard to see from the ground. [3] It also recommends seasonal inspection periods so the behaviour of building materials in various weather conditions can be observed, and says interior surveys should note stains or damage to finishes that may indicate potential water ingress. [3] For a wall that only blooms in winter, inspecting it in July tells you very little.

Finally, know when the problem has stopped being maintenance. BIA lists observed conditions that are structural rather than maintenance items, including cracks in brick masonry exceeding 0.075 inches (2 mm) in width, cracks through multiple brick units, cracks following a stepped or diagonal pattern, widespread spalled brick, accumulated rust on lintels or shelf angles, out-of-plane movement, and neutral or negative slope on masonry sills and water tables. [3] It says such issues generally warrant investigation by a professional engineer. [3] If your efflorescence comes with any of those, the salt is the least interesting thing on the wall.

How do you remove efflorescence without making it worse?

In short: Fix the water, let the wall dry, then use the gentlest thing that works. Dry brushing first, water second, proprietary cleaner third, acid essentially never.

The sequence is not a stylistic preference. BIA states that prior to cleaning efflorescence, potential water ingress issues in the area should be investigated and resolved, otherwise the efflorescence will return; any leaks should be repaired and the brickwork allowed to dry. [3] The cleaning note repeats it: before efflorescence is removed, any sources of moisture ingress should be repaired and the brickwork allowed to dry. [4] Cleaning first is how people end up washing the same wall every spring for a decade.

Start with nothing. Most efflorescing salts are water soluble and many will disappear of their own accord with normal weathering, which BIA says is especially true of new building bloom. [1] [4] Allow one year of weathering for new building bloom. [4]

Then dry brushing. Where weathering has not done it, efflorescence usually can be removed by dry brushing. [1] BIA describes removing light efflorescence by dry-brushing or brushing with a stiff fibre brush and water. [4] Use a fibre brush, not a wire one.

Then a proprietary cleaner, carefully. Heavy accumulations or stubborn deposits may be removed with a proprietary cleaner formulated specifically for brickwork, following the manufacturer’s instructions, and BIA says it is important to test all cleaning solutions on a small area prior to full-scale application. [1] [4] BIA’s maintenance guidance adds that improper cleaning procedures such as insufficient prewetting, insufficient rinsing and strong chemical concentrations may cause additional staining, etched mortar joints and increased moisture penetration in brickwork, and warns that stains caused by improper cleaning are not water soluble. [3] That is the trap: you can convert an easy, water-soluble problem into a permanent one in an afternoon.

Do not wash it in the cold, and do not wash it wet. BIA says it is usually not advisable to wash efflorescence off brickwork except in warm, dry weather, since washing results in considerably more moisture, which may bring more salts to the surface. [1] The cleaning note puts numbers on the weather window. Chemical cleaning solutions are generally more effective when the outdoor temperature is 50 °F (10 °C) or above. [4] Do not clean during freezing weather or when freezing weather is expected, in order to avoid harming the masonry or increasing the risk of efflorescence. [4] Water-only methods are preferred when the ambient temperature will be 40 °F or above and will remain so until the wall is dry, and ideally temperatures should be above freezing for seven days after cleaning is completed. [4] In Chicago that rules out a large part of the year, and it rules out exactly the months when the stain is worst. Note the wall.

Things not to do. BIA says cleaning failures generally follow from a short list. Failure to thoroughly saturate the brick surface with water before and after applying chemical or detergent cleaning solutions, because dry masonry absorbs the cleaning solution and may result in white scum, efflorescence, manganese or vanadium stains. [4] Use of improper chemical cleaning solutions, where improperly mixed or overly concentrated acid can etch the brick or dissolve cementitious material from the joints, and unbuffered acid tends to discolour masonry units, particularly lighter shades, producing acid burn. [4] Excessively aggressive methods such as abrasive blasting and high-pressure water cleaning, which remove stains by abrasion and can etch mortar joints and remove the outer surface of the brick, resulting in permanent damage. [4] And failure to protect windows, doors and trim, since many cleaning agents, particularly acid solutions, are corrosive to metal. [4]

One detail people never think about: the water itself. BIA says water used for cleaning should be potable and that iron content should be less than 2 parts per million by weight, and to check whether local water includes additives or softeners that may cause issues. [4]

NPS adds a caution that applies to any wash of a salt-bearing wall, historic or not: cleaning may draw the salts to the surface, where they will appear as efflorescence, which may require a second treatment to be removed. [5] Expect a rebound bloom after washing and do not panic at it. NPS also warns that testing the cleaner on an inconspicuous spot is always necessary, and notes that hydrofluoric acid can etch masonry, leaving a hazy residue of whitish deposits of silica or calcium fluoride salts. [5] That is the same white scum failure BIA describes, from the other direction. [2]

And if the joints themselves are gone, cleaning is the wrong trade entirely. Open and eroded joints are a water entry path, and closing them is tuckpointing work, not cleaning work. BIA’s own service-life table puts mortar in walls at 50 or more years, so joints that have failed early are usually telling you about water too. [3]

Will sealing the brick stop the efflorescence?

