The Paint Manual - Hempel

Painting substrates
Glassfibre
Glassfibre, or GRP (glass reinforced plastic), is a polyester resin
strengthened by glass fibres, making a high strength, low weight
material which requires little maintenance.
Painting glassfibre
The outer shell of the glassfibre has a
layer of gelcoat. New gelcoat contains
large residues of wax and mould-release
agents that must be removed before
painting. Use Pre-Clean or Degreaser
to remove mould release agents used in
the construction of the vessel. Abrade the
surface (150-180 grade paper). Remove
dust.
Repainting glassfibre
Over time gelcoat becomes old and
weathered. This will cause the cosmetic
appearance to deteriorate, and eventually
it will need painting to protect the surface.
Generally the deck and coach roof will
deteriorate sooner than the topsides.
The extent of the degradation depends on
many factors:
• colour and pigment of the gelcoat,
• if the gelcoat has been maintained,
• condition of where the vessel is kept
e.g. strong UV light,
• mechanical damage,
• weathering, etc.
Key Advice:
Old gelcoat will probabily still bear
residues of wax and mould-release
agents and it will be necessary to
carry out a degreasing procedure.
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Painting substrates – glassfibre