How to tank a celler

How to Tank a Cellar? The Comprehensive Guide to Cellar Tanking

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Key Takeaways:

  • Understanding Cellar Tanking: Cellar tanking is a process of waterproofing or damp-proofing a cellar or basement to prevent water penetration. The term ‘tanking’ involves creating a tank-like waterproof seal around the cellar using a specially designed mixture called tanking slurry.
  • Importance and Benefits of Waterproofing: Waterproofing a cellar is a crucial investment with numerous benefits, including safeguarding structural integrity, preventing mould and mildew, increasing property value, creating extra living space, enhancing energy efficiency, deterring pests, and preserving the overall investment in the property.
  • Tanking Cellar Walls: Successful cellar tanking relies on proper preparation, including the removal of loose paint or plaster from walls and addressing salt contamination. It is crucial to check for active water seepage before applying tanking.

In an ideal world, every home would be perfect, free from issues like damp or leakage. Unfortunately, we don’t live in a perfect world. This is especially true for those of us with cellars or basements.

Given their location beneath ground level, these areas are prone to damp and water penetration, which can lead to various structural and health issues if not addressed properly.

One popular method for preventing such problems is ‘Cellar Tanking’. It is a widely used technique in the world of construction and home improvement, but not everyone is aware of what it entails, how it works, and why it’s important.

In this article, we’ll provide a comprehensive guide to cellar tanking, explaining everything from the science behind tanking slurry to the practical steps of waterproofing your cellar. By the end, you’ll have a good understanding of the process, its costs, and even some alternative methods.

>> Related Reading: Tanking VS Waterproofing – What Is The Difference?

What is Cellar Tanking?

Cellar tanking refers to the process of waterproofing or damp-proofing a cellar or basement. This technique involves applying a waterproof coating (often called a tanking slurry) to the walls and floor of a cellar to prevent water penetration.

The term ‘tanking’ refers to creating a ‘tank-like’ waterproof seal around your cellar or basement.

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How does tanking slurry work?

resist water pressure

Tanking slurry, the most common material used in cellar tanking is a specially designed mixture of cement and water-resistant additives. When applied to the surface of the cellar, it forms a barrier that water cannot penetrate.

The effectiveness of tanking slurry lies in its composition. The additives react with the moisture present in the substrate, creating insoluble crystals that block the pores of the cement, preventing water ingress. Over time, this reaction continues to improve the waterproofing properties of the slurry, creating a durable, long-lasting barrier against water.

Why Waterproof A Cellar

Waterproofing a cellar is a significant investment that comes with a variety of benefits. Here are eight compelling reasons why you should consider waterproofing your cellar:

  • Structural Integrity: Over time, water seepage can seriously compromise the structural integrity of your house. It can weaken the foundation, cause cracks in the walls, and even lead to a complete collapse in severe cases. Waterproofing your cellar can help protect the structural integrity of your home.
  • Preventing Mould and Mildew: Damp and humid conditions are the perfect breeding ground for mould and mildew. These fungi can cause a host of health problems, including allergies, asthma, and other respiratory issues. Waterproofing can prevent these conditions from developing in your cellar, promoting a healthier home environment.
  • Increased Property Value: A waterproofed cellar can significantly increase your property value as tanking slurry blocks water. Potential buyers will appreciate the extra usable space and the peace of mind that comes with knowing the house is protected against water damage.
  • Extra Living Space: A damp, musty cellar isn’t good for much. But a dry, waterproofed cellar can provide additional living space, whether that be a home office, a guest bedroom, a home gym, or a playroom for the kids.
  • Energy Efficiency: Damp in a cellar can lead to higher humidity levels in the rest of the house, which can make your HVAC system work harder to maintain a comfortable temperature, leading to higher energy bills. A dry, waterproofed cellar helps to improve the overall energy efficiency of your home.
  • Preventing Pests: Damp environments can attract a variety of pests, including insects and rodents. By keeping your cellar dry, you can help deter these unwelcome guests.
  • Preserving Your Investment: For most people, their home is their biggest investment. Waterproofing your cellar is a way of preserving that investment and preventing potentially costly repairs down the line.

Tanking Cellar Walls

tanking exposed


Proper preparation is the key to successful cellar tanking. First, remove any loose or flaking paint, plaster, or render from the walls. This can be done using a wire brush or a mechanical chipping hammer.

