Silicone sealing

Silicone sealing is an elastic joint sealing that keeps moisture, air, dust, and pollutants away from structures while permanently accommodating movements. In practice, it appears across virtually all trades in structural and fit-out works-from fair-faced concrete to natural stone cladding. It also plays a role in the context of concrete demolition and special deconstruction, strip-out and cutting, as well as in rock demolition and tunnel construction: joints are protected prior to interventions, temporarily sealed, or re-established after mechanical separation methods. Wherever concrete demolition shear or rock and concrete splitters separate components in a controlled manner, a properly designed and executed silicone joint often determines whether adjacent components remain undamaged and whether a clean, restorable termination is achieved. As a cross-trade detail, it supports dust control, moisture management, and precise edge definition at interfaces and cut lines.

Definition: What is meant by silicone sealing?

Silicone sealing refers to sealing joints and connection areas with elastic silicone sealants. These sealants are permanently elastic, chemically resistant, aging-resistant, and able to accommodate movements in expansion and connection joints without tearing. Silicone joints are not load-bearing and do not replace structural waterproofing or drainage; they protect the joint and the adjacent building materials. Typical substrates include concrete, reinforced concrete, metal, ceramics, glass, and numerous natural stones-each with attention to adhesion and material compatibility. The elastomeric sealant ideally forms a two-flank bond over a correctly sized joint backing to minimize restraint and stress peaks.

Fields of application in concrete construction, deconstruction, and strip-out

In structural concrete construction, silicone joints seal movement and connection joints, for example between precast concrete elements, at window and door elements, or at building services penetrations. In gutting works and selective deconstruction, silicone sealings are often first released or removed to separate components in a controlled manner. This particularly concerns façade panels, glazing, and lightweight elements that should be relieved of stress before using concrete demolition shear or rock and concrete splitters. In wet cutting methods, temporary silicone beads can also limit the escape of slurry; after the intervention, the elastic sealing is re-established at the new cut edges. In tunnel and shaft areas, silicone-based connection sealings help minimize dust ingress, splash water, or drafts at temporary partition walls, cable penetrations, and bulkheads. In sensitive interior zones, perimeter seals around openings and temporary closures also contribute to noise reduction and cleaner workflows.

Material properties and silicone types

The selection of the sealant depends on substrate, movement, and exposure. Important types and properties:

• Curing systems: Acetoxy-curing silicones (smell of acetic acid) adhere well to glass and smooth surfaces; neutral-curing systems are more universal and usually more compatible with natural stone.
• Modulus and movement accommodation: Low-modulus silicones are particularly stretchable; high-modulus ones offer greater stability. The movement capability (e.g., ±20 to ±50%) must match the joint geometry.
• Application profiles: Sanitary silicones with fungicidal equipment for damp and wet rooms; façade silicones for exterior areas with UV and weather resistance; heat-resistant special formulations for elevated temperatures.
• Natural stone compatibility: Special, neutral-curing grades prevent edge discoloration (migration) on sensitive natural stones.
• Adhesion and primer: On dense, smooth, or critical substrates, suitable primers improve adhesion; for porous concrete, thorough pore cleaning is essential.
• Color and surface: Color-stable, low-chalking formulations with low dirt pickup enhance visual durability on exposed concrete and natural stone surfaces.
• Cure speed and climate: Skin formation and through-cure depend on joint size, humidity, and temperature-observe manufacturer specifications for staging follow-on work.

Planning and joint dimensioning

A functional silicone sealing begins with correct dimensioning and joint routing. The goal is a permanently elastic, two-sided adhesion without restraint.

Principles of dimensioning

• Width/depth: Often proven: joint depth ≈ 0.5 to 0.7 of the joint width (guideline), minimum width usually ≥ 6 mm. For large movements, dimension wider rather than deeper.
• Back-up material: Closed-cell backer rod (PE) prevents three-sided adhesion and defines the joint depth. Alternatively, bond breaker tape is used.
• Edge zones: Joint flanks must be sound, clean, and dry. Sanded or chalking zones must be removed.
• Movement classes: The expected component movements (temperature, shrinkage, loads) guide the choice of sealant and geometry.
• Adhesion width: Ensure sufficient bonding area on both flanks, typically ≥ 5 mm, with an hourglass profile for optimized stress distribution.

Execution: Work steps for a durable silicone joint

1. Assess and plan: Record joint type, movements, substrate, climate, and subsequent exposure. Define sequence with adjacent trades and temporary protections.
2. Prepare: Completely remove old sealants and residues; clean joint flanks free of dust and grease; ensure drying.
3. Backfilling: Insert appropriate backer rod, define joint depth, reliably avoid three-sided adhesion.
4. Masking: Create clean edges with suitable masking tape, especially on exposed surfaces.
5. Primer (if required): Apply thin and even per manufacturer’s instructions, observe flash-off time.
6. Application: Inject sealant free of bubbles, fill evenly; avoid voids. Work in a continuous pass to minimize cold joints.
7. Tooling: Shape the surface within skin formation time with an appropriate tooling agent, do not wet adhesion flanks. Prefer a slightly concave profile to accommodate movement.
8. Tape removal and curing: Remove tapes in time, observe curing time and climate, protect the joint from moisture exposure. Coordinate interim protection against dirt and impact.

