The white, powdery bloom on brick and block is efflorescence — mineral salts carried to the surface by water moving through the masonry. It is a stain removal job with a twist: the deposit is the symptom, and the water that delivered it is the actual story.
What it is and where it comes from
Masonry and mortar contain soluble salts. When water enters the wall — rain, ground moisture, a leak — it dissolves them, migrates to the surface, evaporates, and leaves the salts behind as the white crust. The bloom literally maps where water travels through your wall.
New construction often blooms harmlessly in its first year or two as construction moisture leaves. Recurring bloom on established masonry is different: water is getting in from somewhere, repeatedly.
Three things have to happen at once for a bloom to appear: soluble salts in the wall, water to dissolve them, and a route to a surface where that water can evaporate. Remove any one and the bloom stops. That is why the same wall can be spotless for years and then bloom heavily after one bad winter — nothing changed about the brick, only about the water.
Evaporation rate decides where the salts end up. When the face dries slowly, the salt solution reaches the surface and deposits there as the visible powder, which is a nuisance and nothing worse. When the face dries fast — wind, sun, a sealed or painted surface that will not let vapour through — the water evaporates just inside the masonry instead, and the salts crystallise within the pores. That version is the one to worry about, because crystals growing inside a pore push outwards and can flake the face off the brick over several seasons.
Efflorescence, lime run and calcite deposits
Not every white mark on masonry is efflorescence, and the difference decides the method. Efflorescence proper is a loose, powdery, crystalline deposit sitting on the surface. It is water-soluble, which gives you a free test: wet a patch and it will largely vanish as the salts redissolve, then reappear as the wall dries.
Lime run — sometimes called calcite deposit or secondary leaching — is a different animal. Water passing through fresh mortar or a concrete element above dissolves calcium hydroxide, carries it to the face, and it reacts with air to form calcium carbonate: a hard, glassy white crust that often runs in streaks or drips below a joint, a coping or a slab edge. It does not disappear when wetted, it cannot be brushed off, and it needs stronger, more carefully controlled chemistry than a salt bloom does. Mistaking one for the other wastes a visit — scrubbing lime run with a salt-bloom method achieves very little.
The quick field version: powdery and it moves when you brush it, efflorescence. Hard, glossy, drip-shaped and it ignores water, lime run. Either way it is telling you water is passing through the wall.
Removing it properly
Dry brushing takes off loose deposit. Bonded efflorescence needs a mild acidic wash — appropriately diluted and thoroughly rinsed, because acid on masonry is a controlled tool, not a splash-on product. Pressure alone tends to drive dissolved salts back into the face to reappear as it dries.
Sequence matters as much as product. The wall is brushed dry first, so you are not turning powder into paste. It is then wetted before anything acidic touches it, so the pores are already full and the acid stays on the surface rather than being drawn into the brick. The wash is applied, given a short controlled dwell, and rinsed thoroughly from the bottom up and top down before it can dry on the face — acid left to dry is what etches brick and burns pale patches into mortar.
There are surfaces where that method is simply wrong. Limestone, cast stone, marble sills and lime mortar are calcareous: acid dissolves them, so a wash strong enough to shift the bloom will also eat the joints and dull the stone. On those, the answer is gentler and slower — repeated dry brushing, plain water, patience, and accepting that some deposit stays until the water source is dealt with.
Timing note: cleaning during a wet season often looks defeated within weeks, because the source is still delivering. Remove after addressing water, or accept a repeat.
Reading the warning
Persistent efflorescence in one zone points at its cause: failed guttering above, ground contact and rising damp below, a cracked cap or sill letting water in behind. Fixing that is plumbing-and-flashing territory, not cleaning — but the bloom told you where to look.
Treat recurring bloom as free diagnostics. Clean the wall, then follow the map it drew.
The pattern is readable if you look at the shape of it. A horizontal band low on the wall usually means water arriving from the ground — splashback off a hard surface, soil or mulch piled above the damp-proof course, a downspout discharging against the footing. A vertical stripe or a fan spreading downwards points at something above it: a joint in a coping, a failed sill, a gap behind flashing. A bloom directly under a gutter joint or a downspout usually is the gutter, and what a blocked gutter does to the woodwork behind it is happening to the masonry at the same time.
Stopping it coming back
Cleaning is the last step, not the first. Clear and reseat the guttering so the wall stops being rained on from above, extend downspouts so they discharge away from the footing, cut back soil and mulch that has crept up the wall, and repoint any joints that are open. Then clean, and then watch: a wall that stays clean through a wet spring has had its water fixed, and one that blooms again in March has not.
Two things not to do. Do not seal a damp wall — a coating that stops vapour escaping moves the crystallisation inside the brick, which turns a cosmetic problem into a structural one. And do not paint over the bloom, because paint applied to salt-laden masonry has nothing sound to bond to and lifts within a season. On most buildings the durable fix starts with the gutter cleaning nobody has done for three years.
Efflorescence in Southeast Missouri
The regional conditions are close to ideal for it. Wet springs soak walls repeatedly, mature tree cover and river-valley fog keep shaded elevations damp for days at a time, and freeze-thaw winters open joints and hairline cracks that give water new routes in. Older brick around Ste. Genevieve, Fredericktown and Cape Girardeau is porous and laid in lime mortar, so it absorbs and releases more water than modern masonry does — the same pore structure that makes graffiti harder to lift off brick than off concrete. More transport, more bloom.
Ozark limestone is the local complication. Limestone foundations, sills, caps and garden walls are common here, and they are exactly the surfaces an acidic wash will damage, so a wall of soft brick with limestone detailing needs two different approaches on the same elevation. Iron in local well water adds another wrinkle: on properties on a well, a white bloom and orange staining often appear on the same wall, and the orange half is a separate problem covered in why iron in well water leaves orange staining. Sprinklers and hose bibs fed from an iron-rich well will keep producing both until the spray is redirected off the masonry.
Common questions
Is efflorescence damaging the wall, or is it just ugly?
The deposit on the surface is cosmetic. The water bringing it is not. If the salts are crystallising inside the brick rather than on it, the face can start flaking, so a bloom that keeps returning in the same place deserves attention beyond cleaning.
Will it come back after you clean it?
If the water source is still live, yes, and usually within weeks of the next wet spell. That is the honest ceiling on cleaning alone. We will clean it and tell you what the pattern suggests, but the lasting fix is upstream of us.
Can I scrub it off myself?
Dry brushing on a small area is safe and worth trying — a stiff bristle brush, no water, on a dry day. Where it goes wrong is reaching for acid or a strong household cleaner without diluting or rinsing properly, which etches brick, bleaches mortar and does permanent damage to any limestone nearby.
Why does it appear in spring and disappear in summer?
Because it tracks water, not season. Spring rain loads the wall, then slow drying deposits salts at the face; a dry summer stops the transport and light rain can wash loose deposit away, so it looks cured. It is not cured. It is waiting for the next wet spell.
Our wall is new and blooming badly. Did the builder do something wrong?
Not necessarily. New masonry carries a lot of construction water, and losing it over the first year or two brings salts with it. What matters is whether it fades. A new wall that blooms less each season is drying out normally; one that blooms harder in the same spot every spring is taking water in from somewhere.
Send photos of where the bloom appears — we will clean it and tell you what the pattern suggests about the water. Read more about stain removal →