Damp Proofing Treatments & Damp Proof Course's:Physical & Remedial - Chemical, Gel, Cream & Mortar Injection:
Covering: Richmond, Twickenham, Teddington & Hampton Areas.
Twickenham, St Margarets, Strawberry Hill, Whitton, Isleworth, Brentford, Kew, Syon Park, Richmond, Petersham, Richmond Hill, Mortlake, Sheen, Barnes, Putney, Fulham, Chelsea, Fulwell, Teddington, Kingston, Hampton Hill, Hampton Wick & Hampton.
Postcode Areas: TW1, TW2, TW3, TW4, TW7, TW8, TW9, TW10, TW11, TW12, TW13, TW14, SW3, SW6, SW13, SW14, SW15, KT1 & KT2.
Email: email@example.com / Phone or Text David on 07751 738 843.
What is a Damp Proof Course?
A damp proof course; or dpc, is a physical or remedial method; by which moisture from the ground is prevented from entering either the walls; or if present the concrete floor, of a property.
Why is a Damp Proof Course necessary?
Just as a home requires a roof and guttering to prevent rainwater penetrating into its structure; vertical penetrating damp, so does it requires a damp proof course at ground level to prevent moisture entering the building from the ground. See image below.
How moisture travels from the ground into a building:
The black arrows in the image opposite illustrate the movement of moisture from the ground into the mortar beds of a 9 inch solid wall typically found in Victorian and Edwardian properties.
I have chosen this type of property and an English bond for illustration purposes; throughout this website because it is generally pre 1920's properties that require remedial damp proofing works, if showing some or all of the following symptoms; above the skirting boards,
- Damp Patches.
- Blistering paint.
- Blistering plaster.
- Black Mould.
- Salt Deposits.
The sub floor area:
Note that the brickwork of the property is actually sitting in the ground. That is the section under the floor boards; the sub floor area. Because the brickwork of the sub floor is in direct contact with the ground, moisture can travel both laterally; lateral penetrating damp, as well as rise vertically; rising damp, into the wall of the building.
The Mortar Beds:
The major pathway for moisture absorption into a wall is through the mortar beds; the sand and lime or cement between the bricks, via diffusion. The movement of molecules from a region of high concentration to a region of low concentration. Latin; diffundere, to spread out.
Sand and Lime:
It should be noted that the mortar beds of Victorian properties; pre 1920, are usually a sand and lime mixture which is readily absorbing and acts like a wick or sponge, absorbing and holding moisture at a much greater rate than properties with sand and cement mortar beds, typically post 1920.
Types of Damp Proof Course's:
Although there are many different materials used to damp proof a property against moisture absorption from the ground there are only 2 types of damp proof course.
1: Physical Damp Proof Course's:
A physical or tangible; perceptible by touch, damp proof course is inserted into a buildings structure while it is being constructed and has been made from a wide variety of materials.
1a Plastic physical damp proof course:
Plastic has been widely used as a damp proof course in properties since 1920; see opposite, it is cheap, flexible and generally found in properties which have a cavity wall and a concrete ground floor.
1b Non Plastic physical damp proof course's:
Before the 1920's slate, asphalt, granite, bituminous felts, even sheets of lead or copper were sometimes used as a physical damp proof course in properties with a solid wall and a wooden floor.
2: Remedial Damp Proof Course's and Treatments:
Does your property require a remedial damp proofing treatment?
A remedial damp proof course; or damp proofing, is generally used when a property which does not have a physical damp proof course or where the existing damp proof course has failed, is suffering from one or more of the following symptoms above the skirting boards.
- Damp patches.
- High moisture readings.
- Decorative spoiling.
- Blistering paint and or plaster.
- Hygroscopic salt deposits.
- Black mould.
Does your property have a physical damp proof course?
Post 1920's properties: Generally have a physical damp proof course:
During the 1920's building practices changed; providing an inexpensive, long term and durable barrier against damp entering a building from the ground, by the introduction of plastic as a physical damp proof course for cavity walls and a damp proof membrane, for concrete floors.
It very unusual; or simply bad building practices, for a post 1920's to 1930's property not to have a physical damp proof course generally made from plastic. Ground floor damp problems are usually caused by, a bridging of the damp proof course, with the raising of driveways and flower beds or a build up of debris. Leaky guttering, plumbing and drainage defects can also cause isolated damp issues adjacent to the defect.
Pre 1920's with 2 to 3 beds: Generally don't have a physical damp proof course.
