Repair Systems — 03
Failed Sealants & Joints — Facade
Technical product reference for one-part and two-part PU sealants, neutral-cure silicone, polysulfide sealants, backer rod and primer systems for failed facade sealant joints in Class 2 strata buildings in Australia.
What are facade joint sealant systems?
Facade joint sealant systems seal the movement joints, control joints, expansion joints and perimeter gaps in the external envelope of multi-storey buildings. These joints are essential to the weatherproofing performance of the facade — they accommodate thermal expansion, structural movement and differential settlement between facade elements while maintaining a continuous weather barrier. On Class 2 strata buildings, failed facade sealant joints are one of the most common sources of water ingress into common property and private lots.
The three primary sealant chemistries used in Australian facade joint remediation are one-part polyurethane, neutral-cure silicone, and two-part polysulfide. One-part PU sealants are moisture-curing, paintable and suitable for concrete, masonry and render facades. Neutral-cure silicone is the correct choice for joints against anodised aluminium, glass, coated metals and curtain wall framing — it is non-corrosive and UV stable. Two-part polysulfide sealants provide excellent adhesion and chemical resistance on precast concrete panel perimeter joints and masonry expansion joints, with a long track record in Australian facade construction.
All facade sealant joints must be formed over closed-cell backer rod to prevent three-sided adhesion, maintain the correct joint width-to-depth ratio (2:1), and allow the sealant to flex freely with facade movement. Primer is mandatory on concrete, masonry and metal substrates for reliable long-term adhesion — omission of primer is a leading cause of adhesive failure in remediated facade joints. AS 4386 provides the classification framework for facade joint sealants in Australia.
Do not confuse with:
- Acetoxy-cure (acid-cure) silicone — corrosive to metals and anodised aluminium — never use on metal facade substrates or curtain wall framing
- Tile wet area sealants — rated for interior wet area use only — not formulated for facade UV and weathering exposure
- Structural adhesives — bond components together and do not accommodate joint movement — not a sealant substitute
Product Reference
5 products — 4 brands — facade joint sealant systems — scroll to view all
System Description
Sikaflex Pro-3 is a premium one-part moisture-curing polyurethane sealant formulated for facade movement joints, expansion joints and curtain wall perimeter sealing on Class 2 strata buildings. It is applied by cartridge gun into prepared joints over closed-cell backer rod and is suitable for horizontal, vertical and overhead joints on concrete, masonry, render and metal facades. The product accommodates the thermal and structural movement demands typical of multi-storey facades and is paintable after full cure, making it appropriate where facade coatings are applied over sealed joints. Sikaflex Pro-3 is specified by facade consultants and remedial contractors for re-sealing failed control joints, expansion joints between precast panels, and perimeter joints at aluminium curtain wall frames and window/door surrounds. Confirm current product designation, movement accommodation class and compliance with AS 4386 requirements with Sika Australia before specifying. Backer rod and Sika Primer-215 are typically required as part of the complete joint system. Do not apply to contaminated, damp or inadequately primed joint faces. Clean, dry substrate with appropriate primer is mandatory for reliable adhesion on concrete and masonry facades.
Technical Properties
- One-part polyurethane — moisture-curing — no on-site mixing required — reduces application error on multi-storey facade access
- Paintable after full cure with compatible exterior paint systems — confirm paint compatibility with Sika technical before specifying
- Good movement accommodation — suitable for facade control and expansion joints subject to thermal and structural movement
Limitations
- Backer rod mandatory in all facade joints — three-sided adhesion causes premature cohesive failure — joint width/depth ratio must be maintained
- Primer required on most facade substrates including concrete, masonry and metal — confirm primer selection with Sika technical and current TDS
- Not for use in structural glazing applications without specific Sika approval — confirm load-bearing joint suitability with Sika technical
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Tremco Spectrem 2 is a high-modulus one-part neutral-cure silicone sealant formulated for structural glazing, facade curtain wall expansion joints and weather sealing of metal framing systems. Neutral-cure chemistry is non-corrosive to anodised aluminium, metal framing, coated metals and glazing — making it the appropriate choice for joints between glass, aluminium framing members, and facade panels on multi-storey Class 2 strata buildings. It is used in both new facade construction and remediation of failed structural silicone joints. Spectrem 2 provides high structural performance and UV resistance appropriate for exposed facade joints subject to weathering, UV and wind loading. It should be applied to clean, dry and correctly primed substrates following the Tremco substrate primer schedule. Confirm structural glazing suitability and compliance with glazing engineer and Tremco CPG technical before specifying in structural applications. Confirm whether Spectrem 2 remains the current active product designation in the Tremco CPG Australia range before specifying — product names are subject to periodic revision.
