Dampness in a home is a chronic and often harmful issue that can cause damage to the structure, problems with how it looks, and even health issues. A key part of architecture called the damp proof course is at the heart of stopping this sneaky problem, especially rising damp. This simple but very effective barrier is built into most homes. It works as a horizontal shield to stop moisture from the ground from rising into the building’s structure. If you don’t have a damp proof course that works properly, walls can become wet, which can cause many problems that are expensive to fix and bad for living conditions.
An important part of a damp proof course is that it doesn’t let water through. The whole thing is meant to stop water from moving through it through capillary action. Water is drawn up through tiny holes in porous materials through a process called capillary action. This works a lot like how a sponge soaks up liquid. Bricks, mortar, and concrete are all porous by nature. If nothing was done, ground water would slowly rise and soak the lower parts of walls. This path is blocked by the damp proof course, which makes a line that water can’t cross. This protects the building above.
The way that a damp proof course is built has changed a lot over the years. In the past, pieces of slate were often used because it wasn’t porous naturally and worked well as a barrier. Bituminous felt, plastic membranes and more recently chemical injections have become the standard ways to make a strong damp proof course as building methods have improved. Even though each material is made of different things, they all work together to keep water out of the wall.
The building rules say that a damp proof course has to be included in every new home. Usually, this is put in place at least 150 mm above the ground level outside. With this important height, splashback from rain or watering the yard won’t be able to cross the damp proof course and let water get through the barrier. To make sure there is full security, the damp proof course should go all the way across the width of the wall, including any gaps. The damp proof course will only work for a long time if it is installed correctly.
A damp proof course may not work as well as it used to for a number of reasons over time. Bridging is a common problem that happens when the ground level outside rises above the damp proof course or when the floor level inside makes a way for water to get around the barrier. This can happen when soil builds up, when paving is put down, or even when the yard landscape is changed. When there is bridge, the damp proof course doesn’t work anymore because water can just go over the top and into the wall above.
The damp proof course could also have problems if it starts to break down. Modern materials last a very long time, but older ones, especially those in homes that were built decades ago, can break down. It’s possible for bituminous felt to become hard and crack, or for older chemical injection ways to stop working. When the structural stability of the damp proof course is compromised, it loses some of its ability to keep water out, which causes rising damp to show up inside the property.
To find a broken damp proof course, people usually have to look for certain signs inside the house. There may be rising damp if the lower parts of the walls have a tide mark, the wallpaper is coming off, the paint is bubbling, there is a musty smell, or salt deposits are forming on the plaster. These hygroscopic salts take in water from the air when they come in contact with wetness. This keeps the damp problem going even after the source of the rising damp is fixed. Often, a full check by a trained professional is needed to be sure that the damp proof course is really the problem.
When fixing a failed or bridged damp proof course, the reason is usually what needs to be fixed. If crossing is the problem, you need to lower the ground levels outside, make sure there is drainage, or make sure the floor levels inside don’t cross the damp proof course. A new damp proof course may need to be put in place where the old one has failed because of wear and tear. A chemical cream or liquid is often injected into the mortar course at the right level to do this. The chemical then spreads through the cement, making a new barrier that doesn’t let water through.
Putting in a new chemical damp proof course is a specialised job that needs to be done carefully. At the right level for the damp proof course, holes are made every so often along the mortar joint. The chemical, which is usually a mix of silane or siloxane, is then pushed or flowed through these holes by gravity. There is a new, invisible damp proof course inside the wall when this chemical mixes with the stone to make a water-repellent resin. The right choice of chemical and the skill of the worker are very important for this method to work.
In addition to installing the new damp proof course, there are often other steps that need to be taken to fully fix the damp problem. Hygroscopic salts can stay in the plaster even after the source of moisture is taken away. This means that contaminated plaster generally needs to be taken out and replaced with a damp-proof render and plaster. This makes sure that any salts that are still there don’t keep pulling water from the air. This lets the wall dry out fully and stops the damp problem from happening again. This all-around approach is very important for solving problems with the damp proof course in the long run.
It is important to tell growing damp apart from other types of dampness, like penetrating damp or condensation. Sometimes the effects that can be seen look the same, but the reasons and solutions are different. When water comes in from the outside through broken drains, render cracks, or bad pointing, this is called penetrating damp. Poor airflow and high humidity can lead to condensation, which is an inside problem. The damp proof course focuses on rising damp, so it’s important to get the diagnosis right for the treatment to work.
To sum up, the damp proof course is an important part of keeping any building from rising damp, which is a common problem. It is an impermeable barrier that is put in a way that keeps ground moisture from rising up into building walls. The damp proof course’s goal has always been the same, from its early days to current chemical injection methods: to keep the inside of a building dry and healthy. To keep your home’s structure and comfort in good shape, you need to know how a damp proof course works, how to spot the signs that it’s failing, and how to fix the problem.