Pre 1920's two to three bedroomed terraced houses; most of which were built during the industrial revolution of the Victorian era; for low paid factory workers, generally don't have a physical damp proof course and mainly rely on air brick ventilation in the sub floor; under the floor boards, to evaporate moisture from the ground. If your property is suffering from any of the following symptoms. Damp patches, high moisture readings, decorative spoiling, blistering paint, blistering plaster, salt deposits, or black mould. Your property may require remedial damp proofing works. Ancillary re plastering and treatment to joists and floor boards in contact with damp walls, may also be required.
Pre 1920's with 4 to 5 + bedrooms:
The more expensive properties of this era generally have a non plastic physical damp proof course made from slate, asphalt or a bitimous material. Concrete plynths on walls, at the ground to wall intersections; to reduce splash backs, and a deeper sub floor to increase under floor ventilation. It is generally a bridging of the damp proof course, leaky guttering or drainage problems that cause damp issues in the more affluent properties of the pre 1920's.
How to evaluate if your property is pre or post 1920:
Looking at the Brickwork Bonds:
The picture opposite illustrates two walls with different brickwork bonds. To the left; where the door is, a Victorian solid wall using header bricks within the bond, marked by the red dots. To the right the wall; of the extension with the window, is utilizing a stretcher bond.
Stretcher Bonded single skinned wall / cavity wall:
The view of a brick as you are facing it; or how it is laid, gives rise to its classification. A brick laid like this is known as a stretcher.
Builders started using a stretcher bond, with a cavity wall in the 1920's. If your house is built with a stretcher bond, illustrated below.
.. You can assume it is Post 1920 and should have a cavity wall with a plastic physical damp proof course.
Header Bonded solid wall:
Turning the stretcher face of a brick 90 degrees (3 o'clock to 12 o'clock) changes its orientation to show the bricks Header face. The stretcher bonded walls above use header bricks only at the corners. The wall to the left is using bricks with their header face showing throughout the bond (indicated by red dots) not just at the corners. When you see header bricks throughout the bond of a wall you can assume your property is Pre 1920, with a solid wall and damp course provisions are subjective.
Summary guide: Does my property have a physical damp proof course?
Age of property.
Damp course provisions.
- Pre 1920:
- Pre 1920 :
- Post 1920:
- 2 to 3.
- 4 to 5 upwards.
- Generally no physical damp course.
- Generally a non plastic physical damp course.
- Generally a plastic physical damp proof course and membrane.
Summary guide: Does my property need a remedial damp proofing treatment?
Age of property.
Remedial Damp Proofing Required.
- Pre 1920:
- Pre 1920:
- Post 1920:
- 2 to 3.
- 4 to 5 upwards.
- Generally if showing any of the above symptoms.
- Unusual, but don't rule it out.
Exceptions to the rule:
Although cavity walls and a plastic physical damp proof course were widely used after 1920, some post 1920's properties have a solid wall and a non plastic physical damp proof course, also some Victorian properties do have a cavity wall, however they are quite rare and were generally only used in the more expensive properties.
Further reading and References:
An excellent article by Wikipedia about brickworks bonds.
Types of remedial damp proofing treatments:
There are various remedial damp proofing methods used to damp proof a property. The purpose of which is to provide a continuous horizontal or vertical barrier against moisture absorption from the ground, just like a physical dpc. The most commonly used methods are:
- 2a: Chemical Injection: Damp proofing treatment:
- 2b: Gel or Cream chemical Injection: Damp proofing treatment:
- 2c: Mortar Injection: Damp proofing treatment:
2a: Chemical Injection: Damp proofing treatments.
Chemical injection damp proofing treatments started having widespread use in the 1950's. They are quick and easy to install with little building knowledge being required by the operator who installs them and the chemicals used are very cheap, consequently they are used a lot by the bigger damp proofing companies.
Application of a chemical injection dpc:
Holes are drilled into the brickwork at an appropriate level; see diagram opposite, rods are inserted into the holes and a machine pumps chemicals (diluted with approximately 90% water) under pressure into the holes, the purpose of which is to provide a continuous horizontal or vertical barrier to moisture; along the mortar beds, just like a physical dpc as indicated by the red line.
Chemicals pumped under pressure:
The chemicals need to be pumped under pressure because the pores of the brickwork are very small, and it is hoped that the chemical will pass through them and saturate the mortar beds below.
Health and Safety:
In a nutshell chemical injection damp proofing chemicals are very dangerous to your health. As an environmentalist I do not advocate their use. Have a look at the datasheet of a typical injection chemical. Further reading. Note the section: Spillages into waterways must be reported to the Environmental Agency Incident Report Line.
