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Cementitious Basement Tanking: Type A Waterproofing Explained

waterproofing basement and foundationsWith space in the capital being at such a high premium, it makes sense that so many homeowners are now looking underground to find additional space. When it comes to basement conversions, though, one of the most important factors to consider is water. Waterproofing and an effective Damp Proofing Course (DPC) are essential ways to keep the above-ground areas of your property safe, but for basements, the constant presence of groundwater beyond the walls needs to be taken care of in order to ensure your underground space remains dry and damp-free.

Basement tanking offers an effective, efficient way to guarantee that your basement is fully waterproofed - and this is also a service that Garratt’s Damp & Timber excel in. Our expert team can employ one of two basement tanking techniques - Type A Waterproofing or Type C Waterproofing - and the following outline should give you a guide as to what Type A Waterproofing (Cementitious Tanking) entails.

However, if you are planning a basement conversion or renovation project, we would always recommend enlisting the help of a professional such as ourselves to ensure the most suitable basement tanking method is utilised and work is carried out to the highest possible standard.

Step One - Survey and Questions

The team of specialist surveyors here at Garratt’s Damp & Timber will examine your basement to determine the kind of materials and construction that was previously used. We will also discuss with you the long term goals of what you want to do with your basement once it is converted.

All of this information will inform us on the techniques, tools, and types of waterproofing materials that will work best for your specific situation.


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    Step Two - Stripping and Clearing

    For Type A Waterproofing, the next step is all about careful preparation. Preparing the surface prior to application of any Type A Waterproofing system is key. The chosen system will only be as good as the substrate. Once the walls are prepared exposing the outer most materials, which in most cases is brickwork and concrete. Our team would take out the mortar joints to allow for maximum suction of our system.

    If a non-specialist performs this type of works, serious structural problems could be in store for the property as a whole. Any damage sustained to the structural walls and/or footings could potentially compromise the structural integrity of the entire building. As a result, it’s essential to employ only certified experts who are highly familiar with this type of work.

    Garratt's Damp and Timber have over a decade and a half of tried and tested experience with basement tanking, meaning that you be more than confident in the service we offer.

    We often encounter painted brickwork in basements; such a finish requires either scabbling or grit blasting to remove the paint. This will permit good contact for any splatter coats or render. Leaving paint in place often results in the treatment de-bonding from the walls over time.

    Step Three - Waterproofing

    The final step is to install the barrier system that will complete the process. Cementitious tanking involves surrounding the entire basement with a waterproof barrier essentially creating a tank to prevent groundwater from entering the internal areas of the basement.

    This barrier can come in a range of different options, from waterproof renders to specialised slurries and epoxy resins. We do not believe in one size fits all solutions, so you can be sure that the product we recommend for your basement is based on expert knowledge for the project you want to undertake, as well as the materials and construction of your existing basement space.

    Once the waterproof layer is in place, you will be free to design and decorate your new basement conversion as you wish.

    The process of application after the previously mentioned preparation works is as follows:

    • Plug/water stop any leaking water/water ingress
    • Apply a splatter coat to all surfaces
    • Apply multiple coats of waterproof render
    • Install a fillet seal to the vulnerable floor/wall join areas of the basement. This will assure a smoother transition of groundwater from walls to floor
    • Apply a cementitious slurry/screed or epoxy resin to the floor

    Why Choose Cementitious Basement Tanking?

    Type A Waterproofing is the standard option for most basements. Generally speaking, it is the simplest and easiest to install basement tanking system. In London, this type of waterproofing is especially valuable due to the higher than average level of groundwater, caused by the large number of densely clustered buildings in the capital. With so many foundations in a relatively small area, the surrounding groundwater gets displaced and rises. This makes simply blocking the groundwater with a cementitious barrier often the ideal basement tanking solution.

    As a general rule, we would usually recommend Type C Waterproofing when the outer walls of a basement are either listed or expecting high volumes of groundwater. Step two outlined above may be a problem, even for experienced basement engineers. For those situations, alternatives like Type C Waterproofing are preferred.

    If you are considering basement tanking to give your London home a little extra space, contact Garratt’s Damp & Timber to learn more about waterproofing and how we can help you get the most out of your underground space.

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