Repair Systems
Backer rods
Closed-cell polyethylene foam backer rod — technical reference for concrete cracking in Australian remedial building practice. Covers system selection, product comparisons, and brand equivalents.
What is backer rods?
Backer rods are closed-cell or open-cell foam cylinders inserted into a joint recess before sealant application, providing a backing that controls sealant depth and prevents three-sided adhesion. Correct sealant geometry — approximately 2:1 width-to-depth ratio — is critical for sealant performance: too deep a bead cannot stretch freely and will tear at the bond line under joint movement; three-sided adhesion prevents the sealant from functioning as intended. Backer rods are installed in all sealant joint reinstatements in concrete and masonry, whether the joint is an original construction joint or a chased slot cut specifically for new sealant. Diameter selection is based on joint width — the backer rod should compress approximately 25% when pushed into the joint to create a firm, consistent backing. Closed-cell polyethylene types are required with silicone sealants to prevent off-gassing and surface bubbling.
Product Reference
Scroll right to see all brands. Use each card's TDS link for verified specifications before specifying on any project.
System Description
Insert to control sealant depth at 1:1 width to depth. Prevents 3-point adhesion. Slightly oversized for compression.
Technical Properties
- Maintains correct 2:1 width-to-depth sealant aspect ratio, preventing three-sided adhesion
- Reduces sealant volume required — improves economy on long joint runs
Limitations
- Over-sized backer rod stretches and may crack the sealant — diameter selection is critical
- Closed-cell type only with silicone sealants — open-cell causes off-gassing and bubbling
PROCUREMENT SOURCES
System Description
Insert to control sealant depth at 1:1 width to depth. Prevents 3-point adhesion. Slightly oversized for compression.
Technical Properties
- Maintains correct 2:1 width-to-depth sealant aspect ratio, preventing three-sided adhesion
- Reduces sealant volume required — improves economy on long joint runs
Limitations
- Over-sized backer rod stretches and may crack the sealant — diameter selection is critical
- Closed-cell type only with silicone sealants — open-cell causes off-gassing and bubbling
PROCUREMENT SOURCES
System Description
Insert to control sealant depth at 1:1 width to depth. Prevents 3-point adhesion. Slightly oversized for compression.
Technical Properties
- Maintains correct 2:1 width-to-depth sealant aspect ratio, preventing three-sided adhesion
- Reduces sealant volume required — improves economy on long joint runs
Limitations
- Over-sized backer rod stretches and may crack the sealant — diameter selection is critical
- Closed-cell type only with silicone sealants — open-cell causes off-gassing and bubbling
PROCUREMENT SOURCES
System Description
Insert to control sealant depth at 1:1 width to depth. Prevents 3-point adhesion. Slightly oversized for compression.
Technical Properties
- Maintains correct 2:1 width-to-depth sealant aspect ratio, preventing three-sided adhesion
- Reduces sealant volume required — improves economy on long joint runs
Limitations
- Over-sized backer rod stretches and may crack the sealant — diameter selection is critical
- Closed-cell type only with silicone sealants — open-cell causes off-gassing and bubbling
PROCUREMENT SOURCES
System Description
Insert to control sealant depth at 1:1 width to depth. Prevents 3-point adhesion. Slightly oversized for compression.
Technical Properties
- Maintains correct 2:1 width-to-depth sealant aspect ratio, preventing three-sided adhesion
- Reduces sealant volume required — improves economy on long joint runs
Limitations
- Over-sized backer rod stretches and may crack the sealant — diameter selection is critical
- Closed-cell type only with silicone sealants — open-cell causes off-gassing and bubbling
PROCUREMENT SOURCES
Brand Equivalents
Side-by-side view of equivalent products across all major brands.
| Material | Ardex | Sika | Fosroc | Tremco / Other | Parchem / Mapei |
|---|---|---|---|---|---|
| Backer rod (closed-cell foam) | Norseal V740 | Sika | Fosroc | Norseal V740 | Rexnord Villex |
Disclaimer
Information is general only. Product selection must be confirmed against project requirements, substrate condition, exposure class, manufacturer technical data sheets, NCC requirements, Australian Standards (including AS 3600), and consultant or structural engineer specifications. Do not rely on this reference as a substitute for professional engineering advice.
Concrete & Structural Defects
Identify defect types, causes, and repair pathways before selecting a system.
Concrete & Structural Defects
Browse all concrete and structural defect subcategories.
Concrete cracking
Browse all product categories for concrete cracking.
Generate a Scope of Works
Use the AI Scope Builder to assemble a remedial scope.