2b: Gel & Cream chemical injection: Damp proofing treatments.
Gel and Cream injection damp proofing treatments have become very popular with the diy market recently because of their ease of use.
Application of a gel or cream chemical injection dpc:
Holes are drilled in a horizontal line into the top of the perpend joints; or known in the trade as the perps. Which is the vertical joint between two bricks. The holes are then back filled with a cream or gel.
Theory behind gel or cream chemical injection dpc:
After moisture has travelled horizontally along the mortar beds, it then passes vertically up the perpend joints in a snakes and ladders like fashion. The cream or gel prohibits the vertical movement of moisture along the horizontal line where the mortar beds are drilled.
Problems associated with chemical remedial damp proofing treatments.
- A: The majority of chemicals used are water based.
Therefore moisture from the ground will eventually dilute them rendering them ineffective.
- B: They leave unsightly holes in the brickwork when installed from the outside.
- C: They can bridge the internal plaster levels when installed from the outside (see below).
When installed from the outside the operator does not know the internal plaster levels, unless the skirting boards are removed. Internal plaster levels should not go below the level of the damp proof course, because the plaster will be touching a damp wall.
The diagram to the right, shows the plaster inside is below the level of the installed damp proofing treatment; red line. Therefore the plaster bridges the damp proofing treatment.
D: Susceptibility to brickwork and mortar bed irregularities within a solid wall.
The problems associated with brickwork and mortar bed irregularities when installing a chemical remedial damp proof course in a solid wall, are due to the walls construction, use of damaged bricks on the inside of the wall and competence of the bricklayer(s) building the property.
On the outside of a wall the good face of a brick is used and the mortar beds are neatly pointed and evenly spaced; image to the left. However from the images to the right of the inside of a solid wall you can see that the mortar is thicker in places, especially where there are corners and intersections. Also you will notice that a lot of the bricks are damaged at the corners, some are actually cracked. This is because bricklayers basically used damaged and off cuts of bricks, on the inside of the wall, especially underneath windows, where the load of the building is supported by the windows lintel. From experience at least 40% of the headers in older properties are not full bricks, they are half or quarter bricks; the offcuts.
To illustrate this point the diagram opposite shows the front and above elevations of an English Bonded solid wall, which consists of a stretcher course, then a header course. Diagrammatical representations of walls always show complete bricks to illustrate the bond. However the diagram of the above elevation of the Header Course, shows the reality that: Many of the header bricks in a solid wall are actually, offcuts of bricks and the void where a brick should be is filled with mortar.
Impregnation of the mortar beds:
Chemical injection damp proofing treatments have to totally impregnate the mortar beds below the injection point to provide a continuous barrier to moisture. Because of the varying widths of the mortar beds on the inside of a solid wall, especially at the perpend joints and the mortar voids created by the use of off cuts of bricks; especially the headers, there will always be areas where the chemical does not totally impregnate the mortar beds making the treatment ineffective in many areas of the wall. I would estimate that at least 50 percent of the remedial treatments I undertake, are on walls that have previously had a chemical injection damp proofing treatment, that has failed within 10 to 15 years of instillation.
Party Wall brickwork and mortar bed irregularities:
Although most of the diagrams on this web site show the front elevation of a property, party walls are also sitting in the ground, and the use of damaged and offcuts of bricks is greater because the face of both sides of the wall are not showing; the walls are covered in plaster.
2c: Mortar Injection: Remedial damp proofing treatments.
Mortar injection remedial damp proofing treatments use a plasticized cement based mortar that is impervious to water.
Application of a mortar injection damp proofing treatment:
Utilizing the same principles as the gel or cream injection holes are drilled in the perpend joints just like gel or cream chemical injection but the holes are back filled with the plasticized mortar to prevent the upward flow of moisture.
Advantages of mortar injection:
- Because the mortar is not a water based chemical, cream or gel, it is not broken down by moisture rising from the ground, and should therefore last as long as a plastic physical damp proof course.
- Voids caused by brickwork and mortar bed irregularities can be filled by simply removing the mortar bed.
References and Further reading:
Also have a read about the
movement of moisture
from a very intelligent chap.
G.R. Coleman B.Sc(Hons)., M.S.B., C.Biol., M.I.W.Sc..
- Member of the Institute of Wood Science. (M.I.W.Sc.)
- Member of the Institute of Biology. (M.S.B)
- Chartered Biologist (C.Biol.)
- Consultant Member of the Property Care Association (formerly British Wood Preserving and Damp-proofing Association) - Honorary Life Member.