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Cementitious Tanking Slurry

Explains what a cementitious tanking slurry is as a material, why a rigid bonded coating and a structure that moves are an uneasy combination, and why below-ground work belongs with a specialist.

Typical role:Moisture and air controlSubstrate and base
Commonly met in:Foundations and groundworksInternal walls and ceilingsWet areas

Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.

Overview

What cementitious tanking slurry is

A cementitious tanking slurry is a cement-based coating supplied as a powder, or as a powder with a separate liquid component, and mixed on site to a brushable or trowellable consistency. It is applied to masonry or concrete and sets as a rigid mineral coating bonded directly to the surface beneath it.

The bond to the substrate is the whole mechanism. Unlike a sheet membrane, which is a separate layer laid against a surface, this material becomes part of that surface. That gives close contact and no laps to fail, and it also means that whatever happens to the substrate happens to the coating: a rigid coating bonded to a structure that cracks or moves will crack or debond along with it.

That characteristic is why it is discussed as one element of a designed scheme rather than as a waterproofing answer in itself. Substrate preparation, structural condition, movement, water pressure, drainage and what happens at every junction, penetration and termination all shape the outcome, and below-ground waterproofing in particular is a specialist design discipline. Some products are formulated to be more flexible than others, and the manufacturer's own description is what tells them apart.

Terminology

Common names and aliases

These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.

  • Tanking slurry
  • Cementitious tanking
  • Cementitious slurry coating

Applications

Common applications

Where this material is typically encountered. A typical application is not a statement that it suits your project.

  • Coatings applied to masonry or concrete as one element of a scheme designed by a specialist.
  • Surfaces prepared and coated as part of remedial work specified after professional investigation.
  • Backgrounds treated before other finishes are applied, where the designer has required that step.
  • Situations where a bonded mineral coating suits the geometry better than a separate sheet layer.
  • Coatings used together with drainage and other measures that form part of a wider designed scheme.

Consideration

Where it is commonly considered

  • Where a suitably qualified specialist has designed a scheme and identified this material as one part of it.
  • Where the substrate is sound, mineral and can be prepared exactly as the manufacturer requires.
  • Where a bonded coating suits the geometry of the structure better than a separate sheet layer would.
  • Where the structural condition has been assessed and any movement is understood in advance.
  • Where the scheme sets out what happens at every junction, penetration and termination.

Professional review

Where additional professional review is especially important

These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.

  • Anywhere below ground, unless a suitably qualified waterproofing specialist has designed the scheme.
  • On substrates that are cracked, moving, friable, contaminated or otherwise unsound.
  • On backgrounds the manufacturer excludes, including some boards, coatings and non-mineral surfaces.
  • As a response to observed damp, which needs professional investigation of the cause beforehand.
  • Where water pressure, ground conditions and drainage have not been assessed by a specialist.

Properties

Key properties to discuss

Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.

Substrate dependency
The coating works by bonding to the surface beneath it, so substrate soundness, cleanliness and preparation decide the outcome. A coating applied over a poor background inherits every problem that background has.
Moisture behaviour
It is used within schemes intended to manage water, but no coating makes a structure dry on its own. Outcomes depend on the designed scheme, the drainage, the junctions, the terminations and the workmanship together.
Installation dependency
Mixing, preparation and application are governed entirely by the manufacturer's system documentation, and this is not work that should be approached from general guidance of any kind.
Repairability
Because the coating is bonded and rigid, local repair means cutting back to sound material and re-establishing continuity, which is specialist work rather than a patching exercise.
Surface wear
The set surface is mineral and hard, but it is a coating rather than a wearing surface, and whatever goes over it forms part of the same designed scheme.
Appearance
It leaves a mineral coating, usually grey, with a texture that reflects how it was applied. Whether other finishes can be applied over it is a manufacturer's compatibility question.
Documentation
System documentation matters more here than for most materials, because these products are normally part of a defined system with its own primers, fillets, accessories and stated conditions of use.

Exposure

Exposure and environmental conditions

  • Is the element below ground, at ground level, or above it, since these are very different situations?
  • What do the site investigations say about groundwater and drainage around this structure?
  • Is water under pressure part of the picture here, which is a specialist question in its own right?
  • What is the internal environment of the space, including its ventilation and how it will be used?
  • Has anything changed outside the building, such as ground levels, drainage or paving?

Assembly

Substrate and system dependencies

What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.

  • The coating is only ever as sound as the substrate it has been bonded to.
  • Cracks and movement in the structure will be reflected directly in a rigid bonded coating.
  • Junctions between wall and floor, and around penetrations, are where schemes are made or lost.
  • Preparation requirements, including any primer or bonding treatment, come from the manufacturer.
  • Whatever is applied over the coating afterwards has to be compatible with it and with the scheme.

Appearance

Appearance and finish considerations

  • The finished surface is a mineral coating whose texture reflects the application method used.
  • Whether plaster, render, tiling or paint can go over it is a manufacturer's compatibility matter.
  • Colour variation between mixes and between batches is normal in cement-based materials.
  • It is usually covered by a later finish, so its own appearance is rarely the point of the work.
  • Any subsequent finish adds a further compatibility question to the scheme as a whole.

