Glass-fibre facers for building boards

[edit] Introduction

A glass-fibre facer is a facing layer incorporated into a building board or panel. It is distinct from the board core and from the complete installed building element. Depending on its construction and intended use, a facer can provide a surface for finishing, an interface with the core, or a contribution to handling and other product requirements.

Glass-fibre mats are used as facers for applications including gypsum boards, ceiling products and mineral-wool or foam insulation products. Glass fibre is also used in a range of other construction materials and applications.

The term facer describes the role of the material rather than providing a complete material specification. Two materials used for facing applications may differ in fibre arrangement, binder, coating, reinforcement and surface treatment. The material description therefore needs to be considered alongside its construction and intended application.

[edit] Material forms and terminology

A nonwoven glass mat consists of glass fibres held together without being woven into a regular fabric. In board-facing applications, terms such as glass mat, glass veil and glass nonwoven may be used. These descriptions do not establish that products with different constructions are interchangeable.

A coated glass mat incorporates an additional surface treatment or coating. The nature of the coating and its purpose can vary according to the application. A woven glass fabric, open reinforcement and nonwoven mat should not be treated as equivalent simply because each contains glass fibre. A specification should identify the substrate and any additional layers and, where relevant, the surface intended to contact the board core, adhesive or finish.

There is also an important distinction between a facer and a glass-mat-faced board. A facer is a material layer, whereas a faced board is a manufactured product incorporating a core and one or more facings. The specification or classification of a finished board cannot automatically be applied to an unfixed roll of facer, or vice versa.

[edit] Functions in different board applications

[edit] Gypsum boards

Glass mats can be used on the front and back of gypsum boards. The facer may contribute to bonding with the core and to the manufacturing process, including interaction with gypsum slurry and drying conditions.

The suitability of a particular facer depends on the board construction and manufacturing conditions for which it is selected. Evaluation should therefore identify the intended gypsum-board product, the required interface with the core and the relevant process conditions. Describing a material simply as a gypsum facer does not establish compatibility with every board formulation or manufacturing process.

[edit] Acoustic ceiling and wall products

In ceiling and wall products, a glass-fibre facing can form the visible surface and contribute to characteristics of the finished product. Its performance therefore needs to be considered in relation to the complete acoustic construction rather than solely as a decorative layer.

Airflow-related material data should not be confused with sound-absorption performance. Airflow resistance is a property associated with the movement of air through a porous material, whereas sound absorption is assessed using different measurement methods and depends on the construction in which the material is incorporated. A facer name, colour or nominal mass per unit area does not establish a sound-absorption coefficient for a finished ceiling or wall panel.

For specification purposes, acoustic evidence should identify the tested product and construction arrangement and the method used to obtain the reported result.

[edit] Mineral-wool and rigid-foam insulation

Glass-fibre facers are also used with mineral-wool and foam insulation products. Requirements may include adhesion to the insulation core, dimensional stability during lamination and controlled interaction between the facer and other layers.

Such requirements relate to particular material and process combinations and should not be assumed to apply to every faced insulation product. Material-process suitability should therefore be distinguished from the in-service performance requirements of the finished product. A successful lamination trial provides evidence for the conditions tested, but does not by itself demonstrate all the moisture, mechanical, fire or other performance characteristics required of the finished product.

[edit] Information needed for material selection

A useful facer specification links the material description to the function it is expected to perform. The following is an evaluation checklist rather than a universal set of acceptance criteria.

Mass per unit area can help identify a material, but does not describe its complete construction. Comparing two facers solely because they have the same nominal mass can overlook differences in substrate, coating, fibre arrangement and other characteristics.

Where mechanical test results distinguish machine direction and cross direction, those designations should be retained and the specimen orientation established. A directional tensile result should not be used as evidence of airflow or water-vapour behaviour. The test configuration and property being measured should be established before numerical results are compared.

[edit] Performance evidence and its limits

An air-permeability measurement describes airflow through the tested specimen under specified conditions. Water-vapour transmission testing concerns a different transport process and should not be treated as a measurement of air leakage.

Fire-performance classifications also need to be considered in their proper context. EN 13501-1 provides a system for classifying the reaction to fire of construction products using specified test data and considering their intended end use. A classification therefore needs to be read alongside the product description and the scope of the relevant classification. It should not be assumed to transfer automatically to another board incorporating a similar-looking facing.

The same principle applies to claims concerning moisture resistance, durability and cleanability. The relevant exposure, test method and product should be identified. The presence of glass fibre alone is not sufficient evidence for an unrestricted performance claim.

A technical data sheet, laboratory report and application-trial record serve different purposes. They should be considered together without treating one type of evidence as proof of characteristics that it was not designed to establish. Typical or indicative data should not be converted into a guaranteed acceptance limit unless that limit has been specifically agreed.

[edit] Receipt, trial records and substitution

Before a roll of facer is used in a manufacturing trial, the receiving record should identify the material and its condition. Useful observations can include packaging, roll identification, edges, winding, visible surface condition and the applicable document version.

The subsequent trial record should connect these observations with the board construction, process conditions and outcome. This can help distinguish a material change from a process change rather than attributing every difference to the facer.

A proposed substitute should be assessed against the functions and evidence required by the existing specification. Similar appearance, nominal weight or generic material terminology does not demonstrate equivalence.

Any decision to accept a change should identify the properties that have been compared, the application conditions that have been checked and the end-use evidence that remains applicable.

[edit] Specification principle

A glass-fibre facer should be specified as an identified layer performing defined functions within a particular product. Selection is most reliable when the material description, processing requirements and end-use evidence remain connected, while the facer, finished board and installed assembly remain clearly distinguished.

[edit] Related articles on Designing Buildings

• Glass fibre
• Glass wool blanket
• Glass wool v reflective foil insulation
• Glass reinforced concrete
• Glass reinforced plastic GRP
• Types of cladding
• Types of cladding index
• Glass for buildings