Hand lay-up (HLU) – also called contact moulding – is the oldest, the simplest and still most spread technology. HLU belongs to so called open technologies. The mould (negative-female or positive-male) is first provide with release agent and subsequently very often with gelcoat.
Gelcoat is specially formulated, mostly pigmented non-reinforced surface layer with 0.3-1 mm thickness. It is applied either by hand with brush or hair roller or by spraying. Gelcoat provides the aesthetic point of view and creates the protection against environmental impacts (water, weather, chemicals).
When the gelcoat is partly cured (non-liquid, but still sticky) the laying of reinforcing material can start. Individual reinforcing layers are properly impregnated by initiated resin by brush or the matrix is applied by hair roller, excess resin and air bubbles are removed by fin or paddle rollers.
The laminate is cured by normal temperature mostly without applying of pressure, only in the case when it is necessary to build up the sandwich structure using lightweight core materials (foams, honeycombs etc.) vacuum pressure under the foil is used.
Curing some types of resin by the elevated temperature is recommendable to enhance their thermal resistance keeping the step by step temperature increase schedule.