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Understanding the Problem

What Is Rising Damp?

A plain-language guide to what's actually happening inside your wall — and why it keeps coming back.

Rising damp is moisture from the ground that moves upward through the porous materials of a building — particularly masonry and mortar — through capillary action.

"Moisture can move through the wall carrying dissolved salts. As the water evaporates, the salts are left behind in the wall and on the surface."

Moisture can carry dissolved salts into the wall, and when the water evaporates, the salts stay behind and build up in the masonry. This is why damp walls often develop salt deposits or efflorescence, and why the problem can keep returning even after the surface looks dry.

Cutaway diagram showing groundwater rising through a wall foundation by capillary action
Groundwater is drawn upward through the porous structure of masonry and mortar.

This capillary movement doesn't stop at ground level. As the illustration below shows, moisture continues rising through the wall until it reaches a point where evaporation outpaces the supply of new moisture — leaving hygroscopic salts behind in the masonry and, eventually, discolouration and flaking plaster on the surface.

Diagram showing rising damp moving from ground level up through a wall, with hygroscopic salts, floor level, and resulting discolouration and flaking plaster
As moisture rises above floor level, hygroscopic salts accumulate and surface damage follows.
Diagram showing the rising damp level in a wall, with evaporation and salt crystallisation occurring above it, compared to a wall section with a chemical damp-proof barrier
Above the rising damp level, evaporation concentrates salts within the wall — the stage at which visible damage typically appears.
The Technical Version

Water entering the masonry dissolves soluble salts and transports them into the wall fabric. When evaporation occurs, the salts crystallise and accumulate within the pores and on the surface.

This salt crystallisation is what makes rising damp different from a simple case of a wet wall drying out on its own. Because the salts are hygroscopic — meaning they attract moisture from the air — a wall can remain damp to the touch even during dry weather, and painted or plastered surfaces can keep failing even after repeated redecoration.

Causes

How Rising Damp Occurs

Rising damp occurs when ground moisture is drawn up through porous wall materials by capillary action — especially where the damp-proof course (DPC) is missing, has failed, or has been bridged.

Ground moisture
→
Foundation / wall
→
Mortar joints
→
Upward moisture movement
→
Damp wall

How It Works

Ground moisture

The water in the soil below or beside the building — the source of the damp that enters the wall.

Porous masonry

Brick, block, stone and mortar all contain tiny pores that can absorb water much like a sponge.

Mortar joints

Often the easiest route — the mortar-to-unit interface contains voids and capillary cracks that help water travel upward.

Capillary action

The suction force that pulls water up through these tiny openings, against gravity.

The DPC's role

A damp-proof course should stop that upward movement. If it's absent, damaged, or bypassed — by raised ground, render, plaster, screed or debris — the moisture can continue rising into the wall.

In Plain Language

Think of the wall as a bundle of tiny tubes. When the base of the wall stays wet, those tubes pull water upward until the wall becomes damp near the bottom. A working DPC breaks that pathway; a failed or bridged DPC lets the moisture keep moving into the wall fabric.

Signs of Damage

Signs of Damage Caused by Rising Damp

Rising damp can cause more than just a damp-looking wall. As moisture moves upward from the ground through porous masonry, it can carry dissolved salts into the plaster and wall finishes. As the wall dries, these salts can crystallise and gradually damage the surfaces.

01

Peeling or Flaking Paint

Paint may begin to bubble, blister, peel or flake, particularly along the lower sections of walls, as moisture and salts affect the bond between paint and plaster.

02

White Powdery Salt Deposits

White, powdery or crystalline deposits — known as efflorescence — appear on the lower wall when moisture carrying soluble salts reaches the surface and evaporates.

03

Crumbling or Powdering Plaster

Persistent damp can cause plaster to become soft, weak, powdery or crumbly, eventually losing its bond with the wall.

04

Blistering and Bubbling

Paint and plaster may bubble as moisture accumulates behind the surface. Repainting without addressing the source usually brings the problem back.

05

Damaged or Loose Plaster

Hollow-sounding, loose, detached or falling plaster — especially low on the wall — as surface deterioration progresses over time.

06

Damp or Discoloured Lower Walls

Dampness, staining or discolouration near the base of a wall, sometimes extending upward. Similar patterns can have other causes, so diagnosis matters.

07

Salt-Related Masonry Damage

Where salt accumulation is significant, repeated crystallisation can cause the masonry surface itself to flake, crumble or detach — known as spalling.

08

Damage to Skirting Boards and Timber

Persistent damp at the base of a wall can affect adjacent timber, contributing to decay where timber stays damp for extended periods.

