1: Rising & Laterally Penetrating Damp:
Rising and laterally penetrating damp issues usually effect pre 1920's
Georgian, Victorian and Edwardian properties, which do not have a
physical damp proof course. Or where the existing damp proof course has
failed, been breeched or altered.
Symptoms of rising & laterally penetrating damp:
If present you will have one or more of the
following symptoms on the ground floor above the skirting boards
or in a basement or cellar.
- Blistering paint and plaster.
- Dark and damp patches on walls.
- Salt deposits, which attract moisture.
- Black mould growth.
Arrange a survey:
As you can see from the images opposite of poor Jo's kitchen in Teddington, rising and laterally
penetrating damp is very distinctive. If you have any of the above symptoms above the skirting boards
or in your cellar or basement please call David on 07751 738 843 to arrange a survey.
The following section illustrates how moisture from the ground enters a building. The
Damp Proofing section illustrates how moisture from the ground
is prevented from entering a building.
Movement of moisture into a building:
The diagrams opposite illustrate the movement of moisture from the ground into the
mortar beds, of a typical Victorian or Edwardian property with a 9 inch solid wall
and sand and lime mortar beds; the mortar between the brickwork.
The mortar beds:
Although moisture does flow into the brickwork of a building via capillary action, the major movement of
moisture from the ground; into a building, is via
diffusion; into the mortar beds. The
mortar between the brickwork. Acting like a sponge, the readily absorbing beds of sand
and lime absorb moisture both:
- Horizontally: Lateral Penetrating Damp and
Into the walls of the building from the ground.
The movement of a substance from a region of high concentration to a region of low
concentration. Latin "diffundere";
to spread out.
cannot jump from one brick to the other,
there has to be a continuous pathway for the movement of the moisture being absorbed
into a building. This continous pathway is provided by; the mortar beds, which in
older properties is usually a readily absorbing sand and lime mixture.
The amount of moisture that flows into a building via
is very small.
The Sub Floor:
Underneath the floorboards of a solid walled building; unless it has been covered by concrete, is an area called
the sub floor. The sub floor is a void of 18 inches to 4 feet in depth. In some properties the sub floor becomes
a basement or cellar.
As you can see from the cross sectional view far right: The brickwork;
of the sub floor, is below ground level and in direct contact with the ground.
Moisture can readily diffuse laterally across the mortar bed, then rise vertically. Providing a major
pathway for moisture absorption; from the ground, into the building.
Air brick ventilation in the Sub Floor:
If you imagine the sub floor area of your property like a small cellar or basement; a void of nothing,
18 inches to 4 feet deep running underneath your house.
Although the retaining walls of the sub floor are in direct contact with the ground. Outside the
property just above ground level are air bricks, which allow air to vent into the sub floor.
In some terraces the air bricks are also in the party walls so the air can circulate down the
Purpose of air bricks and a sub floor:
The sub floor allows vented air to circulate underneath your home assisting with the evaporation
of moisture absorbed into the walls, before it reaches ground level. It helps keep timbers dry and
free of wee beasties eating your floor boards and there is also the accommodation it provides for
pipework and cables.
Outlets for absorbed moisture:
The diagram opposite shows the outlets for moisture which has
been absorbed from the ground, via the mortar beds of the sub floor retaining
- A: Some of the moisture will evaporate within the sub floor or if present the basement or cellar.
- B: Some will pass into the timbers that are in contact with the wall.
- C: Some will pass into the ground floor plaster. Causing dampness,
decorative spoiling and the blistering of paint and or plaster as it evaporates.
- D: Some will evaporate outside.
- E: Some will jump on the floor and do a lap dance.
External ground levels above the existing damp proof course:
Lateral penetrating and accompanying rising damp can also be a problem in
properties that have a physical damp course. Problems can occur where there has
been a build up of debris, raising of driveways, flower beds, etc above the existing
physical damp proof course.
Problems caused will be adjacent to where the damp proof course has been bridged and the
construction of the wall will dictate how severe the problem is. A cavity wall has a gap (the cavity) making it more difficult for
moisture to pass into the ground floor. Whereas a solid wall has no cavity and moisture will readily pass
laterally and vertically into the ground floor of the property.
However you should always check to see if external ground levels are above
the damp proof course and also if there is a
drain or a leaky down pipe near
Rising Damp and Black Mould Growth:
It has been documented that the presence of
hygroscopic salts, which are associated with rising damp, kill
black mould, implying that if black mould growth is present
your growth is caused by condensation,
not rising damp.
However this is not always the case as can clearly be seen
in the images above of
poor Jo's kitchen. Black mould growth can be caused by ground floor
moisture absorption. Being found above skirtings in corners and areas of
Also the amount of salts contained within the absorbed moisture does vary upon geographical area,
water table and building materials.
What is a Damp Proofing Course:
Imagine you are sleeping in a tent without a ground sheet on the
ground to stop moisture rising into your sleeping bag. Obviously you will wake up in the morning
with a damp sleeping bag. To damp proof your tent against rising damp you simply put a plastic ground
sheet on the ground. A modern damp proof course is essentially a piece of plastic
which the house is built on top of.
Types of Damp Proofing Course:
A: Physical Damp Proofing Course:
A physical damp proof course is made from
plastic or in older properties, they are usually constructed from slate or asphalt. They are inserted into the
property when it is being built.
B: Chemical Injection: Damp Proofing Course:
Very popular with big damp proofing companies because the chemicals
used are cheep and very little building experience is necessary to undertake
The main drawback with this type of damp proof course, is that the chemicals used
are water based and over time usually 20 years, rising
and laterally penetrating damp will dissolve the dpc rendering it ineffective.
C: Gel & Cream Injection: Damp Proofing Course:
The major pathway for moisture absorption from the ground is
via the sand or lime and cement mortar between the bricks. Gel injection involves
drilling a series of holes in the mortar beds and back filling the hole with
a chemical gel.
This type of dpc has become popular with the diy market because
of its ease of use, however I have used gels in the past and although they are
moderately effective in some properties, I don't advocate their use in properties with a sand and lime mortar bed.
D: Mortar Injection: Damp Proofing Course:
Mortar Injection, is by far the most effective method I have
used, one drills holes; as with the gel injection, into the mortar beds, but
the holes are back filled with a plasticised mortar, which does not deteriorate
Advocation of unnecessary works:
I do find that customers are often confused about damp issues
in their homes and damp proofing companies do tend to dramatize the problem.
Causing confusion and fear. I have also found that
the advocation of unnecessary works is a problem widely associated with damp
In most cases salesmen; not builders or surveyors, are who recommended; albeit, trusted damp proofing companies
will send for your survey. Obviously they are interested in their commission and
limited building knowledge.
"Which" done a very good "Rogue Traders" type of report.
The report scored the bigger damp proofing companies as follows:
- Peter Cox 2/3.
- Rentokil 2/3.
- Kenwood 1/3.
- Lifecote 1/3.
- ProTen 1/3.
- Timberwise 0/3