Technical Properties
- High-modulus neutral-cure silicone — non-corrosive — suitable for anodised aluminium, coated metals, glass and most facade substrates
- One-component — no mixing required — suitable for facade remediation in restricted or elevated access conditions
- UV stable after cure — appropriate for exposed facade joints subject to direct solar radiation on north-facing facades
Limitations
- Not paintable after cure — silicone joints cannot be overpainted — colour selection must be confirmed against facade finish before application
- Silicone-to-silicone re-sealing requires full mechanical removal of all existing cured silicone — new silicone will not bond to cured silicone
- Primer required on most non-glass substrates — confirm Tremco primer schedule for concrete, masonry and coated metal substrates
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Bostik Seal-N-Flex Pro is a one-part moisture-curing polyurethane sealant for facade movement joints, expansion joints and precast concrete panel perimeter sealing on multi-storey Class 2 strata buildings. Applied by cartridge gun over closed-cell backer rod to prepared, primed joint faces, it accommodates the thermal and structural movement demands of external facade joints. The product is paintable after full cure, enabling re-coating of the sealed facade surface as part of a complete facade remediation program. Seal-N-Flex Pro is suitable for vertical and horizontal joints on concrete, render and masonry facades, around precast panel perimeters, and at expansion joint interfaces between facade zones. It is part of the Bostik facade sealing system — confirm compatible primer selection and preparation requirements with the current Bostik technical data sheet. Confirm that Seal-N-Flex Pro is the current correct Bostik product designation for facade PU movement joint sealant in the Australian market before specifying.
Technical Properties
- One-part polyurethane — moisture-curing — no on-site mixing required — suitable for facade remediation under working access conditions
- Paintable after full cure with compatible exterior paint systems — confirm paint compatibility with Bostik technical before specifying
- Suitable for concrete, render and masonry facade substrates — confirm primer requirements with Bostik TDS
Limitations
- Backer rod mandatory in all facade joints — three-sided adhesion will cause premature joint failure — do not omit backer rod
- Primer required on porous and contaminated substrates — confirm primer selection with Bostik technical and current TDS
- Do not apply to damp, frozen or excessively hot joint faces — substrate temperature must be within product application range per TDS
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Illbruck ME300 Polysulfide
Two-part polysulfide sealant for precast and masonry joints
System Description
Illbruck ME300 Polysulfide is a two-part polysulfide sealant designed for precast concrete panel joints and masonry expansion joints on facades of multi-storey buildings. Two-part polysulfide chemistry provides excellent chemical resistance and adhesion to concrete and masonry substrates and has a long track record in Australian facade sealing. The product is mixed on site from base and activator components and applied by gun or spatula into prepared joints over closed-cell backer rod. Polysulfide sealants are particularly suited to precast concrete panel perimeter joints, expansion joints in masonry facades, and joints subject to exposure to fuel, oil or chemical contaminants. They exhibit lower movement accommodation than polyurethane sealants in some formulations — confirm movement accommodation class against joint design requirements with the current Tremco CPG technical data sheet before specifying. Confirm whether Illbruck ME300 Polysulfide is the current active product designation in the Tremco CPG Australia Illbruck range before specifying — product names are subject to periodic revision.
Technical Properties
- Two-part polysulfide chemistry — excellent adhesion to concrete and masonry — well-proven track record in Australian facade panel joint sealing
- Chemical resistance — suitable for joints exposed to mild chemical contamination, fuel and oils where PU sealants may not be appropriate
- Mixed on site from two-component system — pot life management required on site — follow Tremco CPG mixing and pot life guidance
Limitations
- Two-component mixing required on site — mixing error can compromise cure and joint performance — trained applicator mandatory
- Pot life limited after mixing — do not mix more material than can be applied within the stated pot life from the TDS
- Backer rod mandatory in all precast and masonry joints — three-sided adhesion compromises movement accommodation and causes premature failure
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Sika Primer-215 is a solvent-based primer formulated to improve the adhesion of Sikaflex polyurethane sealants to concrete, masonry and metal substrates on facade joint remediation projects. Applied by brush or swab to clean, dry joint faces immediately prior to sealant application, Primer-215 penetrates porous substrates and activates the joint face to improve sealant-to-substrate adhesion and reduce the risk of adhesive failure at the interface. Primer is not optional on facade joint remediation — many adhesive sealant failures on concrete and masonry facades are caused by inadequate surface preparation and omission of primer. Primer-215 is specified as part of the Sikaflex Pro-3 joint system for facade applications and must be applied and allowed to flash off per the current Sika TDS before sealant application commences. Confirm the current primer specification for each substrate type with the Sika Primer-215 technical data sheet and Sika Australia technical support. Primer selection must be matched to the specific sealant product and substrate combination.