Next, check for any signs of salt contamination. These can appear as white, powdery deposits on the wall. If these are present, they must be removed, as they can prevent the tanking slurry from adhering properly.

Check for Seepage

Before proceeding with the tanking, it’s essential to check for any active water seepage. If water is actively entering the cellar, this issue needs to be addressed before the tanking can be applied.

This may involve repairing cracks in the walls or floor or installing a land drain to redirect water away from the property.

Wall floor junction or fillet joint

The wall-floor junction, or fillet joint, is a critical part of the tanking process. This is where the wall meets the floor, and it’s a common point of water ingress. Therefore, it must be treated with special care during the tanking process.

How to create a wall floor junction or fillet joint

To create a fillet joint, mix the tanking slurry with sand to create a thicker mixture. Apply this mixture in a smooth curve at the point where the wall meets the floor, creating a continuous barrier that prevents water from seeping through the joint.

Make sure to apply the mixture at least 2 inches (5 cm) up the wall and 2 inches onto the floor to ensure a solid, watertight bond.

Mixing the Tanking Slurry

Follow the manufacturer’s instructions for mixing the tanking slurry. Generally, this involves gradually adding the slurry powder to clean water while mixing until a smooth, lump-free consistency is achieved. The mixture should be thick but still easily spreadable, similar to the consistency of thick paint.

Applying the Cellar Tanking

treat damp walls

Using a brush or roller, apply the tanking slurry to the prepared cellar walls. Start at the bottom and work your way up, ensuring a consistent, even layer is applied. For the best results, apply two coats, allowing the first coat to become touch-dry (usually 3-4 hours) before applying the second coat.

Ensure the slurry is applied up to and over the fillet joint to create a seamless, continuous barrier against water ingress. Don’t forget to cover any protrusions or service pipes as well.

Tanking a Cellar Floor

Once the walls have been treated, it’s time to focus on the floor. Apply the tanking slurry to the floor in a similar manner to the walls, ensuring an even, consistent layer. Apply a second coat if necessary, allowing the first coat to dry before proceeding.

For added protection, consider installing a damp proof membrane on top of the tanked floor, followed by a screed or floor finish of your choice.

What Is The Cost Of Tanking A Cellar

The cost of tanking a cellar varies depending on factors such as the size of the cellar, the complexity of the project, and whether you choose to DIY or hire a professional. As a rough estimate, materials for a DIY project can cost between $5 and $15 per square foot.

Professional installation, on the other hand, can cost anywhere from $50 to $100 per square foot or more, depending on the contractor and the level of service provided.

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What Other Ways Can You Waterproof A Cellar

tanking slurry cures

While cellar tanking is indeed an effective method for waterproofing a basement or cellar, it’s not the only solution. Here are some other methods you might consider, each with its own advantages and disadvantages:

1. Cavity Drain Membrane

A cavity drain membrane is a type of basement waterproofing that uses a studded membrane on the damp walls and floor of the basement or cellar. These studs create a gap between the wall and the membrane, forming a cavity. This cavity allows water to flow down to a cavity drainage system that runs around the perimeter of the floor.

Water entering the basement is controlled and directed to a suitable drainage point, usually a sump pump. The sump pump then expels the water from the property, keeping the cellar dry.

Advantages of this method include the fact that it can be installed with minimal preparation and it’s less likely to be damaged by minor movements in the building structure. However, it does require a reliable sump pump system to remove the water, and this system must be maintained regularly to ensure it remains functional.

2. Exterior Waterproofing

Exterior waterproofing involves applying a waterproof coating or membrane to the outside of the foundation walls. This is typically done during the construction of the house but can be done later if necessary.

The process involves excavating the earth around the outside of the foundation, cleaning and preparing the porous cellar walls, and then applying the waterproof coating. A drainage mat with channels may also be installed against the wall to help divert water down to a cavity drain system at the base of the wall.

Exterior waterproofing is highly effective, as it prevents water from ever reaching the foundation walls. However, it’s also the most disruptive and expensive method, as it involves excavation around the house. It’s also not a practical solution for houses in close proximity to each other.

