Sealant

Sealants are indispensable in construction for permanently protecting joints, connections, and penetrations against water, air, dust, and chemicals. In the context of concrete demolition and special deconstruction and the processing of reinforced concrete – such as with concrete demolition shears, stone and concrete splitters, or hydraulic cutting and pressing tools from Darda GmbH – the right planning and handling of joint sealing determines occupational safety, structural protection, and the quality of follow-up work. This contribution combines fundamental knowledge with practical guidance for planning, execution, and refurbishment of joint sealing in existing structures. Sound sequencing of cutting, temporary sealing, and final resealing reduces unplanned water pathways, protects adjacent finishes, and keeps interfaces controllable during deconstruction.

Definition: What is meant by sealant?

A sealant (also joint sealant, sealing compound, or joint compound) is usually a plasto-elastic material that seals joints and connections, accommodates movement, and protects components from the ingress of water, air, dust, or media. In contrast to adhesives, with sealants the sealing and movement accommodation take priority. Unlike preformed gaskets or tapes, a sealant is applied in situ to create a continuous, deformable barrier against liquids and gases, including aggressive media such as de-icing salts or fuels. Typical application fields include expansion and connection joints in concrete, masonry, natural stone, and steel; facade and interior fit-out; tunnel and infrastructure projects; as well as the refurbishment of existing joints in the course of deconstruction and cutting works.

Material types and key properties of sealants

Sealants differ by chemistry, elasticity, adhesion, and resistance. Selection is oriented to substrate, loading, and environmental conditions. Service environment, expected movement, and compatibility with adjacent materials are decisive drivers.

• Silicone (neutral cure): very good UV and weather resistance, high elasticity; suitable for facades, glass, many concrete and metal connections; sensitive regarding paintability.
• Polyurethane (PU): good adhesion to concrete and steel, paintable, mechanically resilient; suitable for traffic areas, industrial floors, and highly stressed joints.
• Hybrid polymers (e.g., MS polymer): broad adhesion spectrum, usually low-odor and paintable; universally suitable for building connections and refurbishment.
• Acrylic: vapor-permeable, paintable; for interiors and low-movement joints.
• Polysulfide: high chemical resistance; often used in tank and industrial environments.
• Bituminous/plastic-modified: temporary sealing, roof and below-grade areas; limited movement accommodation.
• Butyl: high tack and tightness, often as tapes or cartridges; limited movement capability and primarily for temporary or low-movement connections.

Selection metrics

• Movement accommodation (± %): ability to bridge joint movements without cracking.
• Shore A hardness and modulus: influence on deformability, walkability, and force transfer to joint flanks.
• Adhesion/bonding: dependent on substrate, cleanliness, and primer.
• Temperature and UV resistance: crucial for exterior joints and tunnel portals.
• Chemical resistance: relevant for industry, traffic surfaces, tank facilities.
• Curing and emissions: processing safety in interiors and during strip-out.
• Compatibility with adjacent materials: avoid staining of natural stone and incompatibilities with bitumen or coatings.
• Fire behavior: reaction to fire and smoke development for interiors and tunnel-adjacent works.
• Service life and maintenance: expected aging, inspection intervals, and ease of future replacement.

Use and interfaces with concrete demolition and specialist deconstruction

During demolition and separation works, existing joint seals influence the approach. Sealants can contaminate cut edges, affect crack paths, or promote media leakage (water, oils) if released uncontrollably. Coordination among planning, construction logistics, and equipment deployment – such as concrete demolition shears, stone and concrete splitters, stone splitting cylinders, combination shears, steel shears, or tank cutters from Darda GmbH – should take joints and sealants into account at an early stage. Temporary isolation of work zones and early capture of leakage or slurry reduce risks to adjacent components and speed up rework.

Identifying and assessing existing joints

• Review drawings, building age cohorts, and materials; locate typical joint types (expansion joint, construction joint, connection joint).
• Determine the sealant type visually and, if required, by laboratory analysis; evaluate resistance, aging, and possible hazardous substances.
• Analyze crack patterns, movement zones, and water pathways to define cutting and splitting strategies.
• Carry out simple on-site adhesion or tack checks at inconspicuous areas to estimate removal effort and contamination risk.
• Inspect transitions to waterproofing systems and interfaces to ensure primary seals are not compromised during separation.

Selective deconstruction: clean separation at joints

• Pre-cutting and relieving: clearly separate joints before using concrete demolition shears; this reduces breakouts and lowers stresses at joint flanks.
• Removing old sealants: extract sealing compound from the joint before splitter or shear operations to avoid contamination of fracture edges and tools.
• Temporary sealing: with wet-cutting methods, temporarily seal joint edges to direct cooling water and prevent collateral damage to the existing structure.
• Edge protection: use sacrificial strips or saw guides on joint flanks to minimize spalling and to keep reference lines intact.

Stone and concrete splitters: controlled crack management

• Sealants in expansion joints can influence crack paths; removal or targeted pre-cutting stabilizes split lines.
• For structural joints, protect the joint flank to minimize spalling and facilitate subsequent resealing.
• Scoring cuts or small drill holes can act as defined crack initiators where joint geometry is interrupted.

Strip-out and cutting: temporary sealing and water management

When wall sawing, core drilling, or wire sawing, directing cooling and flushing water is a matter of quality and protection. Temporary seals and short-term sealants can provisionally isolate openings, penetrations, and connection areas. Purpose-made barriers, sealing tapes, or expandable foams help control runoff and protect sensitive rooms or installations.