Technical Properties
- Solvent-based primer — penetrates porous concrete and masonry substrates to activate joint face for improved PU sealant adhesion
- Suitable for concrete, masonry, render and metal substrates — confirm suitability for coated or treated metal facades with Sika technical
- Applied by brush or lint-free swab to clean, dry joint faces — thin even coat — allow to flash off before sealant application per TDS
Limitations
- Solvent-based — adequate ventilation required — do not use in confined spaces without forced ventilation and appropriate PPE
- Not a standalone sealant or waterproofing product — must be used as part of a complete Sika PU sealant joint system
- Do not apply to damp, dusty or contaminated joint faces — substrate preparation is the foundation of primer effectiveness
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Comparison
Side-by-side technical comparison of facade joint sealant products. Confirm current product specifications with manufacturer TDS.
| Product | Brand | Chemistry | Cure type | Paintable | Primer required | Movement accomm. | Primary use |
|---|---|---|---|---|---|---|---|
| Sikaflex Pro-3 | Sika | Polyurethane | Moisture-cure (1C) | Yes (confirm with Sika) | Yes — Primer-215 | High — confirm TDS | Facade movement & expansion joints — curtain wall perimeter |
| Tremco Spectrem 2 | Tremco | Neutral-cure silicone | Condensation-cure (1C) | No | Yes on non-glass (confirm TDS) | High — confirm TDS | Structural glazing — curtain wall expansion joints |
| Bostik Seal-N-Flex Pro | Bostik | Polyurethane | Moisture-cure (1C) | Yes (confirm with Bostik) | Yes on porous substrates | High — confirm TDS | Facade movement joints — precast panel perimeters |
| Illbruck ME300 Polysulfide | Tremco | Polysulfide | Two-component chemical cure | Confirm TDS | Yes — confirm TDS | Moderate — confirm TDS | Precast panel joints — masonry expansion joints |
| Sika Primer-215 | Sika | Solvent-based primer | N/A (primer only) | N/A | N/A | N/A | PU sealant adhesion primer — concrete, masonry, metal |
Brand Equivalents
Facade sealant equivalents across brands active in Australian Class 2 strata remediation.
| System type | Sika | Tremco | Bostik |
|---|---|---|---|
| PU facade sealant (1C, paintable) | Sikaflex Pro-3 | — | Seal-N-Flex Pro |
| Neutral-cure silicone (structural glazing) | — | Spectrem 2 | — |
| Polysulfide sealant (2C, precast) | — | Illbruck ME300 | — |
| PU sealant primer | Primer-215 | — | — |
Backer rod mandatory in facade joints
- Three-sided adhesion in facade sealant joints causes premature cohesive failure — closed-cell backer rod must be installed in all joints wider than 5mm before sealant application. Without backer rod, the sealant bonds to the bottom of the joint as well as the two sides, preventing the hourglass deformation required for movement accommodation and causing the sealant to split under thermal cycling.
- Joint width-to-depth ratio must be maintained at approximately 2:1 — for example, a 20mm wide joint should have a sealant depth of approximately 10mm. Backer rod controls this ratio by setting the joint depth. Over-deep sealant joints are stiffer and accommodate less movement; over-shallow joints have insufficient bond area and are prone to adhesive failure.
- Closed-cell polyethylene backer rod is the standard specification for facade joints — it is non-absorbent, compressible, and does not bond to the sealant (providing the bond break on the third face). Open-cell backer rod absorbs moisture and is not suitable for facade weatherproofing joints.
- Confirm backer rod diameter against joint width — backer rod should be 25% larger than the joint width so it compresses into the joint and seats correctly without movement. Undersized backer rod will not seat correctly and will allow sealant to wrap around and bond to the third face.
Disclaimer
Information is general only. Sealant selection must be confirmed against joint width, substrate, expected movement, chemical exposure, and the current manufacturer technical data sheet. Do not rely on this reference as a substitute for professional facade consultant advice.