In short: No, and it can convert a harmless surface deposit into spalling. The salt does not leave; it just crystallises where you cannot see it.

Clear water repellents, silicone and acrylic coatings are among the solutions often suggested for preventing efflorescence, and BIA addresses the idea directly. [1] A coating may prevent efflorescence from recurring by reducing the amount of water an exposed masonry surface absorbs. [1] But applying a coating to brickwork that has a tendency to effloresce, without stopping the mechanisms causing that efflorescence, may lead to degradation of the masonry, and applying a coating that inhibits evaporation of water from the masonry may also lead to degradation. [1]

The mechanism is worth understanding, because it is the reason this is not simply a judgement call. As water and dissolved salts travel toward a coated exterior surface, they may be stopped at the inner margin of the coating, usually an eighth to a quarter of an inch (3 to 6 mm) below the surface. [1] At that point the water evaporates and passes through the treated zone as vapour, but the salts are deposited inside the masonry. [1] BIA calls this cryptoflorescence or subflorescence, and says salts crystallising within masonry can develop tremendous pressures which may result in brick spalling. [1] Its conclusion is unambiguous: coatings are not recommended as the sole treatment for efflorescence problems. [1]

NPS reaches the same place. Subflorescence eventually may cause the surface of the masonry to spall, particularly if a water-repellent coating has been applied which tends to reduce the flow of moisture out from the subsurface of the masonry. [5] And although many newer water-repellent products are more breathable than their predecessors, NPS says they can be especially damaging if applied to masonry that contains salts, because they limit the flow of moisture through masonry. [5] A wall showing efflorescence is, by definition, masonry that contains salts. NPS also says a water-repellent coating should never be applied to a damp wall, and that if masonry buildings are kept watertight and in good repair, water-repellent coatings should not be necessary. [5]

So the wall that looks most like it needs sealing is the wall where sealing is most likely to do harm. We have written separately on what a brick sealer does and does not fix; for efflorescence specifically, the answer is that it treats the symptom by hiding the evidence and moves the crystallisation somewhere more expensive.

Efflorescence questions Chicago homeowners ask

What causes efflorescence on brick?

Water dissolving soluble salts inside or in contact with the brickwork, carrying them to the surface and evaporating there. [1] BIA says three conditions must exist at once: soluble salts present, water in contact with them long enough to dissolve them, and a pore structure plus a driving force such as a temperature or humidity gradient to carry the solution to an evaporating surface. [1]

Is efflorescence on brick harmful?

The surface deposit is usually not harmful to brick masonry. [1] It is normally harmless. [2] The risk is subflorescence, where salts crystallise beneath the surface instead. BIA says crystals forming within brick units can cause cracking and distress, and NPS says subflorescence may eventually cause the surface to spall. [1] [5]

Does efflorescence mean my brick wall is leaking?

After the first year, usually yes. BIA attributes efflorescence occurring more than a year after construction to excessive water penetration or poor drainage. [1] Its maintenance guidance is to scrutinise masonry with persistent efflorescence for unresolved water penetration issues. [3] On a building that was previously clean, BIA says new efflorescence is usually attributable to a new source of water in the masonry. [1]

How do I know if the white stain is efflorescence or something else?

Test it with water. Efflorescence is water soluble. [2] [3] Lime run, once fully carbonated, is not, and white scum is not water soluble like efflorescence and cannot be removed as easily. [2] BIA recommends having experienced brick personnel or professionals verify the identification when you are uncertain, because misidentification can lead to a cleaning method that causes further staining or damage. [2]

What is new building bloom?

Efflorescence on brickwork less than a year old. [1] It generally appears in a fairly uniform pattern across the wall and is attributed to normal evaporation of construction water. [1] In most cases it dissipates if the brickwork is allowed to dry and wind and rain are given time to clean it naturally, and BIA’s cleaning guidance is to allow one year of weathering. [1] [4]

Why is my efflorescence worse in winter?

BIA says efflorescence occurring more than a year after construction is often most severe in winter or periods of cold weather. [1] Cold weather also raises the chance that interior moisture condenses within the wall, and BIA notes that during cold weather, building interiors at normal comfort settings may contain enough moisture to cause condensation at lower temperatures. [1]

Should I use muriatic acid to clean efflorescence off my brick?

No. BIA says white scum is typically related to cleaning with unbuffered hydrofluoric or hydrochloric (muriatic) acid, and that such acid must not be used on tan, brown, black or grey brick because of manganese staining. [2] Acid cleaning is also listed as the probable source of potassium chloride and vanadyl chloride efflorescence. [1] Stains caused by improper cleaning are not water soluble. [3]

Can I just pressure wash it off?

It is a poor idea. BIA lists high-pressure water cleaning and abrasive blasting among excessively aggressive methods that remove stains by abrasion and can etch mortar joints and remove the outer surface of the brick, resulting in permanent damage. [4] Washing also adds moisture, and BIA says it is usually not advisable to wash efflorescence off except in warm, dry weather because washing may bring more salts to the surface. [1]

When is it too cold to clean efflorescence in Chicago?