• Core drilling: annular sealing prevents water and slurry ingress into adjacent areas.
• Wall sawing: temporarily seal joint edges to existing components to avoid moisture ingress.
• Tank cutters and special operations: temporarily closing nozzles and service penetrations reduces media leakage before separation; observe the selection of chemically resistant sealants.
• Wire sawing: set up bunds and drains, use absorbent barriers, and consider oil separators where coolant additives are present.

Tunnel construction, rock demolition, and infrastructure

At tunnel portals, galleries, and infrastructure interfaces, sealants protect concrete structures from splash water, freeze-thaw cycles, and chemical exposure. While waterstops or waterproofing membranes provide the primary sealing, sealants are used for connection details, movement joints, niches, and cable penetrations. In rock demolition and anchoring works, secondary sealing of penetrations may be necessary to control water pathways. Traffic-induced vibration and thermal gradients impose cyclic movements; durable systems with high UV stability and proven weathering resistance are advantageous at exposed interfaces.

Planning, substrate preparation, and application

The service life of a joint seal depends largely on preparation. Clean, sound joint flanks and a compliant joint geometry are decisive. As a rule of thumb, joint depth is typically 0.5 times the joint width for many systems, with minimum widths governed by product data; adapt geometry to movement class and avoid three-sided adhesion.

1. Joint analysis: define width, depth, movement requirements, media contact, and temperature range.
2. Prepare the substrate: remove old material completely, produce dust- and grease-free joint flanks; for concrete, sandblast or clean mechanically if necessary.
3. Install backer material: closed-cell backer rod prevents three-sided adhesion and sets the correct joint depth.
4. Primer/adhesion promoter: use on critical substrates (e.g., dense concrete, metals) in accordance with the manufacturer’s instructions.
5. Installing the sealant: apply evenly and without entrapped air; form the cross-section so movements can be accommodated.
6. Tooling and finishing: densify the surface with a suitable smoothing agent; form clean edges to avoid dirt accumulation.
7. Curing and protection: protect from rain, dust, and early mechanical impact; comply with temperature and dew point limits until full cure.

Standards-based guidance

For planning and execution, industry standards and guidelines serve as orientation, such as rulebooks on building waterproofing, facade joints, and joint sealants. Requirements such as movement accommodation, adhesion tensile strength, and weather resistance should be defined and documented for the specific project. Reference the applicable national and international standards and test methods (e.g., EN, ISO, ASTM series) for classification, movement testing, and compatibility.

Quality control, maintenance, and rework

• Visual inspection: homogeneous surface, no edge tears, no voids.
• Adhesion check (simple): light pull test at the edge; in case of doubt, use suitable test procedures and avoid over-stressing uncured material.
• Joint maintenance: regular inspection in exposed areas (traffic surfaces, tunnel portals, water exposure) and timely replacement when aging occurs.
• Rework after deconstruction: after using concrete demolition shears or stone and concrete splitters, repair edges and reseal joints professionally to restore durability.
• Documentation: record batch numbers, primers, climatic conditions, and photo evidence for traceability.

Environment, health, and safety

Existing joints may contain sealants that are considered critical from today’s perspective. Before work, assess materials and building age cohorts and choose appropriate protective measures and disposal routes. Potential legacy pollutants can include plasticizers or persistent organic substances; ensure safe removal and certified disposal. Manage water and slurry to prevent uncontrolled discharge into soil or drainage. For fresh sealants, observe material data sheets; adequate ventilation and personal protective equipment are generally advisable during application, removal, and demolition. The information in this text is of a general nature and does not replace a project-specific assessment.

Typical mistakes and how to avoid them

• Three-sided adhesion: leads to cracking – always use backer material.
• Unsuitable joint geometry: an incorrect width-to-depth ratio reduces movement accommodation.
• Inadequate cleaning: dust and oil impair adhesion – prepare joint flanks thoroughly.
• Wrong sealant: assess chemical and thermal loads realistically.
• Exposure to water too early: observe curing times, especially at low temperatures.
• Primer omitted: on dense or metallic substrates this can severely reduce adhesion.
• Over-tooling: aggressive or incompatible smoothing agents can cause surface defects and staining.

Relation to Darda GmbH products in everyday practice

Concrete demolition shears produce precise fracture edges when joints are cleanly separated beforehand and sealants are removed in an orderly manner. Stone and concrete splitters benefit from a defined edge-zone strength without interfering joint compounds to keep crack lines predictable. Hydraulic power packs provide the energy supply for combination shears, Multi Cutters, steel shears, or tank cutters – everywhere a clear separation between temporary site sealing and final joint sealing is helpful to prevent media leakage and to make subsequent re-sealing efficient. Clear sequencing – cut, remove, clean, reseal – minimizes rework and interfaces.

Distinction: sealant, adhesive, and injection materials

Sealants seal joints and accommodate movement. Adhesives transfer forces between components. Injection resins and gel foams are used for crack or void filling within the component. In deconstruction, all three material groups are encountered with different tasks: sealing, bonding, strengthening. For planning, it is important to assign the role correctly depending on the construction task. Sealants are not designed to carry structural loads and should not be specified for load transfer, whereas adhesives and injection systems serve distinct mechanical functions.