Durability

Durability questions

Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.

  • What is the structural condition of the element being coated, and who has assessed it?
  • Is movement expected in this structure, and what does that mean for a rigid bonded coating?
  • How is the coating protected from damage by following trades and by later occupation?
  • What does this scheme rely on besides the coating itself to achieve its intent?
  • Who is monitoring the space after completion, and what would they be looking for?

Upkeep

Maintenance and repair considerations

  • Who investigates if dampness appears in the space after the work has been completed?
  • Is there a record of the system used, including its primers and accessories?
  • Would any repair mean removing the finishes that were applied over the coating?
  • Is there maintenance the scheme depends on, such as drainage or pumping arrangements?
  • Who holds responsibility for the scheme as a whole rather than for individual products within it?

Installation

Installation dependencies

What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.

  • Substrate preparation is the largest single variable and is defined by the manufacturer.
  • Mixing and application follow the manufacturer's system documentation rather than general practice.
  • Site conditions during application and setting are governed by that same documentation.
  • Junctions, penetrations and terminations are detailed by the specialist designing the scheme.
  • Sequencing with structural work, services and finishes determines whether the coating stays intact.

Documentation

Documentation to request

Ask for these in writing, for the specific product being proposed, and keep them with the project record.

  • The full system documentation from the manufacturer rather than a single product data sheet.
  • The specialist's design for the scheme, including junctions, penetrations and terminations.
  • Substrate preparation requirements and any primer or bonding coat the system calls for.
  • Compatibility information for whatever finish is going to be applied over the coating.
  • Records of the structural and ground assessments the scheme has been built on.

Conversations

Questions for qualified professionals

Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.

  • Who is the suitably qualified specialist designing this waterproofing scheme?
  • What does the scheme consist of besides this coating, and how do those parts work together?
  • What is the structural condition of the substrate, and has movement been assessed?
  • How are wall-to-floor junctions, penetrations and terminations detailed within the scheme?
  • What ground and groundwater information does this design rely on?
  • What finish is planned over the coating, and has compatibility been confirmed?
  • If damp has been observed already, who has investigated the cause on site?
  • What is expected to happen if the structure cracks after the coating has been applied?

Blind spots

Commonly overlooked points

  • A rigid bonded coating and a structure that moves are an uneasy pairing, and the coating usually loses.
  • The material is part of a system, and using accessories from elsewhere changes what the manufacturer supports.
  • The substrate does more to determine the outcome than the choice of product does.
  • Below-ground work is a specialist discipline rather than a material choice made at a merchant's counter.
  • Applying a coating without addressing drainage tends to move a problem rather than resolve it.

What this page does not do

  • Below-ground waterproofing is a specialist design discipline and must be routed to a suitably qualified specialist; no coating is adequate on its own for any situation.
  • This reference contains no waterproofing specification, and nothing here should be read as a scheme, a method, or approval of any approach.
  • Damp observed in an existing building requires on-site investigation by a qualified professional before any material is chosen or any work is specified.
  • Where any layer of a scheme sits within the construction is design work for the specialist rather than something a general reference can state.

Related entries

Related materials

Materials from the same family, an adjacent role in the assembly, or a shared application.

Damp-proof membrane →A continuous sheet or liquid-applied moisture-control layer associated with floors and slabs, and a different product from the course built into walling.Damp-proof course →A moisture-resisting strip or course built into walling as it is constructed, distinct from the continuous area membrane associated with floors and slabs.Portland cement →The hydraulic binder that sets concrete, mortar, render and screed. It is one ingredient alongside aggregate and water, not the finished material itself.Cement render →A site-mixed or bagged sand-and-cement coating applied in successive coats onto masonry or lath, comparatively hard and dense, and normally finished with a paint or decorative topcoat.Masonry mortar →The bedding and jointing material that binds masonry units into a wall, and the component that usually decides how the finished wall moves, weathers and fails.Concrete block →Cast concrete masonry units, solid or hollow, used for inner leaves, partitions, substructure and retaining work where a dense and heavy unit is wanted.Reinforced concrete →Concrete with steel embedded in it, so the concrete resists compression while the reinforcement carries the tension that plain concrete cannot take.Tile backer board →A board fixed to walls and floors to give tiling a flat, stable and moisture-tolerant base; it is a substrate rather than a finish, and is not by itself a water-managing layer.Cement screed →A sand and cement layer laid to a thickness over a structural floor and worked level by hand, forming a true base for the floor finish above it.Engineering brick →Dense fired clay units turned to where low water absorption governs, such as below damp-proof course level, in retaining work and in the more exposed masonry details.

Inspiration

Related Ideas Library pages

Design directions where this material commonly appears.

Preparation

Related planning checklists

Owner-side preparation before the conversation where this material comes up.

Go deeper

Related Build Design Hub guides

Planning guidance and neutral comparisons behind the decisions on this page.

Sealants & Membranes

Reference entries for the thin control layers — joint sealants, damp-proof courses and membranes, vapour control layers, breather membranes, tanking systems, tapes and foams.

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