Sealing slurry – also referred to as mineral sealing slurry or slurry waterproofing – is a cement-bonded, usually polymer-modified coating for waterproofing mineral substrates against water, moisture, and capillary transport. It is used in building construction and civil engineering on tanks, basements, shafts, tunnels, basins, and foundations. In planning, construction, and deconstruction, understanding it is essential: the properties of the slurry influence both the durability of a structure and the choice of safe, low-vibration separation and demolition methods, for example with concrete pulverizers or rock and concrete splitters from Darda GmbH, especially in sensitive applications such as concrete demolition and special deconstruction or rock breakout and tunnel construction.
Definition: What is meant by sealing slurry
Sealing slurry is a mineral, hydraulically hardening waterproofing system applied to concrete, masonry, or render in one or more coats. It creates a capillary-breaking, watertight layer that—depending on the product—is rigid or flexible, effective on the positive side (water side) or the negative side (back side), and may have limited crack-bridging properties. Typical applications include waterproofing tanks and basins, earth-contacting components, plinths, and shafts, as well as the refurbishment of damp substrates. Bond is achieved through crystalline interlock and polymer film, water absorption is reduced, and resistance to hydrostatic pressure is improved.
Fields of application and interfaces in deconstruction and tunnel construction
In deconstruction, existing sealing slurry acts as an additional coating layer. It can influence surface hardness, friction at gripping edges, and the fracture line in concrete. In selective deconstruction—such as within the scope of strip-out and cutting—it must be decided whether to remove the slurry beforehand or to remove it together with the concrete cover zone in segments. In water-bearing areas, for example in shafts, tunnels, or basins, the slurry controls the surface moisture behavior, which affects dust suppression and the choice of mechanical separation. Low-vibration methods, such as controlled splitting with rock and concrete splitters or segmenting nibbling with concrete pulverizers, help protect water-sensitive neighboring structures, linings, or shotcreted inner shells in rock breakout and tunnel construction.
Practical example scenarios
- Deconstruction of drinking water tanks: sealing slurry on the positive side requires clean segment separation; concrete pulverizers can define component edges, steel shears cut exposed reinforcement.
- Basement refurbishment with negative-side waterproofing: for openings, the slurry is locally removed; for more extensive removal, hydraulic wedge splitters are used to initiate controlled cracks.
- Basin refurbishment in wastewater treatment plants: slurry with chemical exposure affects tool wear; combined strategy of mechanical removal and segment deconstruction with combination shears and Multi Cutters.
- Deconstruction of steel tanks with a mineral inner lining: segmentation of the tank with a tank cutter, followed by separating the inner lining as mineral coating waste.
Material types and properties
Mineral sealing slurries can be broadly divided into rigid and flexible systems. Rigid slurries (mineral, cement-rich) are watertight under pressure but only limitedly crack-bridging. Flexible slurries (polymer-modified, two-component) have higher elongation and better crack-bridging and are often used on the positive side of highly stressed components. Crystalline systems promote the formation of water-insoluble crystals in capillaries and act by blocking capillaries, which reduces the depth of water penetration.
Mechanical and building-physics performance parameters
- Adhesion tensile strength: essential for durable waterproofing; substrate preparation largely determines the values.
- Compressive strength and abrasion resistance: relevant under mechanical loads, e.g., in shafts or basins.
- Crack-bridging class: flexible systems achieve higher classes and are suitable where movement or thermal fluctuations occur.
- Coat thickness: system-dependent; multi-coat application improves tightness and error tolerance.
- Water vapor diffusion: usually vapor-permeable; residual moisture can escape, which benefits refurbishment.
Substrate preparation and application
The effectiveness of sealing slurry strongly depends on substrate bond. Required are sound, clean, roughened, and matt-damp surfaces. Cement laitance, sintered layers, old paints, and loose particles must be removed; edges and coves are formed constructively. Application is by brushing, troweling, or spraying in one or more coats, often wet-on-damp, with a defined waiting time between coats. Gentle curing prevents overly rapid drying and cracking.
Typical installation steps
- Preparation: cleaning, mechanical roughening, removing bond-breakers, pre-wetting to saturation (without water film).
- Detailing: coves, crack treatment, corner reinforcement; if necessary, placing a reinforcing fiber in the first coat.
- Application: brush on the first coat generously, the second coat crosswise; check coat thickness.
- Curing: protect from wind, sun, and frost; moist curing to support hydration.
- Quality assurance: pull-off tests and visual inspections, tightness tests depending on the component.
Testing, maintenance, and refurbishment
Quality assurance includes pull-off tests at test areas, visual checks for pores, blisters, defects, and tightness tests in tanks. In case of defects, measures range from local touch-ups to full-area renewal. For refurbishments, existing coatings are partially or fully removed depending on condition. If selective removal is uneconomical, the edge concrete zone is removed in segments. In concrete demolition and special deconstruction, concrete pulverizers are often used for defined edges and rock and concrete splitters for low-vibration separation; exposed reinforcement can be cut with steel shears. Hydraulic power packs supply the tools with the required power, especially in confined conditions during strip-out and cutting.
Deconstruction: removing sealing slurry
Mechanical methods such as blasting/peening, grinding, milling, and chiseling are available for removing sealing slurry. Dust and water management is crucial to avoid introducing fine dust and alkaline wash water. For thick, strongly bonded systems or when the concrete cover zone is also impaired, segment-wise separation of entire component areas is often technically cleaner than pure surface removal. Here, rock wedge splitters provide controlled crack initiation inside the component, while concrete pulverizers produce precise segment sizes. In mixed-material areas—e.g., embedded parts, steel profiles, pipelines—combination shears and Multi Cutters support fast separation. For steel tanks with a mineral internal lining, the shell is opened in sections with a tank cutter, and the coating is then handled as mineral construction waste.
Occupational safety and environment
- Dust and alkalinity control: extraction, misting, catch trays; protection against skin- and eye-irritating media.
- Water management: collect rinse and cleaning water and dispose of it properly; observe discharge permits.
- Noise and vibrations: in sensitive areas, prefer low-vibration methods such as splitting.
- Material flow management: collect coated concrete segments separately; documented separation facilitates recycling.
Planning, standards, and quality
For selecting and applying sealing slurry, recognized rules of technology and relevant standards must be considered depending on the project. In Germany, these include waterproofing standards for earth-contacting components, interiors, and tanks, as well as requirements for surface protection systems on concrete components. For deconstruction, general occupational and environmental protection requirements additionally apply. From a planning perspective, water pressure, crack patterns, crack width limitation, joint detailing, substrate moisture, temperature, and construction sequencing must be assessed. Careful documentation of substrate inspection, coat thicknesses, curing, and acceptances facilitates later deconstruction and refurbishment.
Terminology and practical classification
Sealing slurry differs from polymer-modified thick bituminous coatings and resin-based waterproofing through its mineral character, vapor permeability, and excellent bond to damp, mineral substrates. It is predestined where robust, mineral systems are required, for example on walls, slabs, and tanks. For later interventions—core drilling, openings, segment deconstruction—the layer sequence must be recorded. In practice, a staged approach has proven effective: local exposure of the slurry, assessment of the edge zone, and then either selective surface removal or segment-wise separation with concrete pulverizers and rock and concrete splitters. This approach supports clean cut edges, short shutdown times, and controlled construction logistics—especially in concrete demolition and special demolition as well as for special operations in water-bearing structures.