Repair Systems — 03 — Facade & External Envelope
Flexible crack filler systems
Technical product reference for flexible crack filler systems used in non-structural facade cracking remediation on Australian Class 2 strata buildings. Covers paintable elastomeric fillers, polymer-modified crack fillers and flexible acrylic sealants for hairline-to-moderate width cracks in rendered and masonry facade surfaces — where some accommodation of ongoing minor movement is required.
What are flexible crack filler systems?
Flexible crack filler systems are elastomeric or flexible polymer-based materials applied to fill and bridge non-structural cracks in facade surfaces — rendered, masonry and concrete — where the filled crack must accommodate some ongoing minor movement without re-cracking. Unlike rigid fillers (cementitious patching, epoxy fillers), flexible crack fillers remain pliable after cure, allowing the filled crack to open and close slightly with thermal movement without breaking down the repair.
Product Reference
3 products — 3 brands — flexible crack filler systems — scroll to view all
Sika SikaFill-300
Elastomeric crack bridging coating — non-structural facade cracks
System Description
Sika SikaFill-300 is an elastomeric crack bridging coating and filler suitable for sealing and bridging fine to moderate width non-structural facade cracks in rendered and masonry surfaces. It is applied by brush or roller as a flexible coating that bridges hairline to moderate cracks and accommodates minor ongoing movement. SikaFill-300 is used in Australian strata facade remediation as a crack repair layer applied under a facade coating system, providing flexibility that rigid fillers cannot offer. It is paintable once cured. Do not use for structurally active cracks, wide cracks or cracks with significant ongoing movement — these require a movement joint sealant system with backer rod. Confirm suitability, application method and crack width limits from the current Sika TDS. TODO: owner confirm — confirm current product designation, crack width capacity and compatibility with final coating with Sika Australia technical.
Technical Properties
- Elastomeric — flexible after cure — bridges fine to moderate non-structural cracks
- Paintable — can be coated over with facade paint systems
- Suitable for rendered and masonry facade surfaces
Limitations
- Not suitable for structurally active cracks — engineering assessment required before application
- Not suitable for wide movement joints — use sealant-backed movement joint system for wide or active joints
- Not suitable as a waterproofing membrane — a dedicated membrane system is required for waterproofing over cracked substrates
PROCUREMENT SOURCES
Confirm suitability with current manufacturer TDS. Always assess crack type before specifying repair.
Bostik Seal N Flex Facade
One-part PU flexible crack sealant — facade cracks — paintable
System Description
Bostik Seal N Flex Facade is a one-part polyurethane sealant suitable for use as a flexible crack filler in facade crack remediation on rendered and masonry surfaces. It is paintable once cured — an important advantage for facade work where the repair must be overcoated with facade paint or coating. One-part PU crack fillers are applied by cartridge gun into the cleaned crack, then struck off flush with the surface once cured, and overcoated. For cracks wider than hairline, the crack should be chased (widened) to form a proper sealant joint with parallel faces and correct width-to-depth ratio before applying the sealant. Do not apply into V-shaped cracks without first forming a parallel-sided joint. Confirm current product designation, crack width capacity and paintability from the current Bostik TDS. TODO: owner confirm — confirm current product designation, application method and crack width capacity with Bostik Australia.
Technical Properties
- One-part — no mixing — ready to apply from cartridge
- Paintable after cure — suitable for overcoating with facade paint
- Flexible — accommodates minor ongoing movement in non-structural cracks
Limitations
- Not suitable for structurally active or wide movement cracks
- Not suitable for waterproofing without a dedicated membrane over
- Crack must be clean and dry before application
PROCUREMENT SOURCES
Confirm suitability with current manufacturer TDS. Always assess crack type before specifying repair.
Selleys No More Gaps Exterior
Flexible acrylic filler — exterior facade — hairline cracks — paintable
System Description
Selleys No More Gaps Exterior is a flexible acrylic exterior filler suitable for filling hairline to fine cracks in render, masonry and concrete facade surfaces prior to repainting. It is widely available through Australian hardware and trade channels and is the most commonly used product for minor facade crack touch-up and pre-paint preparation in strata remediation. Acrylic fillers have lower movement accommodation than polyurethane or elastomeric crack fillers — they are suitable for hairline cracks that are stable or have minimal ongoing movement, but not for cracks with significant width or active thermal or structural movement. Selleys No More Gaps Exterior is water-based, easy to apply, cleans up with water and is paintable once cured. For cracks wider than approximately 2mm, a PU or elastomeric sealant filler is more appropriate. Confirm suitability for the specific crack type and width from the current Selleys TDS.
Technical Properties
- Water-based acrylic — easy application, water cleanup
- Paintable after cure — compatible with most exterior architectural paints
- Exterior rated — suitable for Australian outdoor conditions for hairline cracks
Limitations
- Lower movement accommodation than PU or elastomeric fillers — not suitable for active or thermally wide cracks
- Not suitable for cracks wider than approximately 2mm without specialist assessment
- Not suitable for structurally active cracks
PROCUREMENT SOURCES
Confirm suitability with current manufacturer TDS. Always assess crack type before specifying repair.
System Comparison
Flexible crack filler comparison. Confirm suitability for crack type and width. Engineering assessment required before repair.
| Product | Brand | Type | Movement | Paintable | Crack suitability | Primary use |
|---|---|---|---|---|---|---|
| SikaFill-300 | Sika | Elastomeric | Moderate — crack bridging | Yes | Hairline to moderate width | Crack bridging coating under facade paint on rendered and masonry facades |
| Seal N Flex Facade | Bostik | One-part PU | Moderate — flexible sealant | Yes | Hairline to moderate width | Non-structural facade crack filling before overcoating in strata remediation |
| No More Gaps Exterior | Selleys | Acrylic | Low — hairline cracks only | Yes | Hairline to 2mm | Hairline crack touch-up before repainting — minor defects only |
Do not use flexible crack filler for:
- Structural cracks (cracks from structural movement, settlement or active cracking require engineering assessment — a facade consultant or structural engineer must assess the crack cause before any repair is attempted)
- Active wide movement joints (where crack widths are significant or ongoing — a sealant-backed movement joint system is required, not a crack filler — listed on the movement joint sealant systems page)
- Cracks requiring epoxy crack injection (live structural cracks or cracks in structural elements — epoxy injection is used for structural repair — different product category)
- Waterproofing over wide cracks (a flexible membrane system is required for waterproofing over cracked substrates — not a crack filler alone)
- Cracks indicating underlying active defects (spalling, corrosion, delamination — crack filler applied over these defects will fail — remediate the underlying cause first)
Disclaimer
This page provides general technical information only. Facade cracks must be assessed by a qualified building consultant, facade engineer or remedial building practitioner before specifying any repair system. Do not apply crack fillers over structurally active cracks without engineering assessment.