BIA says chemical cleaning solutions are generally more effective at 50 °F (10 °C) or above, and not to clean during freezing weather or when freezing weather is expected, to avoid harming the masonry or increasing the risk of efflorescence. [4] Water-only cleaning is preferred when ambient temperature will be 40 °F or above and stay there until the wall is dry, ideally with temperatures above freezing for seven days after cleaning. [4]

Will a sealer or water repellent stop efflorescence?

Not reliably, and it can cause damage. BIA says coatings are not recommended as the sole treatment for efflorescence problems, because salts stopped at the inner margin of the coating crystallise inside the masonry and can develop tremendous pressures that may result in brick spalling. [1] NPS says water repellents can be especially damaging on masonry containing salts because they limit moisture flow through the masonry. [5]

Does efflorescence come from the brick itself?

Usually not. BIA says the soluble compounds are most commonly found to have originated in materials in contact with the brick, such as mortar, grout, concrete masonry, concrete or soil, although they can also originate within brick units. [1] Measurements have shown concrete products can contain two to seven times as much soluble material as fired clay. [1]

There is a white crust coming out of one weep hole. What is that?

That pattern fits lime run rather than general efflorescence. BIA says calcium carbonate deposits called lime run appear as white or grey crusty formations and can be found emanating from weep holes or fine cracks between brick and mortar joints. [2] It is water insoluble once carbonated, will not wash away with rainwater, and BIA says once it begins it is likely to continue until the water source is stopped. [2]

Why does efflorescence show up along the bottom of my foundation wall?

Probably groundwater. BIA says most groundwater contains a high concentration of soluble salts, and where masonry is in direct contact with the earth, groundwater may be absorbed and rise through capillary action several feet above the ground. [1] The recommended fix is a waterproof membrane on the earth side of the masonry extending below grade plus flashing within 10 inches of grade to act as a capillary break. [1]

Do I need to fix anything before cleaning the efflorescence?

Yes. BIA says potential water ingress issues should be investigated and resolved prior to cleaning, otherwise the efflorescence will return, and that leaks should be repaired and the brickwork allowed to dry first. [3] [4]

Stats box

Definition bank

Entity cards

Efflorescence

New building bloom

Subflorescence

Lime run

White scum

Reading your wall before you scrub it

In short: the white is evidence. Photograph it, date it, note exactly where it sits, and
find the water it is pointing at before anyone quotes you to clean it.

Efflorescence is the cheapest diagnostic your building will ever give you. It is free, it is
self-installing, and it appears in the specific places where water is moving through the wall and
evaporating. BIA’s whole approach treats it that way: determine the origin of the problem and correct
both the cause and the visible effect of the condition. [3] Correcting only the visible effect is a
wash, and washes do not last.

So before you accept a cleaning quote, work the sequence. Date the first appearance, because under a
year means wait and over a year means look for a leak. [1] Map where it sits, on the units or the
joints, in a band or across the whole elevation. [1] [2] Then walk the checklist: joint profile and
mortar condition, caulking and sealant joints, flashing and drips, obstructed weeps, and eroded joints in
copings and sills. [1] Add the boring suspects, which BIA lists as condensation in the wall, misdirected
landscape sprinklers, leaky pipes, faulty drains and condensation on pipes. [1] And do it in the season
when the stain is present, since BIA recommends seasonal inspections so materials can be observed in
various weather conditions. [3]

A contractor who looks at a white wall and quotes you a cleaning has answered a question you did not
ask. One who comes back with an open coping joint, a sill with no drip, a blocked weep and a downspout
discharging against the foundation has found the thing that is actually costing you money, and the
cleaning becomes a fifteen-minute job at the end of it. If the water is coming through below grade or
through the face of the wall, that is a
masonry waterproofing scope; if it is coming through
failed joints, it is a tuckpointing scope.

If you want that read on your own building, get a free quote and we will tell
you what the stain is telling us.

Sources

1. Brick Industry Association, Technical Note 23A, “Efflorescence: Causes and Prevention”, June 2019. https://www.gobrick.com/media/file/23a-tn23a.pdf
2. Brick Industry Association, Technical Note 23, “Stains: Identification and Prevention”, June 2019. https://www.gobrick.com/media/file/23-tn23.pdf
3. Brick Industry Association, Technical Note 46, “Maintenance of Brick Masonry”, December 2017. https://www.gobrick.com/media/file/46-maintenance-of-brick-masonry.pdf
4. Brick Industry Association, Technical Note 20, “Cleaning Brickwork”, August 2018. https://www.gobrick.com/media/file/20-cleaning-brickwork.pdf
5. National Park Service, Preservation Brief 1, “Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings”, Mack and Grimmer, 2000. https://www.nps.gov/orgs/1739/upload/preservation-brief-01-cleaning-masonry.pdf