The Important Point

Rising damp is not simply a cosmetic problem. If moisture continues to enter the wall from the ground, repeated painting or patching the damaged plaster may only conceal the symptoms temporarily. The moisture source needs to be correctly identified and addressed.

What This Actually Looks Like

Genuine, unedited photographs of the signs described above — plaster loss, discolouration and salt-related damage on real walls.

Plaster detachment on a wall and door frame, showing rising damp damage
Extensive plaster loss exposing bare masonry beneath painted wall
Exterior masonry wall with a band of plaster and paint damage near the base
Plaster loss on a wall corner near a doorway
Damp staining and drip marks below a window on an exterior wall
Plaster detachment near a window ledge
Wall plaster damage and staining near floor level
Exterior wall showing patch repair and discolouration from previous damp damage

Real, timestamped photographs — not stock imagery or illustrations.

Don't just repaint damp walls.

Peeling paint, white salt deposits, crumbling plaster and damaged lower walls can all be warning signs of moisture problems. Identify and treat the cause before repairing the damage.

Diagnosis

Rising Damp vs. Penetrating Damp vs. Condensation

Not all damp on a wall has the same cause. Rising damp, penetrating damp and condensation are three different moisture problems, and identifying the source matters because the right remedy depends on the cause. Dampness is also sometimes misdiagnosed, so visible symptoms should be treated as clues rather than definitive proof.

Feature Rising Damp Penetrating Damp Condensation
Where moisture comes from Ground moisture Rainwater or water entering through the building fabric Moisture in the indoor air
Typical location Lower sections of walls Walls, ceilings or around openings; location varies Mainly on cold internal surfaces
Typical pattern Usually starts at the base and rises upward Localised or irregular patches Often widespread on cold surfaces
Common signs Damp staining, salt deposits, peeling paint, crumbling plaster and damaged skirting Damp patches, staining, damaged finishes and sometimes mould Water droplets, condensation, mould and musty surfaces
Relationship with weather Generally not directly dependent on rainfall Often becomes worse during or after wet weather Often worse when indoor humidity is high and ventilation is poor
Common contributing factors Moisture drawn upward through porous masonry; a defective, absent or bridged DPC can contribute Defective roof, gutters, pipes, masonry, render, windows or other openings Poor ventilation, high indoor moisture production and cold surfaces
Main approach Stop or control rising moisture and deal with salt-contaminated materials Find and repair the route through which water is entering Reduce indoor moisture and improve ventilation and surface conditions

1. Rising Damp

Rising damp occurs when moisture from the ground moves upward through porous masonry by capillary action. It commonly affects the lower portion of a wall and may be accompanied by salts carried from the ground.

  • Damp staining near the base of walls
  • White or crystalline salt deposits
  • Crumbling or salt-contaminated plaster
  • Peeling or blistering paint
  • Damaged skirting boards
  • Deterioration of timber near the base of the wall

Important: rising damp should be properly diagnosed before treatment, because other sources of moisture can produce similar symptoms.

2. Penetrating Damp

Penetrating damp occurs when water enters through the building from outside — most commonly rainwater passing through defects in roofs, walls, windows, render, gutters or other parts of the building envelope.

  • Damp patches on walls or ceilings
  • Water staining
  • Dampness that becomes worse during wet weather
  • Damp around windows or other openings
  • Plumbing defects or leaking pipes within walls or floors
  • Deteriorated plaster or finishes
  • Mould or fungal growth in persistent cases

The key to dealing with penetrating damp is identifying and repairing the source of water entry.

3. Condensation

Condensation occurs when moisture in the indoor air comes into contact with a sufficiently cold surface and turns into water droplets. Poor ventilation can allow indoor humidity to build up.

  • Water droplets on windows and cold walls
  • Damp surfaces
  • Black or other mould growth
  • Musty smells
  • Staining or deterioration of finishes
  • Problems concentrated in poorly ventilated rooms such as kitchens and bathrooms

A Simple Way to Think About It

Rising Damp
Ground
→
Wall
→
Upward moisture movement
Penetrating Damp
Rain / external water
→
Defect in building
→
Inward moisture
Condensation
Indoor moisture
→
Cold surface
→
Water droplets

A damp wall does not automatically mean rising damp. The location, pattern of moisture, presence of salts, weather conditions and possible external or internal sources should all be considered. A proper investigation helps ensure that treatment addresses the actual cause rather than simply treating the visible symptoms.

Identify the type of damp before choosing the solution. Rising damp comes from the ground, penetrating damp comes from water entering through the building, while condensation comes from moisture in the indoor air. Correct diagnosis is the first step toward effective treatment.