Tanking Slurry
What Is Tanking Slurry?
Tanking slurry is a cementitious waterproof coating designed to provide an impenetrable barrier against water and dampness in structures. Typically composed of Portland cement, graded aggregates, and chemical modifiers, it’s mixed with water to form a slurry. When applied to walls, floors, and other surfaces, it cures to form a hard, dense barrier, preventing the passage of water and moisture. This method is especially effective in below-ground waterproofing applications like basements, cellars, and tunnels. Tanking slurry can adhere to various substrates, including concrete, brick, and stone, making it a versatile solution for waterproofing both old and new buildings. It is favoured in situations where conventional damp proofing is not feasible or has failed, offering a reliable and durable option for tackling pervasive damp issues.


How Tanking Slurry Works
Tanking slurry works by creating a waterproof barrier that adheres to the substrate, preventing water from penetrating the surface. Upon application, its water-reactive chemicals enable it to penetrate the substrate’s pores, effectively sealing them against moisture ingress. As it dries and hardens, the slurry forms a dense, impermeable layer that locks out water. This layer is resistant not just to liquid water, but also to water vapour, making it an excellent choice for damp-proofing basements, cellars, and other moisture-prone areas. The effectiveness of tanking slurry lies in its ability to withstand external hydrostatic pressure, meaning it remains intact and functional even under conditions where water pressure is high, such as in below-ground level settings. This characteristic makes it a superior choice in areas where groundwater levels are high or where seasonal changes can increase water pressure against the structure.
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How to Apply Tanking Slurry
Applying tanking slurry requires careful preparation and execution. The surface must first be clean, sound, and free from any loose material, dust, or contaminants that could impair adhesion. If necessary, repair any large cracks or holes before application. Dampen the surface lightly before applying the slurry to ensure good adhesion and to prevent premature drying.
Mix the tanking slurry as per the manufacturer’s instructions until a uniform, lump-free consistency is achieved. Use a stiff brush, roller, or trowel to apply the slurry, covering all areas thoroughly. It’s crucial to apply the slurry evenly, with particular attention to corners and joins where walls meet floors. Apply in a minimum of two coats; the second coat should be applied perpendicular to the first to ensure full coverage. Each coat must be allowed to become ‘tacky-dry’ before the next is applied. After the final coat, ensure the area remains undisturbed while the slurry cures, forming a solid, watertight barrier.


Is Tanking Slurry Breathable?
The breathability of tanking slurry is a point of consideration, particularly in older buildings where moisture transfer is a part of the wall’s natural drying process. Traditional tanking slurry formulations are generally not breathable, creating a non-permeable barrier that blocks moisture transmission. This means that while they are excellent at preventing water ingress, they do not allow trapped moisture within the walls to escape, which can sometimes lead to issues in certain types of masonry or in structures with existing dampness problems.
However, advancements in technology have led to the development of some breathable tanking slurry products. These products allow for some degree of moisture vapour permeability, aiding in managing moisture levels within the structure while still providing an effective barrier against water ingress. It’s essential to choose the right product based on the specific needs and conditions of the building. For heritage properties or structures where moisture retention is a concern, consulting a specialist to choose a suitable breathable tanking solution is advisable.
Types of Damp Proofing


Plastering




Tanking Slurry for Concrete Floors
Tanking slurry is highly effective for waterproofing concrete floors, particularly in basements, cellars, and industrial spaces. To ensure maximum efficacy, the concrete surface must be properly prepared: clean, free of oil, grease, or loosely adhered materials. Any existing cracks or voids should be filled and levelled.
Begin by applying a primer if recommended by the slurry manufacturer. When applying tanking slurry to concrete floors, ensure the mix is consistent, free from lumps, and prepared according to the manufacturer’s guidelines. Using a stiff brush or roller, apply the first coat evenly, focusing on achieving a comprehensive cover, especially in joint areas between floors and walls. Allow the first coat to partially dry (check specific product instructions for exact timings) before applying the second coat, ideally at right angles to the first to cover any gaps.
A crucial aspect to consider when tanking concrete floors is the potential for hydrostatic pressure buildup. Ensure any drainage issues are addressed beforehand, as tanking slurry will block water escape routes, possibly leading to pressure buildup under the slab.


Tanking Slurry for Stone Walls
Tanking slurry is an excellent choice for waterproofing stone walls, often found in older buildings and basements. The irregularity and porosity of stone can pose a challenge, making thorough preparation and application vital. Start by cleaning the stone wall, removing any moss, mould, or loose material, and repair significant gaps or cracks.
When applying tanking slurry to stone walls, consider the slurry’s ability to penetrate the stone’s irregular surface. The first coat should be applied with a stiff brush, working the slurry well into the stone to ensure it enters all the pores and cavities. Stone walls, with their varied textures and shapes, might require a bit more material to achieve an even coverage.
Allow the first coat to dry until it’s firm but still tacky — the exact time may vary based on temperature and humidity. Apply the second coat perpendicular to the first to ensure all nooks and crannies are covered. Remember, the slurry must form a continuous, unbroken film over the wall to provide effective waterproofing. In environments with particularly high moisture, consider a third coat for extra protection.
Frequently Asked Questions
What is the main advantage of using tanking slurry?
Can tanking slurry be applied over paint or other finishes?
How long does tanking slurry take to dry?
Is tanking slurry suitable for DIY application, or should it be professionally applied?
Does tanking slurry work in high groundwater areas?
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