What Is a Damp-Proof Course?

If you've been seeing signs of rot and mildew in your home, then you're probably due for a damp-proof course. But what in the world is a damp-proof course, and how will it help you solve your problem?

Well, if you're ready to find out the answer, let's start from the beginning!

Damp proofing Rising damp

What Is a Damp-Proof Course?

To put it simply, a damp-proof course, or DPC in short, is a material applied to buildings and houses to prevent the movement of water through their walls, floors, and roofs.

Now, DPCs are necessary for buildings that are sensitive to moisture. But what does a DPC achieve, and what will happen if you don't have one in your home? Well, let's get down to it, shall we?

What Can Cause Dampness in a Building?

Several factors can cause dampness in buildings, from the surrounding air and rain to the external ground.

How exactly? Well, as you know, soil contains a certain degree of moisture. Due to capillary action, this moisture can be absorbed by the porous elements of brick and concrete walls. And with enough time, you'll start finding signs of this rising dampness at floor-level walls.

Buildings can also suffer from what's known as penetrating dampness, which is when water travels through the walls from the outside. In most cases, this is due to the rain, but it can also be due to leaking roofs, faulty drain pipes and guttering, or something as simple as a crack in the wall.

But what if your area doesn't get much rain? Well, you can still get dampness in your building due to atmospheric condensation. Essentially, this is when water vapour transforms into water due to a drop in temperature.

Other than the rising dampness, penetrating dampness, and condensation, here are a few more reasons your building can be suffering from water damage:

  • Faulty building design and construction
  • Sunken floors or shoddy tile installation that lead to water collection
  • Leakage through roof slabs
  • Flattened roof slopes that collect water
  • Faulty plumbing in bathrooms and kitchens 
  • Outside vegetation near the building
  • Poor-quality concrete that's highly porous

How Does Dampness Affect Your Building?

If you're wondering what some dampness can really do to a building, well, quite a lot of things, actually.

For one, the dampness can cause unsightly patches on your walls and ceilings. It can also damage the wall paint and decoration, ultimately ruining the look of your house. 

But it's not just the aesthetics you should be worried about. Dampness can also soften your plaster walls, causing them to weaken and crumble. Moreover, it can damage the timber fittings and cause the metallic ones to rust and corrode.

The floors can also take quite a good beating from some moisture. Not only will the floor coverings be ruined, but the flooring can also become loose. That's because the water will damage the adhesive keeping the floorboards together.

Still, the worst thing dampness can do to your building is cause efflorescence. Over time, this will cause the disintegration of the bricks, tiles, and stones of your building. Unfortunately, this means that your building will become considerably weakened and liable to collapse in certain areas. 

A few other effects of dampness include:

  • Damage to electrical fittings, leading to electricity leakages and short-circuiting
  • Giving rise to unhealthy living conditions
  • Promoting mosquito and termite growth
  • Promoting disease-inducing germs such as those of tuberculosis

Popular Damp-Proofing Methods Explained

Several different methods are available nowadays for damp-proofing houses. Here are a few of the most popular ones.

Damp-Proof Membranes

Damp-proof membranes are water-repellent materials inserted between the source of moisture and the adjacent building structure. These membranes act as a barrier, preventing water from working its way into the walls and floors.

Integral Damp-Proofing

You can also damp-proof a building by mixing certain compounds into the concrete. These compounds can work in three different ways.

First, they can simply fill up most voids in the concrete, making it less porous. Alternatively, the compounds may possess integral water-repellent properties that they impart to the surrounding concrete. And lastly, the compounds can react with the concrete to produce water-resistant alkaline silicate.

Damp-Proofing Paints

As the name applies, damp-proofing paints are water-resistant paints that can be applied to various surfaces. They're incredibly effective against rain and condensation, and they're quite easy to apply. However, they don't work well when applied to structures under pressure.

Damp-Proof Sheeting

As opposed to damp-proof paints, damp-proof sheeting works wonderfully under pressure. It's basically a waterproof sheet installed above the ground to prevent the rising dampness from reaching the overlying concrete slabs.

Damp-Proofing Rods or Creams

Damp-proofing rods and creams are a silane/siloxane polymer with water-repellent qualities. They're mainly used to stop the capillary action of walls. To install them, you simply drill holes along a mortar course and fill them up with the damp-proofing substance.