3. Interior Drainage Systems

Interior drainage systems function similarly to the cavity drain membrane system but are installed inside the cellar or basement. A channel is installed at the base of the walls, running around the perimeter of the floor.

Water entering the basement is captured by the channel and directed to a sump pump, which expels the water from the building. An interior drainage system can be installed with minimal disruption and doesn’t require any excavation outside the house.

However, like the cavity drain membrane system, it relies on a sump pump to remove the water, and this pump must be maintained to ensure it remains operational.

4. Sump Pumps

It’s a pump installed in a basement or cellar to help remove any water that has accumulated. The sump pump is installed in a specially constructed sump pit at the lowest point of the basement or cellar.

Water stream into the sump pit either through drains or naturally through the soil, and the sump pump pumps the water away from the house to a place where it can drain away naturally, such as a municipal storm drain or a dry well.

While sump pumps are an effective solution for managing water ingress, they are not a standalone solution and are usually used in conjunction with other methods, like a cavity drain membrane or an interior drainage system.

Remember, each property is unique and what works best will depend on factors such as the building’s structure, the nature of the soil, and the extent of the water ingress problem. It’s always a good idea to seek professional advice before deciding on the best solution for your property.

Final Thoughts

Waterproofing your cellar is a wise investment that can protect your home, increase its value, and even expand your living space.

It is a complex process, and while it can be done DIY for smaller projects, it is recommended to engage professionals for comprehensive waterproofing solutions, especially when dealing with significant water intrusion issues.

Remember, prevention is always better than cure. Regular maintenance and early detection of potential problems can save you from costly repairs in the future. Waterproofing your cellar is not merely about keeping it dry; it is about ensuring the structural integrity of your house, protecting your investment, and creating a healthier living environment.

How to Tank a Cellar – Frequently Asked Questions

  • What is the best way to tank a cellar?

    The best way to tank a cellar largely depends on the specific needs of your property, including the degree of damp or water ingress, the type of soil surrounding your property, and your intended use for the space. In general, applying a waterproof tanking slurry to the walls and floor of the cellar is a commonly used and effective method.

    However, for severe cases of water ingress, a cavity drain membrane system with a sump pump might be necessary. Consulting a professional can help you determine the best approach for your particular situation.

  • What is the method of basement tanking?

    Basement or cellar tanking involves applying a waterproof barrier (often called a tanking slurry) to the interior walls and floor of the basement. The process starts with preparing the surfaces by removing any loose or flaking material and checking for any active leaks.

    Then a fillet joint is created where the wall meets the floor to prevent water ingress at this common weak point. The tanking slurry is then mixed and applied to the walls and floor, with special attention paid to the fillet joint and any other potential weak points.

  • Will tanking a cellar stop flooding?

    Tanking a cellar can significantly reduce the risk of flooding by preventing water ingress through the walls and floor. However, it’s important to note that tanking cannot prevent flooding caused by issues like rising groundwater levels or severe weather events.

    In these cases, a more comprehensive waterproofing system, such as a cavity drain membrane system with a sump pump, might be necessary.

  • How do you waterproof a cellar in the UK?

    The process for waterproofing a cellar in the UK is generally the same as in other parts of the world. It starts with assessing the extent of the damp or water ingress and then choosing the appropriate waterproofing method. This could involve tanking the cellar with a waterproof slurry, installing a cavity drain membrane system, or a combination of both.

    If water ingress is severe, exterior waterproofing might also be considered. However, this can be disruptive and expensive, and it’s not suitable for all properties. As with any major home improvement project, it’s recommended to consult with a professional before proceeding.

Picture of Jake Fitzgerald - Damp Surveyor

Jake Fitzgerald - Damp Surveyor

Surveyor of Timber & Dampness in Buildings (CSTDB) & ( MRICS ) Chartered Quantity Surveyor

Jake is a qualified chartered quantity surveyor and experienced damp specialist with a unique skill set in thermal imaging. With a focus on effective solutions, Jake combines his expertise in quantity surveying and thermal imaging to accurately assess and address damp-related issues. He utilises advanced technology to identify hidden moisture sources and develop targeted strategies, ensuring comprehensive and cost-effective solutions for his clients. With a commitment to open communication and client satisfaction, Jake delivers cutting-edge solutions that tackle damp challenges head-on.

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