Repair Systems — 01
Backer Rod & Bond Breaker Tape
Technical product reference for closed-cell polyethylene foam backer rod and bond breaker tape used to control sealant depth, prevent three-sided adhesion and create correct sealant profile in movement joints on Australian balconies, podium decks and wet areas.
What are backer rod and bond breaker tape?
Backer rod is a closed-cell polyethylene foam cylinder installed in a movement joint before sealant application. Its two functions are: controlling the sealant depth (maintaining the correct depth-to-width ratio) and preventing three-sided adhesion. Three-sided adhesion occurs when sealant bonds to both joint faces and the joint base simultaneously — preventing the sealant from elongating freely under movement. When a joint with three-sided adhesion is subjected to cyclic building movement, the sealant tears at the weakest point (the joint base) rather than stretching at the joint faces.
Backer rod is specified as closed-cell foam only. Open-cell foam backer rod absorbs sealant chemistry and creates adhesion at the joint base — defeating its purpose. Backer rod diameter should be approximately 25% larger than the joint width to ensure a snug interference fit that maintains position during sealant application.
Bond breaker tape is a self-adhesive polyethylene film tape used as an alternative to backer rod in shallow joints, saw-cut expansion joints, and joints where round backer rod cannot be installed correctly due to joint geometry. The PE film does not bond to common sealant chemistries and provides the same bond-breaking function as backer rod in flat-bottomed joints.
Do not confuse backer rod with:
- Open-cell foam — open-cell foam absorbs sealant and causes three-sided adhesion — must not be used as backer rod
- Compressible filler board — expansion joint filler (foam or fibreboard) used to form the joint — installed before the structure is cast, not a sealant accessory
- Compression seals — pre-compressed cellular foam or EPDM profiles designed to be the sole joint seal — different product from backer rod which is used beneath a liquid sealant
Product Reference
3 products — 2 brands — backer rod and bond breaker tape — scroll to view all
System Description
Nomaflex is a closed-cell polyethylene foam backer rod widely used in Australian construction for sealant joint depth control and prevention of three-sided adhesion. Available in circular cross-section in a range of diameters to suit various joint widths. Installed by compressing slightly and pressing into the joint to the correct depth before sealant application. Closed-cell foam does not absorb sealant chemistry — maintains correct sealant profile and ensures two-sided adhesion only. Used in balcony and wet area movement joints, expansion joints in tiled decks, perimeter joints, and any joint requiring a flexible sealant with controlled sealant depth ratio. Select backer rod diameter slightly larger than the joint width (typically 25% oversize) to ensure a snug interference fit. Confirm diameter selection against the joint width and the required sealant depth ratio (typically 1:1 to 2:1 width to depth). // TODO: confirm current Nomaflex product range and diameter availability in Australia — Carpenter Co. products may be distributed under Nomaflex or related brand names in the Australian market.
Technical Properties
- Closed-cell polyethylene foam — does not absorb sealant — maintains correct sealant profile from application through cure
- Round cross-section — compresses to fit joint width — provides consistent sealant depth control
- Prevents three-sided adhesion — sealant bonds to two joint faces only — allows correct movement accommodation
Limitations
- Diameter must be correctly selected — undersized rod will not maintain sealant depth; oversized rod will be difficult to install and may distort the joint
- Not suitable for open-cell foam — open-cell backer rod absorbs sealant and compromises joint performance
- Do not use in joints that will be subject to continuous immersion without confirming PE compatibility with the sealant system
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Tremco CPG supplies closed-cell polyethylene foam backer rod as an accessory for use with Tremco sealant systems (Spectrem silicone, Vulkem polyurethane, and related products). Backer rod is specified as part of the Tremco sealant system specification to ensure correct joint geometry, sealant depth ratio, and prevention of three-sided adhesion. Available in a range of diameters. // TODO: Confirm current Tremco CPG Australia backer rod product designation and diameter range — consult Tremco CPG Australia for current accessory product list.
