Type A Basement Tanking Specialists

Basements and cellars are often forgotten about, but there are techniques to turn damp and leaky below ground areas into habitable living spaces. This can add more storage space to your property, while increasing it’s value.

Basement tanking is one of the most common ways to waterproof a below ground space, by creating a watertight barrier between the surrounding damp ground and the internal space. Moisture can pass through the ground and into the brickwork of your basement, which then causes damp inside. If you create a waterproof barrier, this can help prevent this moisture ingress.

For habitable living, basement tanking is often used in conjunction with another type of waterproofing system, like cavity drain membrane waterproofing, as per guidelines set out in the British Standard 8102, the industry standard for below ground waterproofing. If you are considering converting your basement or cellar then get in touch with Rentokil Property Care, we have a number of local CSSW qualified surveyors who can provide advice around basement tanking and other forms of waterproofing, to help unlock the potential of your below ground space.

We can design waterproofing systems to British Standard 8102, and we have been carrying out basement conversions up and down the country for decades, from our network of local branches.

Basement tanking is a method of waterproofing by applying a waterproofing coating or membrane to the external or internal walls and floor of a basement which helps create a watertight barrier. Known as Type A waterproofing, once the tanking application is completed it will prevent water seepage from entering the internal space, as well as hygroscopic salts migrating through into the internal surfaces. 

By covering floors and walls the barrier created forms a ‘tank’ around the internal space, preventing moisture from entering. This means the internal space will be kept dry, making it a suitable solution for properties located in areas with high water tables or saturated ground. Basement tanking is a versatile way to create a watertight seal, and depending on the property in question a Type A tanking solution can be applied internally or externally, either in the form of a slurry or tanking membranes.

The most common way to tank an existing basement is to use a tanking slurry to form a waterproof barrier, which typically consists of a cementitious product which is directly applied onto the walls and floors. The slurry will bond to the surface and cure, creating a watertight barrier that prevents water ingress. This is sometimes known as cementitious tanking.

Tanking can be applied on external walls if there is sufficient access, making it more commonly used for new build properties in conjunction with pre-applied fully bonded membranes installed below floor slabs. For remedial basement conversions tanking slurry is applied on internal walls, with the newly applied barrier holding back the pressure of ingressing water.

Type A tanking membranes can also be used to create a waterproof barrier and are often used on new build properties. Pre-applied sheet membranes are used when waterproofing the new floor slab. These are installed to be continuous with the waterproof tanking applied to the walls.

Geodrain protection membrane can be used against external tanking to protect the newly installed tanking slurry when the structure is buried.

Waterproof membranes applied to walls and floors are more commonly part of a Type C cavity drainage membrane system, which are often used in conjunction with a Type A system. When Type A and Type C are combined, it allows the designed system to meet BS8102 specification for habitable living spaces, removing further risk from water ingress.

Increasing habitable living space by waterproofing a damp basement is an increasingly popular decision across the UK, especially in cities where land is at a premium. That said, in order to guarantee a dry environment there are numerous factors that need to be considered.

Increased ventilation may be required to prevent condensation, particularly if the tanked area is for habitation.

Any space that is below ground level is susceptible to moisture ingress from lateral penetrating damp through walls and floors, but also from flooding, burst water mains, run off and surface water from above. Topography, geology and water tables must be considered when designing a waterproofing system, as the design must take into account any new risks in the future to remove the risk of flooding or water ingress.

Because waterproofing is a complex process that requires knowledge and experience to get right - a qualified surveyor should always be used. For below ground waterproofing a CSSW (Certificated Surveyor in Structural Waterproofing) qualified surveyor will design a system to the industry standard for waterproofing, British Standard 8102. This will mean that the surveyor has specified a design fit for purpose, before trained and expert technicians can install a system fit for purpose and with high levels of precision.

The first step is to address and prevent water seepage where walls and floors will be prepared in order for an application of tanking slurry to be applied. It’s essential to use the correct products and great care must always be taken when applying slurries in order to maintain a continuous barrier, especially in the weakest areas such as wall floor joints. If the wrong products are used, or installed incorrectly it can lead to basement tanking failure, causing moisture to penetrate inside.

This might not be noticed straight away and could lead to damage of newly installed plaster, flooring, stored goods and furnishings. This is why it is so important to use a reputable company who you can trust to get it right the first time.

Waterproof tanking can be used on walls and floors of buildings if they are below ground level to help prevent moisture ingress. The type of tanking method will depend on the existing construction and access, and the most common way to tank an existing wall is to apply a cementitious render internally. 

It is very important when tanking to understand if the existing wall has the sufficient strength to resist the loading by water pressure on the surface once installed. While structural engineers will typically factor in this when designing a new build below ground space, this may not happen if you are applying tanking to an existing building.

Once you are confident that the wall can sustain the increased load from water pressure, the surfaces of the wall must be prepared for tanking slurry to bond correctly, meaning that existing renders of plaster must be removed, and any damaged mortar is repaired.

