Put an end to damp walls! The ultimate guide to damp-proofing courses.
Moisture rising up through the masonry can be a nightmare for any homeowner. A professionally installed damp-proof course is often the only way to protect the structure of the building. In this article, you’ll learn all about the causes and solutions, and why choosing the right technique is crucial for long-term success.
Why do you need a damp-proof course at all?
The reason lies in physics: mineral building materials are porous and contain countless capillaries. These act like tiny suction tubes, drawing water upwards from the damp ground against the force of gravity. This ensures that moisture penetrates the masonry ‘of its own accord’ and rises within it.
Signs of damage: How can you spot the problem?
Rising damp is usually easy to spot. Typical signs include:
Visual defects: – Damp patches, – Dark discolouration, – Unpleasant water marks on the walls
Surface damage: – Flaking plaster, Salt efflorescence (white crusts), caused by crystallising salts
Health risks: The formation of mould, which is hazardous to health.
Indoor climate: A musty, damp smell in the affected rooms
Why do horizontal damp-proof courses fail?
In new builds, mechanical damp-proof courses, such as roofing felt (bitumen membranes), are typically installed. However, these have a limited lifespan.
Material fatigue: Over the decades, bitumen membranes become brittle and fragile. Building settlement or chemical processes in the ground can cause cracks through which moisture can rise unhindered.
Faulty repair attempts: Attempts to solve the problem using conventional chemical systems that rely on pore blockage (‘silicification’) often make matters worse. These systems do not form a tight ‘plug’, but merely constrict the capillaries.
This creates a physical vicious circle whereby, in narrower capillaries, water rises even higher due to physical forces. The result is that, after a few years, the damage simply reappears at an even greater height on the wall.
Why do newly installed horizontal water barriers often fail or prove defective from the outset?
The problem often lies in the method used. Many conventional systems rely on a process known as silicification, whereby pores are blocked.
The risk: These systems do not completely block the capillaries, but merely narrow them.
The fatal consequence? As water rises higher in narrower capillaries due to their physical properties, damage may occur at greater heights after a few years.
Application errors: Often, the borehole is not cleaned thoroughly. Drilling dust clogs the pore walls and prevents the sealing agent from penetrating deep enough into the building material.
Incorrect drill hole spacing or depth: If the borehole is drilled at the wrong angle, only 1/3 of the wall is penetrated, resulting in an incomplete sealing layer.
Why do horizontal waterproofing membranes fail?
In new builds, mechanical waterproofing layers, such as roofing felt (bitumen membranes), are usually installed. However, these have a limited lifespan.
Material fatigue: Over the decades, bitumen membranes become brittle and fragile. Building settlement or chemical processes in the ground can cause cracks through which moisture can rise unhindered.
Faulty repair attempts: Attempts to solve the problem using conventional chemical systems that rely on pore blockage (‘silicification’) often make matters worse. These systems do not form a tight ‘plug’, but merely constrict the capillaries.
This creates a vicious circle: in narrower capillaries, water rises even higher due to physical forces. The result is that, after a few years, the damage simply reappears at an even greater height on the wall.
How should a horizontal damp-proof course be installed correctly?
A modern chemical horizontal damp-proof course (using the injection method) can be installed in a few simple steps:
Preparation: Damaged plaster is removed over a wide area (approximately 80 cm above the moisture line), and joints are repaired where necessary.
Drilling: Drill holes are set in a grid or in a row. The depth corresponds to the wall thickness minus approximately 20 mm. The grid pattern of the drill holes depends on the chosen injection method.
Cleaning (essential!): Simply blowing out the holes is not enough. The holes should be cleaned with cylindrical wire brushes to clean the pores and and allow the active ingredient to penetrate.
Injection: Depending on the extent of moisture penetration, apply a liquid concentrate such as HydroBloc Si 709 (with pressure injection for water content >50%) or a cream such as HydroBloc Diffusion 715 (without pressure).
Non-pressurised injection of HydroBloc SI 709 using the drip container
Sealing: The holes are permanently sealed with an expansion mortar such as SealFix 930.
When is a horizontal damp-proof course not suitable?
It is important to understand that horizontal damp-proof courses are purely moisture barriers. They offer no protection against rising damp caused by high groundwater levels or standing water. Additional waterproofing measures are therefore required in such cases.
Why ARCAN products offer a permanent solution
Unlike other products, ARCAN does not simply plug the leak; it achieves water-repellency by interrupting capillary suction.
Chemical bonding: Products such as HydroBloc Diffusion 715 react with the structure of the building material and become virtually indissoluble when bonded to it.
Mode of action: Rather than merely ‘plugging’ the hole, the pore walls are made water-repellent. Capillary action is deactivated, meaning that water can no longer wet the surface, and water transport is permanently halted.
Extreme situations: HydroBloc Si 709, a reactive siloxane concentrate, has been specially developed for use in water-saturated building materials where conventional silicone- or silane-based agents are ineffective or unsuitable.
From damp to very wet: The reactive siloxane products in the HydroBloc range are suitable for all degrees of moisture penetration.
Certified quality: The systems are tested and approved in accordance with the strict WTA guidelines, guaranteeing the highest technological standards.
COMING SOON: You can find additional products to help you achieve a smooth renovation in our article. The Perfect Finish.