Technical Properties
- Closed-cell polyethylene foam — does not absorb sealant chemistry — maintains correct sealant profile
- Part of the Tremco sealant system specification — use with Tremco-specified sealants for warranted performance
- Prevents three-sided adhesion — ensures correct two-sided bond for movement accommodation
Limitations
- Confirm Tremco product designation and availability before specifying — may vary from European product range
- Correct diameter selection is critical — incorrect sizing compromises sealant depth control and joint performance
- Confirm current product specification and availability with Tremco CPG Australia before specifying
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Polyethylene bond breaker tape is a self-adhesive PE film tape applied to the base of a sealant joint as an alternative to round backer rod in situations where the joint is too shallow for backer rod or where the joint base is flat and backer rod cannot be installed correctly. The PE film does not bond to the sealant — it allows the sealant to cure with adhesion to only the two joint faces, preventing three-sided adhesion. Typically used in very shallow rebated joints, saw-cut expansion joints in concrete, and surface-applied joints where depth control with backer rod is not practical. Not suitable as a substitute for backer rod in all situations — confirm the joint geometry and expected movement before selecting tape over rod. // TODO: Confirm current product availability — PE bond breaker tape is supplied by various sealant system manufacturers and general trade suppliers; no single dominant brand in the Australian market. Confirm with Sika, Tremco, or ARDEX technical for system-specific recommendation.
Technical Properties
- Polyethylene film — does not bond to common sealant chemistries (silicone, PU, polysulfide) — provides reliable bond-breaking at joint base
- Self-adhesive backing — applied to the joint base before sealant application
- Flat profile — suitable for saw-cut and rebated joints where round backer rod cannot be installed
Limitations
- Not a substitute for backer rod in deep joints — backer rod provides better sealant depth control in joints wider than approximately 15 mm
- Tape must be fully adhered to the joint base without voids or lifted edges — incomplete adhesion allows sealant to bond to the joint base
- Do not use in joints subject to significant hydrostatic pressure or continuous immersion without confirming suitability
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Comparison
Side-by-side comparison of backer rod and bond breaker tape products. Select closed-cell foam only — confirm diameter with sealant manufacturer.
| Product | Supplier | Type | Profile | Foam type | Diameter / size range | Primary use |
|---|---|---|---|---|---|---|
| Nomaflex Closed-Cell Backer Rod | Nomaflex / Carpenter Co. | Backer rod | Round | Closed-cell PE | Various — 10 mm to 50 mm+ (confirm with supplier) | Movement joints — internal angle, perimeter, expansion joints |
| Tremco Closed Cell Backer Rod | Tremco CPG | Backer rod | Round | Closed-cell PE | Various — confirm with Tremco CPG AU | Tremco sealant system specified joints |
| Polyethylene Bond Breaker Tape | Various | Bond breaker tape | Flat / self-adhesive | N/A — PE film | N/A — various tape widths | Shallow / saw-cut / rebated joints where round backer rod cannot seat correctly |
Brand Equivalents
Backer rod and bond breaker tape equivalents. Closed-cell PE backer rod is a commodity product — confirm brand and diameter availability through the sealant system manufacturer or local trade supplier.
| Product type | Nomaflex | Tremco | Various |
|---|---|---|---|
| Closed-cell PE backer rod — round | Nomaflex Backer Rod | Closed Cell Backer Rod | Various — confirm with sealant mfr |
| Bond breaker tape — flat | — | — | PE tape — confirm with sealant mfr |
Critical installation requirements — backer rod and bond breaker tape
- Use closed-cell polyethylene foam only — open-cell foam backer rod absorbs sealant chemistry and creates three-sided adhesion, defeating the purpose of the backer rod
- Three-sided adhesion failure is the most common sealant joint failure mode — backer rod or bond breaker tape is not optional in any movement joint
- Backer rod diameter must be selected to be approximately 25% larger than the joint width — it is installed by compression to ensure a snug fit and correct depth control
- Bond breaker tape must be fully adhered to the joint base with no voids — any unbonded section will allow sealant adhesion at that point
Disclaimer
Information is general only. Backer rod and bond breaker tape selection must be confirmed against the sealant product specification, joint geometry, substrate conditions, and the current manufacturer technical data sheet. AS 3740 requires flexible sealant at all internal angles — correct joint preparation including backer rod is mandatory. Do not rely on this reference as a substitute for professional waterproofing consultant advice.