Class A surface

The highest standard of visible exterior surface finish, a term used mainly in the automotive industry to denote panels free from waviness, print-through and defects when inspected under critical lighting. Achieving it in composites drives choices such as tooling quality, low-shrink resin systems and surfacing films.

Also known as: Class A finish, A-surface

Related terms

Gelcoat

A pigmented, resin-rich surface coat applied to the mould face before laminating, which cures to form the smooth, weather-resistant outer surface of a GRP moulding. It protects the underlying laminate from moisture and UV exposure and provides the colour and gloss of the finished part.

Composites & laminatesCoatings & protectionMarineConstructionAutomotiveIndustrialGreen energy

Print-through

A surface defect in which the pattern of the underlying reinforcement or core becomes visible on the finished face of a moulding, usually as a result of resin shrinkage during cure or post-cure. It is a particular concern on high-gloss gelcoated and painted panels.

Composites & laminatesMarineAutomotiveIndustrialGreen energy

Sheet moulding compound

SMC

A ready-to-mould sheet of chopped glass or carbon fibre, mineral filler and thermosetting resin, compression moulded under heat and pressure into stiff parts with good surface finish. SMC is widely used for vehicle body panels, electrical enclosures and building components.

Composites & laminatesManufacturing processesAutomotiveIndustrialConstruction

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