Fibreglass boats
Practical Action
Glass fibre
Glass is processed into filaments then woven or chopped and supplied in rolls of matting. The
thickness of the cloth or mat varies with the weight of the glass in grams per square metre.
Type E glass should be used for tropical marine use. Reinforcement materials are supplied in
rolls sealed in polythene bags inside cardboard boxes. On delivery the material should be
checked for contamination by dirt, oil or water. If spoiled, it is unusable. After checking, the
rolls, they should be re-sealed to prevent contamination by high humidity. If damp, the
bonding between the resin and mat are weakened.
Chopped strand mat (CSM)
The continuous filament is held together with a binder to form a continuous sheet of chopped
strand mat of variable thickness. This material is specified by weight: 225, 300, 450 and
600 g/m2. One side of the material is slightly smoother than the other. It is the rougher side
which should be placed down when laminating.
Woven roving (WR)
Standard specifications for WR are 600 g/m2 and 800 g/m2. WR has a high tensile strength
and also gives a higher glass per unit volume ratio than CSM, which means less resin is
needed, and therefore is cheaper to use. Approximate resin to glass ratio for CSM is 2.5:1 by
weight (30% glass) and for WR is 1.25:1 (45% glass).
WR is rarely used in vessels of less than 6 m. CSM laminates are normally adequate for
smaller boats. Laminates for larger hull are best made of alternate layers of CSM and WR with
extra CSM near the outside.
Surface tissue / satin mat
This is very thin and can be compared to a very fine, smooth CSM. It is used to support a
thick gel coat or to produce a smooth finish on the innermost layer of a laminate.
Core mat
This is a course mat that is specified by thickness rather than weight. 2 – 5 mm core mat is
available. It is used only for specific areas which require extra strengthening.
Resins
All resins should be stored in a cool, shaded and ventilated place. The usual shelf life for
resin is given as 6–12 months, but it can be used as long as it is liquid. Pre-accelerated
resins have a shorter shelf life than pure resin.
Lay-up or laminating resins
The laminating resin (a translucent liquid of pale
colour) provides the medium within which the
fibreglass mat is bedded. “Marine General Purpose”
resin, which has been previously approved by a
Classification Society such as Bureau Veritas or
Lloyds Register of Shipping, should be used. The
resin is usually supplied in 200-litre drums, but can
also be bought in smaller quantities from retail
suppliers.
Gel coat resin
The gel coat resin is a more viscous liquid. When
cured, the gel coat forms the shiny, smooth, weather
resistant outer surface of the hull.
Credit: Practical Action
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