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Cross-market term

Efflorescence

A whitish deposit left on a surface when water carrying dissolved salts evaporates from it. The deposit is a symptom of water movement, not of the material being defective.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Kingdom

    Same word, different thing

    efflorescence

    also lime bloom, white staining, new build stain, saltpetring

    LIME BLOOM is a different deposit — calcium carbonate from lime leaching out of fresh mortar or concrete — which is harder to remove and does not simply wash away as ordinary efflorescence does.

  • Australia

    Same word, different thing

    efflorescence

    also salt attack, fretting, white bloom

    SALT ATTACK names the damaging case where crystallisation erodes the masonry, so the Australian term often implies harm where the British word implies a stain.

  • United Statesyours

    Close, not identical

    efflorescence

    also whiskering, bloom, new building bloom, subflorescence

    SUBFLORESCENCE is named separately and is the one that matters: the same salts crystallising just below the surface, where the pressure spalls the face instead of staining it.

  • Canada

    Close, not identical

    efflorescence

    also bloom, subflorescence, salt deposit

    As the United States, with de-icing salt adding a second source that has nothing to do with the masonry's own chemistry.

The governing standard, by market

  • United Kingdom

    BS EN 771-1 / BRE Good Building Guide

    Clay masonry units including active soluble salts content categories, and guidance on removing deposits without damaging the masonry.

  • United States

    ASTM C67 / ASTM C1400

    Sampling and testing brick including an efflorescence test, and the guide to cleaning existing masonry.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Brick Calculator →Tuckpointing Mortar Repair Volume Calculator →Manufactured Stone Veneer Mortar Coverage Calculator →

Frequently asked questions

Is efflorescence a sign of a damp problem?
It is a sign of water MOVING, which is not the same thing. Salts do not travel on their own: they dissolve in water inside the material, get carried to a face where the water evaporates, and are left behind. So a deposit tells you water has been in there and has come out here — and on a new wall that is completely normal, because the construction water is drying out and takes a season or two to stop. What makes it a problem is a deposit that keeps returning in the same place year after year, because that means a continuing supply of water rather than the building drying once. The right response is therefore not to attack the deposit but to ask where the water comes from: a leaking gutter, a bridged cavity, ground level above the damp-proof course, a failed flashing. Treat the stain without answering that and it comes back.
Why does washing it off make it worse?
Because water is the transport, and a hose supplies more of it. Wetting the wall dissolves the deposit and carries it straight back INTO the masonry, where it waits for the next drying cycle and comes out again — usually looking worse, because more salt has now been mobilised from deeper in. The same mechanism makes pressure washing actively harmful: it drives water in hard, and on a soft brick or lime mortar it also erodes the face, giving the salts a rougher surface to sit on. The recommended order is the opposite of instinct: brush the dry deposit off with a stiff bristle brush, let the wall go through its drying season, and repeat. Where a chemical clean is genuinely needed it is done on a pre-wetted wall with a controlled rinse, because the pre-wetting is what stops the cleaner itself being sucked in.
When is a white deposit actually serious?
When it is crystallising behind the face rather than on it, or when it is not efflorescence at all. SUBFLORESCENCE — the American term for the same salts depositing just under the surface — exerts pressure inside the pores as the crystals grow, and that pressure spalls the face off. The tell is a surface that is powdering, flaking or losing its skin rather than merely looking white. The second case is SULFATE ATTACK, where sulfates in solution react with the cement in the mortar itself: the mortar expands, joints crack and the wall can grow measurably taller, and no amount of cleaning touches it because the damage is the chemistry rather than the deposit. The third is LIME BLOOM, calcium carbonate rather than a soluble salt, which does not wash off because it is not soluble in water. Each needs a different answer, so identifying which one is on the wall comes before deciding anything.