Cavity Wall Construction

This method of damp-proofing prevents the passage of water from the outer skin wall to the main internal wall by making a space between the two walls and filling it with an insulating material. Accordingly, the water outside will be the only thing affected, and the internal structure will remain intact.

Common Materials Used in a Damp-Proof Course

Damp-proof course materials can be divided into four main groups: rigid, semi-rigid, flexible, and grouting.

The rigid materials include first-class bricks, cement concrete, stone, slate, etc. And the semi-rigid group includes materials like mastic asphalt.

Meanwhile, the grouting materials are usually made of cement slurry, polymers, or acrylic-based chemicals. As for the flexible materials, there are:

  • Plastic (polyethene) sheets
  • Hot bitumen
  • Metal sheets
  • Bituminous felts

What Is the Ideal Damp-Proof Course Like?

An ideal DPC material should be:

  • Completely water-resistant
  • Durable
  • Strong enough to withstand loads
  • Flexible enough to cover any surface without breaking
  • Easily and securely attached to any surface
  • Dimensionally stable
  • Free from deliquescent salts like chlorides, sulphates, and nitrates
  • Affordable and readily available
Damp to Walls & Floor

How Is DPC Treatment Applied to Buildings?

DPC treatment in buildings consists of many steps.

First off, there are the foundations. These are damp-proofed by installing foundation drains, RCC rafts, asphalt tanking, and of course, the damp-proofing material.

After that, you need to damp-proof the floors. Typically, this is done by spreading a thick layer of sand under the floor, followed by a damp-proof sheet or membrane.

The walls are next, where a damp-proofing material is applied to both the external and internal walls, about 15 cm above ground level. Once this is over, the roofs are the final step in the damp-proofing process to protect against any rain-induced water damage. 

Damp-Proofing Course Pros

Installing a damp-proof course in your building can help you in many different ways.

For one, it'll prevent all structural issues caused by dampness. So, no more wet rot or dry rot for you. No more crumbling plaster and ruined plaster walls, either.

As such, your building will stay intact for the longest time possible, requiring minimal maintenance now and then. In the long run, this will ensure the building keeps its value.

Additionally, damp-proofing prevents mould growth and its resultant musty odour. As such, indoor air quality will drastically improve, enhancing your health in the process.

Damp-Proofing Course Cons

Nothing is free of flaws, and that includes damp-proofing.

Its biggest flaw is that it can be a bit costly to install. Now, if you consider it an investment in your building, it won't seem like such a burden.

Still, it can be pricey, and sometimes it can develop cracks. This means you'll need to replace it at one point or another.

Nevertheless, this is a minor disadvantage, and the benefits far outweigh the drawbacks. So, don't hesitate to invest in damp-proofing your building.

How to Install a Damp-Proofing Course

Fortunately, it’s quite easy to install a damp-proof course. You just remove the water-contaminated plaster walls, then spread a thin layer of mortar on the original masonry or concrete.

Then, lay your DPC on the mortar and wait for it to bond. Make sure to level and smoothen the mortar so that the DPC won’t be damaged in the application process. After that, you overlay the DPC in the corners and roll joints to ensure a complete seal.

Now, a damp-proof course can be installed either vertically or horizontally. In both cases, though, the DPC should never be left exposed during the finishing work, or it’ll be damaged. So, once the DPC is fixed in place, you cover it with a render or plastic, and voila!

Where Should I Install a DPC?

A damp-proof course is usually installed in the lower parts of the walls to prevent the rising dampness. However, it can also be installed below floors, in basements, foundations, and roofs to ensure total water resistance.

How Much Does DPC Installation Cost?

The average cost for damp-proofing one metre of a wall is about £80. This usually comes up to £350 for a single wall. So, if you'll be treating all the walls in your house, expect your receipt to be in the thousands.

Now, if the exterior ground level is higher than the DPC level in your walls, this makes your DPC ineffective. As such, you'll need to pay £450 to £600 to lower your ground level, which means digging all around the house and laying a layer of gravel or concrete.

Conclusion

Installing a damp-proof course in your home is absolutely essential to maintain its condition. By stopping the passage of water to the building walls and floors, you can save your house from issues like rot, rust, mould, and collapse.

So, if you're seeing signs of dampness in your home, contact the nearest professional and have them take care of it as soon as possible. Yes, it'll cost a bit, but it'll be worth it in the end.

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