Understanding Dampness and Condensation

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5 August 2019 - 14:21, by , in Waterproofing, Comments off

Dampness in Buildings

  • Roof leaks
  • Plumbing leaks
  • Condensation
  • High ground
  • Rainwater penetration
  • Defective rainwater goods
  • Flooding
  • Rising damp
  • Lateral penetration



Visual Evidence of Dampness

• Mould growth
• Deterioration of finishes, blowing/disintegrating plasterwork
• Liquid water on surfaces
• Staining of finishes
• Efflorescent salts on surfaces
• Timber decay
• Distorted timbers
• Dampness to finishes


The most common cause of damp in domestic properties remains

  • Condensation
  • Smelly
  • Wet
  • Destroys possessions
  • Looks awful
  • Health fears


Common Faults

  • Ground Water
  • Rainwater goods
  • Other Defects
  • Rising Damp
  • Blocked Gullies


Rising Damp

How are problems damp diagnosed?

  1. Visual appraisal
  2. Instrument readings
  3. Laboratory analysis

Correct diagnosis is vital!



Rising Damp Visual appraisal


Reproduced from BRE Digest 245 (2007) “Rising Damp in Walls: Diagnosis and Treatment


We could define rising damp as:

The vertical movement of water up through masonry, the water originating from ground water. The water rises through a series of interconnecting pores by a process called ‘capillarity’ – broadly, porous masonry acts like a ‘wick’.


Note: ‘Capillarity’ in building materials has nothing to do with or related to water rising in plants/trees. The rise of liquids from roots to leaves in plants is a process known as ‘cohesion’, not capillarity, and involves hydrogen bonding of water.



If the ‘suction’ of the wall is greater than the suction of the ground then water will rise – if not water will not rise

Salt concentration at top of rise ‘Salt band’ – most of the salts are hygroscopic

No significant/low salt levels at base!

Soluble chlorides, nitrates, sulphates and other mineral salts/soluble materials

Rainwater in the soil is the most prevalent source of water at the base of a wall – not water table


How do we treat Rising Damp?

  • Physical DPC insertion
  • Chemical injected DPC

Barriers to damp can take a number of forms. They all work using barriers to protect the internal finishes from water entering the building.

  • Electro Osmosis
  • EO Systems
  • Injection Mortar


Why Re-Plaster?

  • To remove hygroscopic material
  • To provide a dry wall surface
  • Prevent future deterioration
  • It forms part of “System”


Measuring Dampness in Buildings

Instrument readings

Electric moisture meter


• Non destructive – quick to use
• Easy to create “moisture profiles”
• Small and portable
• Valuable aid in the right hands


• Calibrated for use on wood – not masonry
• Can give misleading readings (e.g. contaminant salts, foil-backed paper, high carbon substrate)
• Often misused in the wrong hands


Moisture Analysis (Oven Dry Method)

The presence of Capillary/Free moisture in a material indicates a source of water ingress.


Damp Created Inside


The most common form of dampness in residential properties in the UK

Misdiagnosis & misunderstanding of condensation is common

It is widely accepted that we in the UK have a “condensation season”.

This is usually between October and April but is dependant on the outside temperature.

If there are significant dampness problems outside through the summer months, it is probably not condensation.

Condensation occurs when water changes from its ‘gaseous state’ to its ‘liquid state’.

This only happens when the air reaches a relative humidity of 100%

The point at which the water changes state as saturation occurs is known as the ‘Dew Point’.

  • All air contains some water vapour.
  • The amount of water that can be held in the air is dependant on the temperature.
  • The higher the temperature, the more water can be held in the air.
  • Surfaces are usually cooler that the air that surrounds them.
  • If these surfaces are cooler than the dew point, then water will condense out of the air


Surface Condensation

Condensation is deposited on any surface that is below the Dew Point.

Condensation can be deposited at the surface and is known as ‘surface condensation’

Or within a structure where it is called ‘interstitial condensation’


Where is the water from?

  • Atmospheric water coming out of its gaseous state
  • Water is released into the air from a number of sources associated with normal life and occupation.

Water from rising or penetrating damp is very unlikely to contribute significantly to a condensation problem.

If condensation is occurring the walls will be relatively cold. If the walls are cold then significant evaporation is unlikely.


Vapour Pressure

Pascal (Pa) of kilo Pascal (kPa) is the standard unit for measuring pressure.

1 hectopascal (hPa) = 100 Pa ≡ 1 mbar.

1 kilopascal (kPa) = 1000 Pa ≡ 10 hPa ≡ 10 mbar.


Diagnosis and Investigation

Obvious evidence of condensation problems:

• Mould Growth on walls ceilings
• Musty Smell
• Fungal Growth
• Water droplets on impervious surfaces
• Steamed up windows
• Decay to internal sections of timber window frames

Water will not condense out of the air unless temperatures are at, or below, dew point.

Mould growth can occur if high humidity levels are maintained for long periods.


Diagnosing Condensation

To determine if condensation is happening at the time of your investigation:

Air Temperature = Thermometer

Humidity = Hygrometer

Dew Point = Calculation

Surface Temperatures = Surface Thermometer

A MMS meter can do all these things in real time

Data Logging stations


Other things to look for

• Construction types
• Placing of Insulation
• Vapour proof materials within construction
• Ventilation Systems – condition & serviceability
• Evidence of the causes of atmospheric water


Combating Condensation

  • Improve ventilation – sweeps out moisture laden air and replaces with drier air from outside
  • Improve heating – make it constant, not intermittent
  • Reduce sources of moisture – clothes drying/cooking/bathing
  • Improve thermal properties of walls – keep dry (silicone?)
  • Dehumidifiers
  • Improve surface temperatures – insulate
  • Remove water vapour at source
  • Reduce vapour pressure and dilute damp air.
  • Positive pressure ventilation
  • Passive stack ventilation
  • Dehumidifier
  • Thermal lining
  • Mould removers and anti mould chemicals
  • Anti mould Paints
  • Modern can be effective against mould growth





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