Rising damp, although a serious find in most homes, has a very simple cause; infiltration into the house by moisture. This article is going to look at the causes of rising damp, the best ways to prevent it & the cost to damp-proof walls.
Calculating the costs of damp proofing walls will depend on the length of the walls and the size of your home. The following table shows how many chemical injections each wall type requires.
|Type of Wall
||Amount of DPC chemical injected||Notes|
|4.5” single skin wall||1L per 9m||Injected from one side|
|9” cavity or double skin wall||1L per 4.5m||Injected from one or both sides|
|8” solid wall||1L per 2m||Injected from both sides|
Remember that the costs of materials will depend on the chemicals used and some will only be available for professional use because of the specialist equipment and training that are needed. Generally speaking, Dyzone cartridges will cost around £30 per ~310ml and for walls which are on the thicker end of the spectrum, you will require 600ml cartridges which will cost around £35 each.
The Causes of Rising Damp
The causes of dampness in a house are generally the product of moisture soaking through a wall or floor and the construction problems that have caused these. It does this by capillary action like a sponge. Water is naturally present in the outside world in the ground and from weather and the last thing you need is for this moisture to enter into your home and cause all the problems attributed to rising damp.
Houses are usually built from wood, concrete, stone or brick, either in layers or as one layer. These four materials are unfortunately naturally permeable to water and need to be waterproofed to stop the water ingress. The methods of waterproofing can vary depending on whether there is water ingress from outside or from below. If the ground level on the outside contacts the outside wall above the damp proof layer then moisture can bypass the damp proof course and work its way inside.
If there are damp patches above 1m from the ground level then it is most likely that you have penetrating damp instead of rising damp. This is where the moisture is forced through from the outside by various reasons but although similar, this type of damp is outside the scope of this article.
Whichever type you have, continued exposure of wood or masonry to moisture when it is not designed for it will eventually result in the breakdown of the structure of the building material and a subsequent reduction in strength. Continued problems will eventually cause severe damage to construction materials, internal finishes and decorations as well as damage to furniture and general health problems. All these will end up costing a great deal of money to restore or will cause severe respiratory problems that affect the quality of life. It makes sense to have damp problems repaired by a professional as soon as they become apparent rather than do a faulty DIY job as it will always cost more to leave it unattended.
The treatments will vary depending on whether there are damp patches on internal walls or whether you need damp proofing external walls or damp proofing concrete walls.
Damp proofing can be achieved by preventing the flow of water from one surface to the other by a number of methods.
- Using construction materials that are naturally impermeable to water or are so dense that water cannot cross. Materials like this are metal, plastic, chemically treated concrete and dense engineering bricks used in foundations.
- Building the wall of sufficient thickness so that the moisture cannot travel from the outside surface into the inner surface. In the UK, many country houses built before damp proofing was understood rely on having thick walls deeper than about 600mm to prevent water ingress. Although this is mainly a remedy for penetrating damp it also helps with rising damp.
- Building a double wall with an air break between, this is called a cavity wall. The moisture is confined to the outer skin and cannot reach the inner skin. When building the wall, it is important to make sure that no mortar falls into the cavity allowing moisture to bridge the gap.
- Placing a naturally waterproof membrane somewhere in the wall depending on where the moisture is most likely to show. If there is a free channel from the ground up through the wall material then a physical damp proof membrane (also known as a damp proof course or DPC) must be inserted. These are installed between the underground foundation concrete or dense foundation bricks and the less dense above ground, house bricks or wood. The usual DPC used here is a length of bitumen impregnated fabric or a thick polythene membrane. To comply with the UK Building Regulations a DPC will have to be installed at least 150mm above ground level,
- If you have problems with a damp proof course there will be symptoms showing up to about a metre above ground level. If so, remove all plaster to a level above 1m and then paint the surface with a waterproof liquid such as bitumen, tar or rubber based chemical that will dry and form a flexible damp barrier.
- Usually, the layer on a wall furthest from the outside is gypsum plaster. By the addition of certain chemicals when applying the plaster, it is possible to create a damp proof plaster. Other internal damp proofing solutions include painting the inner brick surface with a waterproof chemical before coating with gypsum plaster. This will provide an effective damp plaster treatment.
External Wall Treatment
It is no use treating rising damp until you have treated the cause otherwise the damp will simply reappear somewhere else.
There are many ways to treat rising damp in walls and these have been covered in general terms in the previous section. Having said this, by far the best way to provide damp wall solutions and prevent the need for damp wall treatments is to prevent moisture from coming into contact with indoor surfaces.
When to call out a rising damp specialist
If your house has either a non-existent or a damaged DPC you will have to have one retrofitted by a damp proofing contractor. Most damp proofing specialists make their living by installing a DPC in walls and floors by chemical or foam damp proof injection. They are usually the first stop for anyone whose house is suffering from rising or penetrating damp and will be able to give you estimates on their best average cost of damp proofing a house.
If you decide to choose a damp proofing specialist to inject DPC chemicals, he or she will follow some of the steps listed below. Obviously, each individual case will have to be assessed by a DPC professional first and a plan of operations drawn up for the most efficient application of the chemicals, but the following operations will give you an idea on what needs to be done.
- Survey the house, noting age, building material, the location of damp.
- If damp proofing internal walls, all affected plaster will be completely removed.
- If damp proofing external walls dig a trench alongside the wall to expose existing DPC if present. The ground level must be at least 150mm below the DPC level.
- Depending on the type of wall and wall material, drill injection holes to the required depth at the correct spacing.
- Inject the correct DPC chemical for the application into the holes at the correct pressure designed to fill up all cracks, fissures and capillaries in the wall.
- Plug the holes with suitable masonry.
- Paint internal walls with a waterproof and flexible layer.
- Replaster internal walls.
- Re-render external walls.
As you can see, the cost of rising damp treatment, as well as damp proofing costs in general, can be affordable if compared to the structural damage caused by moisture ingress. Your home is probably the largest single investment that most people make in their lifetime and it makes sense to look after it with the correct repair and maintenance regime. Don’t leave rising damp to its own devices, it will cost more in the long term.