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What are you seeing?

White salts

White crystalline deposits are usually soluble salts left behind as moisture evaporates through masonry or plaster. They are a clue to moisture movement.

Diagnose this symptomCompare likely causes
Recognise the pattern

Does your white salts look like this?

Use several clues together. A single stain or reading rarely proves the cause.

01White powder or crystals
02Often on brick, block or plaster
03May return after brushing away
What could be behind it?

Compare the most likely cause families

The same visible symptom can have very different causes. Look for the clue that best fits timing and location.

Explore all problems
1

Moisture moving through masonry

Compare this possibility with weather, room use, height and any nearby services before acting.

2

Low-level damp or bridging

Compare this possibility with weather, room use, height and any nearby services before acting.

3

Historic wetting followed by drying

Compare this possibility with weather, room use, height and any nearby services before acting.

Do this before buying a fix

Three useful checks

1
Check where the salts start and stopAdd the result to the overall pattern rather than treating it as proof on its own.
2
Inspect external ground levelsAdd the result to the overall pattern rather than treating it as proof on its own.
3
Avoid treating salts alone as proof of rising dampAdd the result to the overall pattern rather than treating it as proof on its own.
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DampDeck symptom guide

White salts: what to know

What it can mean

Efflorescence shows soluble salts have moved with moisture through porous material; it is evidence of moisture movement, not proof of one diagnosis.

Three useful questions

  • Where on the wall are the salts?
  • Has the wall recently dried after a leak?
  • Is masonry exposed externally?

Do not choose treatment from the symptom alone

The same visible symptom can come from different moisture sources. Use timing, position and nearby building/plumbing details to narrow it down.

Evidence & reviewDampDeck reviewed this guidance on 3 September 2026. UK government guidance says damp and mould should be addressed by identifying and correcting the underlying moisture cause; surface mould removal alone does not prevent recurrence.UK Government source →
Continue the diagnosis

Related DampDeck guides

Rising dampLow-level masonry moisture that needs evidence and careful exclusion of more common lookalikes.Read next →Penetrating dampRainwater or external moisture entering through a defect in the roof, wall, opening or rainwater system.Read next →
Investigate before treating

Three questions that narrow it down

1

Where on the wall are the salts?

2

Has the wall recently dried after a leak?

3

Is masonry exposed externally?

What can sit behind this symptom

Compare the likely moisture routes

The symptom tells you where to look. Timing and building context help identify why it is happening.

Condensation & humidityPossible causeCondensation & humidityMore likely when the surface is cold and the pattern is seasonal.Explore →Rain penetrationPossible causeRain penetrationMore likely when the patch changes during or after wet weather.Explore →Plumbing leakPossible causePlumbing leakMore likely around water services or where the weather makes no difference.Explore →
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Useful products for this stage

Only products that support the investigation or an appropriate fix are shown here. An active leak or building defect still needs repairing.

Digital hygrometerRelevant productDigital hygrometerBrowse on Amazon →Building moisture meterRelevant productBuilding moisture meterBrowse on Amazon →Protective cleaning glovesRelevant productProtective cleaning glovesBrowse on Amazon →
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Useful products for checking or controlling the conditions

Products can help measure, ventilate, dry or clean. They should not be presented as a substitute for fixing an active leak or building defect.

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Relevant to White salts

Moisture investigation

DampDeck only surfaces products that make sense for this stage of the investigation. Products do not replace diagnosis or repair of an active leak.

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Professional help

Find the right specialist once the likely cause is clearer.

Search locally by town or postcode instead of choosing a treatment from the symptom alone.

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