Moisture absorption into a building from the ground:
Lateral Penetrating and accompanying Rising Damp is very distinctive, as can be see from the images opposite. If present you will have one or more of the following symptoms above the skirting boards.
Please note the operative phrase is. "Above the Skirting Boards".
Symptoms of Rising & Laterally Penetrating damp:
- Blistering paint, wallpaper or plaster.
- Dark and damp patches on paint, wallpaper or plaster.
- Salt deposits.
- Black mould growth.
- A sudden cut off, when vertical moisture readings are taken.
The above symptoms will be exasperated in areas when works such as those listed below were conducted near ground level and incorrect building materials and methods were used.
Fitting skirting boards & electrical back plates.
Kitchens & Double Glazing.
Alterations, modifications & conversions.
Incorrect use of Bonding Plaster:
It should be noted that the use of bonding plaster as an undercoat and making good plaster in solid walled properties can cause severe dampness and black mould. Bonding plaster contains cork particles which makes the plaster very absorbent to moisture. Sand and cement or a renovating plaster should always be used.
Dampness caused by incorrect building methods and materials:
The images above show a property which was renovated incorrectly with both, methods and materials used.
- The plaster is touching a concrete floor, which does not have a damp proof membrane.
- Bonding plaster was used instead of sand and cement as an undercoat plaster.
Cause of Rising Damp:
Damp rising into a building is very easy to understand. If you sleep in a tent without a ground sheet you will wake up with a damp sleeping bag. Moisture has risen or being absorbed from the ground into your sleeping bag.
However your house is not sitting on the ground, it is sitting in the ground, as you can see from the diagram opposite. Unless building measures; such as a damp proof course, are taken to prevent vertical and lateral penetration of moisture from the ground, it will rise into the building.
Movement of moisture through a wall:
You can always spot a bad damp proofing company or someone who pertains to know about damp proofing, but doesn't, because they will tell you damp rises up the wall, through the brickwork, via capillary action.
Although moisture does rise through the brickwork of a wall via capillary action. The major pathway for moisture absorption from the ground is via diffusion, through the mortar beds, the mortar between the bricks, not the brickwork. Ask yourself the question how does moisture get from one brick to another?
Sand and Lime Mortar Beds:
It should be noted that the mortar beds in older properties; pre 1920 Georgian, Victorian and Edwardian generally consist of a sand and lime mixture which is very porous and readily absorbing.
Moisture will flow and rise via any absorbent material, simply place a sponge or a beer mat of Stephen Fry; in an upright position, into a cup of water and observe.
Within a wall the most absorbent part is the mortar beds which will feed moisture absorption into the brickwork, which will both feed absorption into the plaster. Leaving damp patches and spoiling decorative finishes as the moisture evaporates and also provide a breading ground for Black Mould. Over a prolonged period the evaporation of moisture will be associated with the blistering of paint and plaster. It can also leave hygroscopic salt deposits, namely chlorides and nitrates which attract moisture from the atmosphere.
Under the floorboards:
The area underneath the floorboards is called the sub floor, it is a void of between 18 inches to over 4 feet in depth, sometimes so deep it becomes a cellar. Rather like hanging your clothes on a washing line, air comes into the sub floor via the air bricks, assisting with the evaporation of moisture that has been absorbed into the wall, before it reaches the ground floor living area, simply take a floor board up and feel the draught.
Properties that suffer from rising and laterally penetrating damp issues are generally pre 1920's properties which do not have a physical damp proof course and primarily rely on air brick ventilation to evaporate moisture.
Damp Course provisions in pre 1920's properties:
After 1920 building regulations and how a house was constructed had started changing. Before 1920 most properties had a solid wall with a wooden floor and damp course provisions were subjective. After 1920 almost all properties had a cavity wall with a concrete floor and a plastic physical damp proof course.
Two to Three bedroomed: Pre 1920's properties:
During the reign of Queen Victoria 1837 to 1901, the industrial revolution brought about a housing boom, resulting in millions of 2 to 3 bedroomed terraced homes being built. In most cases they have one thing in common. Inadequate provisions to stop the movement of moisture from the ground into the ground floor living area. They generally don't have a physical damp proof course. In most properties the only provision these properties have against rising damp are the air bricks which vent air into the sub floor. A neat little trick though is the presence of air bricks in the party walls, which causes air to flow down the street.
Although this method does greatly assist with evaporation in the sub floor area, after time; 180 - 95 years, its effectiveness is reduced, because of the slow build up of moisture in the readily absorbent sand and lime mortar beds. Also when properties are renovated, a plaster called bonding plaster, containing cork particles, which absorb and retain moisture, is inadvertently used by builders in ground floor conversions.
In 1892 Thomas Worthington refereed to these properties as; "The Dwellings of the Poor" and "Weekly Wage-Earners in and Around Towns", conjuring up an image of Lowery, Doncaster and a flat cap, quite a different picture to that created by London Estate agents, aptly naming such dwellings as Cottages.
Other Factors which increase dampness in 2 to 3 bed pre 1920's properties:
- The sub floor area is generally small, therefore reducing ventilation in the sub floor.
- The mortar beds are a readily absorbent sand and lime.
- The front garden is usually very small or just a pavement, therefore reducing drainage away from the property.
- No protection at ground level against rainwater splashbacks at the ground to building intersection, because of the absence of a concrete plynth.
- A very small difference between the exterior and interior ground levels. **
Four bedroomed and upwards: Pre 1920' properties:
The more expensive 4 to 5 + bedroomed properties generally have a physical damp proof course made from slate, asphalt or a bituminous material and other contributing factors to prevent moisture absorption from the ground into the building.
- A deeper sub floor area, causing increased ventilation and therefore moisture evaporation.
- A denser mortar mix between the bricks, the major pathway for moisture movement is via the mortar beds.
- A greater difference between the interior and exterior ground levels. **
- A long front garden assisting in drainage.
- Greater protection at ground level against rainwater splashbacks at the ground to building intersection, with the use of a concrete plynth.
- ** Damp does not usually rise more than a meter. Therefore if you have a difference of one meter between the exterior ground level and the internal floor level, (which means big steps, leading to the front door), the damp will evaporate before it reaches the internal ground floor level.
Damp issues with very large: Pre 1920's properties:
There are also problems with both vertical & lateral penetration and rising damp in the lower ground floor (basement, cellar) area of very large properties because this was the area where the servants lived. The archetypal "Upstairs Downstairs". Also the area underneath the external concrete staircase of the entrance to these properties; generally where the gas and electric meters are is prone to: Vertical penetrating damp from cracks where the stairs intersect with the wall. Lateral penetrating damp where retaining walls of the staircase sections come into contact with the ground, and rising damp generally where the wall adjacent to the lower ground floor entrance is.