Fig 13 shows the hand lay-up process used to make a glass-reinforced plastic (GRP) product. The cross-section shows layers of material being built up inside...

(a) The substance applied to the mould surface before the lay-up begins (layer A) is a release agent (mould release agent). [1] The release agent creates a thin non-stick barrier between the mould and the first layer of resin, ensuring the cured laminate can be removed cleanly from the mould without sticking or damaging either the product or the mould surface.

(b) The materials labelled B and C: [2]

• B = Polyester resin (or epoxy resin) [1] - this is the matrix material that saturates and binds the reinforcement fibres.
• C = Glass fibre matting (chopped strand mat / glass fibre cloth) [1] - this is the reinforcement material that provides tensile strength and stiffness to the composite.

The layers alternate: resin, then glass fibre mat, then resin, then another mat, building up the required thickness.

(c) The roller is used during the lay-up process for two reasons: [2]

1. It presses the resin thoroughly into the glass fibre matting to ensure the fibres are fully wetted out (saturated with resin), creating a strong bond between the matrix and reinforcement throughout every layer. [1]
2. It removes trapped air bubbles from between the layers. Air pockets would create voids (weak spots) in the finished laminate where the fibre and resin are not bonded, which could lead to delamination or cracking under load. [1]