Expandafoam Closed Cell: Technical Details, Specifications, and Features

Product Overview

Expandafoam Closed Cell is a medium density, closed cell polyethylene foam rod supplied in circular section cords of varying diameters. This product is primarily used as a bond breaker and joint profile former to support elastomeric sealants in expansion joints between all common building materials. It combines compressibility with low load transfer properties, making it an ideal backing strip and joint filler for diverse construction applications.

Material Composition and Properties

Base Material

Expandafoam Closed Cell is manufactured from closed-cell polyethylene foam, which provides the foundation for its performance characteristics. The closed-cell structure prevents water absorption and eliminates migratory chemical release, making it compatible with all elastomeric sealants.

Key Physical Properties

Property	Specification
Form	Compressible, closed cell polyethylene foam rod
Colour	White
Nominal Density	25 kg/m³
Service Temperature Range	Minus 80°C to 100°C
Water Absorption	0.01 ml/cm³
Weathering Test	No disintegration

Design Criteria and Installation

Compression Ratio

Expandafoam Closed Cell should always be installed into a joint under compression to ensure that applying the joint sealant will not displace the foam. A compression ratio of 25% is recommended when installing into a joint, or alternatively, use foam that is 1/3 larger than the joint size.

Joint Width and Diameter Selection

The appropriate diameter of Expandafoam Closed Cell is selected based on joint width using the following sizing guide:

Joint Width	Recommended Diameter
5 to 8 mm	10 mm
9 to 11 mm	13 mm
12 to 13 mm	15 mm
14 to 17 mm	20 mm
18 to 20 mm	25 mm
21 to 27 mm	30 mm
28 to 35 mm	40 mm
36 to 45 mm	50 mm

Sealant Depth Requirements

The sealant depth must be a minimum of 6 mm at the thinnest section of the sealant bead (above the centre of the Expandafoam), with a minimum bonding depth at the joint face of 6 mm on smooth glass and metal surfaces, and 12 mm on porous or rough surfaces. For larger joints, the depth of the joint face should normally be half the joint width.

Cross-Sectional Characteristics

When properly compressed during installation, Expandafoam Closed Cell assumes an oval cross section. The circular section of the foam provides a convex face that ensures applied elastomeric sealants achieve optimum shape for minimum strain as the joint moves. This design feature is critical for accommodating joint movement effectively.

Key Advantages

• Compatible with all elastomeric sealants – provides reliable support without adverse chemical interaction
• Readily compressible – accommodates various joint sizes through compression
• Low load transfer – minimizes stress transfer to adjacent building materials
• Non-gassing – does not release volatile compounds or gases
• No water absorption – maintains performance in wet conditions
• CFC free – manufactured without chlorofluorocarbon compounds
• Resistant to long-term UV exposure – maintains integrity when exposed to sunlight
• No migratory chemicals – contains no substances that could adversely affect joint sealants

Primary Applications

Roads, Bridges, and Roof Joints

Expandafoam Closed Cell is used as a backing strip for non-traffic-bearing expansion joints in roads and bridges, providing essential support for joint sealants.

External Walling and Cladding

The product functions as:

• A backing strip for expansion joints
• A gap filler for open joints prior to application of cold applied joint sealants
• A readily compressible, low load transfer joint filler in joints surrounding brick infill panel walling

Glazing

Expandafoam Closed Cell is used as a gap filler and backing strip to support perimeter sealing around frames and sub-frames.

Internal Finishes

The product provides gap filling and backing strip support for sealants in partition joints and around work tops, baths, and other internal finishes and fittings.

Expansion and Isolation Joints

Expandafoam Closed Cell is suitable for use in expansion joints, isolation joints, and as a back-up strip for elastomeric sealants in deep joints.

Installation Instructions

Application Method

When used as an expansion or isolation joint filler, Expandafoam Closed Cell should be positioned to provide for a surface sealing slot of required dimensions, ensuring that the sealing slot is free from mortar droppings, slurry, and other contaminants.

When used as a backing strip, the foam is simply push fitted back into the joint. The cord diameter used should be 20 to 30% greater than the joint width.

Installation Precautions

Sharp objects should not be used when fitting Expandafoam Closed Cell, as damage to the joint backing may allow air voids to form in the sealant, potentially compromising joint integrity. Careful fitting ensures correct sealant dimensions are maintained after installation.

Supply Specifications

Expandafoam Closed Cell is available in multiple roll lengths and diameters:

Size	Material Code
10mm x 250m roll	FC700973-UNIT
13mm x 100m roll	FC700974-UNIT
15mm x 100m roll	FC700975-UNIT
20mm x 60m roll	FC700976-UNIT
25mm x 50m roll	FC700977-UNIT
30mm x 50m roll	FC700978-UNIT
40mm x 2m strip	FC700979-UNIT
50mm x 2m strip	FC700980-UNIT

Other sizes may be available upon application. The product is supplied in sheet sizes of 2.4 m x 1.2 m for standard applications.

Limitations

• Not suitable for hot pour sealants – the foam's material properties are incompatible with heat-based applications
• Not resistant to long-term UV exposure when unprotected – requires protective covering or application of coatings
• Not suitable for applications requiring continual support – for water retaining structures or floor joints subject to traffic, Hydrocell or Stiffjoint, semi-rigid fillers, should be used instead

Storage Requirements

Expandafoam Closed Cell should be stored in dry conditions and not left exposed to the elements for extended periods, especially in hot climates. Proper storage maintains product performance and characteristics.

References

• [1] Fosroc_Expandafoam_Closed_Cell_TDS.pdf
• [2] Fosroc_Expandafoam_TDS.pdf
• [4] Fosroc_Hydrocell_TDS.pdf