Processing notes

• Temperature: Application typically at +5 to +40 °C; avoid direct sun and strong cooling.
• Moisture: Humidity promotes curing; standing water in the joint must be avoided.
• Substrate compatibility: Carry out preliminary adhesion and compatibility tests, especially on natural stone and coated metals.
• Adjacent materials: Check compatibility with paints, membranes, and tapes to prevent softening, staining, or loss of adhesion.

Interfaces with rock and concrete splitters and concrete demolition shear

In controlled separation work in concrete demolition and special demolition, silicone sealings influence the quality of the interfaces. In practice, recurring interfaces arise with rock and concrete splitters as well as with concrete demolition shear:

• Before cutting/separation: Elastic connection joints on adjacent components are cleanly cut open or removed to avoid cracks, spalling, and undesirable tensile stresses.
• Temporary sealings: Along saw cuts or core drilling, temporary silicone beads can limit the escape of water and slurry; this facilitates clean work in sensitive areas.
• After splitting or shear demolition: Newly created cut and butt joints are cleaned, reprofiled if necessary, and re-established with a suitable silicone joint-especially on exposed concrete surfaces, precast joints, or façade connections.
• Accompanying trades: When decoupling components connected to building services or façade elements, targeted release of silicone sealings prevents material damage and facilitates dismantling.
• Sequence and protection: Define execution sequence, splash protection, and dust barriers so that fresh silicone joints are not contaminated or mechanically damaged.

Quality assurance and typical failure patterns

A durable sealing results from suitable material selection, correct joint geometry, and clean execution. Typical errors can be avoided with clear inspection and work steps.

• Lack of adhesion at edge zones: Usually caused by dust, moisture, oil, or missing primer. Remedy: clean flanks, check adhesion promoters, create test areas.
• Three-sided adhesion: Leads to premature tearing. Remedy: install backer rod correctly or use bond breaker tape.
• Bubbles and voids: Caused by entrapped air or moisture. Remedy: inject without bubbles, keep climate stable.
• Discoloration on natural stone: Due to unsuitable sealants or plasticizer migration. Remedy: choose neutral-curing silicones compatible with natural stone.
• Cracks and tears: Result of incorrect dimensioning or a system that is too stiff. Remedy: size movement capability correctly, choose appropriate modulus.
• Mold growth: In permanently damp zones without fungicidal equipment or with maintenance issues. Remedy: choose suitable grade, observe surface care.

Acceptance criteria and documentation

• Geometry: Joint width and depth within tolerance; continuous backer rod support; uniform profile.
• Adhesion: Spot peel checks on sample sections; no edge detachment or cohesive failure.
• Surface: Clean edges without smearing; no pinholes, bubbles, or inclusions.
• Records: Document sealant type, batch, primers, climate, and test areas for traceability.

Occupational safety and environmental aspects

Silicone sealings are considered user-friendly; nevertheless, protective measures and careful handling are important.

• Emissions: Acetoxy-curing types can release acetic acid; ensure good ventilation.
• Personal protective equipment: Gloves, safety glasses, and suitable respiratory protection are advisable for intensive application.
• Cleaning and disposal: Remove fresh residues mechanically, collect cured silicones separately, and dispose of according to local regulations.
• Fire protection and temperature: Select sealant according to the intended use; consider elevated temperatures and open flames in the work environment.
• Handling: Observe safety data sheets; avoid incompatible solvents on sensitive substrates to prevent staining or loss of adhesion.

Special requirements in tunnel construction and with natural stone

In tunnel construction, silicone sealings are used primarily in fit-out trades and installations: cable penetrations, housing connections, temporary dust and splash-water barriers, and transitions at built-in components. The joints must be robust, aging-resistant, and maintainable. On natural stone surfaces-such as in façades or claddings after deconstruction works-material compatibility is paramount. Neutral-curing, natural-stone-compatible silicones and clean, dry flanks prevent edge discoloration and efflorescence. Where rock and concrete splitters or concrete demolition shear selectively release components, the visual quality of adjacent natural stones is preserved through controlled release and subsequent re-establishment of the silicone joints. In enclosed or low-ventilation areas, low-odor, non-corrosive systems and careful curing control support safe operation and consistent appearance.

Maintenance and renewal of silicone joints

Elastic joints are components requiring maintenance. Depending on exposure, they can age and should be visually inspected at regular intervals. For renewal, the sealant is completely removed, the joint is re-prepared, and closed with compatible material. For follow-up work on the structure, for example after using concrete demolition shear to adjust openings, it is advisable to immediately re-establish the silicone sealing at all affected connection joints to prevent moisture ingress and dirt edges. As a guideline, exterior joints in high UV and weather exposure warrant annual checks, while interior joints are often inspected in 2 to 3 year cycles or after significant component movements.

Legal and technical orientation

Planning and execution of silicone sealings are guided by recognized technical rules and the processing guidelines of the sealant manufacturers. Decisive are tested suitability for the respective substrate, the intended movement class, and the environmental conditions. Information on adhesion strength, temperature resistance, compatibility with natural stone, and the use of primers must be observed. Where applicable, ensure conformity with relevant classifications for modulus and movement capability, and maintain documentation for quality control. Binding assessments in individual cases cannot be derived from this; the project-specific requirements and on-site verification remain authoritative.