Newly applied tanking slurry may take 24 to 48 hours to fully cure, while in certain sections you may notice the slurry appear to ‘sweat,’ this is a normal part of the drying process.

Once the tanking has fully dried and cured it can then be plastered ready for decoration. A skim coat can be applied directly to the tanking surface, although care must be taken not to damage or break the waterproof barrier in any way. If the coating is penetrated it could lead to moisture ingress into the internal space.

Waterproofing is an umbrella term used for all systems and methods of keeping out water ingress typically from structures that are below ground level, or below the damp proof course. These are categorised as Type A (barrier protection systems) where slurry or damp proof membranes are applied to the walls - known as tanking. Type B or ‘integrated systems’ where the waterproofing is built into the structure itself. Or Type C, which involves the installation of a ‘cavity drainage system’. These types of waterproofing systems are defined in British Standard 8102.

Tanking is therefore a category within waterproofing that refers explicitly to the use of either cementitious slurry or membrane barrier protection.

The best waterproofing solution is totally dependent on the type of structure in question, the location of the property, size of the below ground space, topography, flood risk and water tables. While the end use of some basements may allow for moisture seepage, generally speaking when converting a basement for habitable living it is required to use a combination of waterproofing systems to help reduce risk.

For guaranteed protection for habitable space it is highly recommended to use a mix of Type A, Type B or Type C systems that are in line with industry standards defined in British Standard 8102.

A CSSW qualified surveyor will be able to provide advice and a waterproofing solution that is right for your property, designed to BS8102. This will be detailed in a survey report, along with a clear explanation of what will be carried out, from start to finish. 

The costs for basement tanking will depend on the size of the space involved, the condition and extent of damage to existing below ground walls and the type of tanking required. A waterproofing survey must first be carried out to fully understand the requirements needed to correctly install a Type A basement tanking system in your property.

If you wish to go ahead with a waterproofing survey by Rentokil Property Care, our CSSW qualified surveyor will carry out a thorough survey of the property, including internal and external checks, and will then provide you with advice, solutions and a quote for any waterproofing required dependant on your proposed end use of the space in question.

Incorrectly installed basement tanking that leads to a system failure can cause damp problems, mould growth, fungal decay and even structural issues if hydrostatic pressure is not taken into account. This is why it is so important to use a reputable company for any below ground waterproofing.

Tanking your own basement or cellar is possible, but is not recommended unless you are experienced in below ground waterproofing, as if done incorrectly can lead to moisture ingress, structural issues and even fungal decay. The correct products must be used and installed correctly, while improvements to ventilation should also be considered.

Many older properties in city centres - those which people often wish to convert into habitable basements - often have shallow foundations and if these are disturbed can lead to movement in supporting walls. Walls may be deteriorated and require structural repairs before tanking is carried out.

Cellars and basements are vulnerable to vibrations from nearby roads and extreme hydrostatic pressure from water in surrounding ground. When tanking systems are installed on existing walls and floors, it can result in forces pushing inwards by ground water pressure, leading to cracks and leaking of the tanking system, and even structural damage to walls and floors.

If a system fails it will cause damage to stored goods, furniture and any installed flooring or plaster, which may need to be discarded or replaced.

A CSSW qualified surveyor will provide advice and solutions for these factors when designing a Type A tanking system. It is advisable to consult with a CSSW qualified surveyor before attempting to waterproof your basement or cellar.

• Rentokil Property Care have CSSW qualified surveyors working out of our network of branches across the UK, meaning we have a waterproofing expert local to you. We can work with homeowners, architects, contractors and commercial partners to design a basement waterproofing system to suit your project.

• Our trained technicians will install the Type A tanking system using the correctly specified products, installed as intended. One mistake can lead to system failure, so it's important that the installation process is carried out by trained and experienced professionals.

• Rentokil Property Care has a thorough quality assurance process, with regular checks throughout the installation process. The CSSW qualified surveyor who designed the system will carry out site visits and provide a final sign off process in order to ensure our exceptionally high standards are met.

• Rentokil Property Care are approved installers of Delta, Koster, Newton and Safeguard waterproofing products, with both in house and onsite training carried out to qualify as a trusted partner. We use waterproofing products that undergo an extensive testing process by the manufacturers to attain BBA/BDA certification.

• A Rentokil Property Care basement system designed to BS8102 standard comes with a 10-year guarantee - giving you long term protection and peace of mind.

• We are proud members of the Property Care Association (PCA). When you work with us you can be assured that you’re getting professional and honest advice, and treatments following the industry best practice.

• Our damp proofing, structural repairs and timber treatments are rated ‘Excellent’ with over 1,000 reviews from our customers - showcasing our professionalism.

• We are endorsed by Which? Trusted Trader - meaning our customer service and workmanship has passed the rigorous trading standards assessments.