Fibreglass boats
Practical Action
Wood
Wood should be roughened, dry, dust free, unpainted and given as big a contact area as
possible. Resin thinned with 10% styrene or 5% acetone will allow a keying coat to better
penetrate a wood surface. Any wood that has been treated with preservative should not be
used, but if unavoidable then a joint using screws or bolts should be substituted. Oily
hardwoods such as teak should be degreased with acetone and the moisture content of all
woods checked before use. De-bonding of Fibreglass angles securing structural members,
such as bulkheads and frames, is a common problem. De-lamination through resin
contamination or movement caused by wood shrinkage will make the joint useless. Epoxy
resin has better adhesive qualities.
Metal
Some metals accelerate gelling time; others slow it down. Copper should be avoided.
Brass or bronze fittings should be coated with epoxy resin before being overlaid with any
structural resin. Aluminium and steel are best etch primed before coating. All metals should
be de-greased before use, even finger marks or sweat from a hand can make the bond
ineffective. Roughened surfaces provide better keying. It is best to avoid metal to wet resin
joints, because if the metal corrodes, it may cause delamination and leaks.
Other materials
Glass, polythene, formica, aluminium and the like will not bond and can be used to mould
flat panels of Fibreglass. Cardboard, hardboard, cement, and canvas all have rough porous
surfaces and will give some degree of bonding.
Using tools on fibreglass mouldings
Metalworking rather than woodworking tools should be used. Fibreglass can be drilled, filed,
sawn and polished but not hammered or bent and not easily punched or sheared. The basic
shape cannot be altered and the resin component shows a tendency to fracture and chip.
Drilling
Holes can be drilled easily with ordinary twist drills. Wherever possible drill from the smooth
face towards the rough side as this prevents chipping the resin-rich gel coat. Masking tape or
a punched mark will help prevent scratch marks from skidding drills if a hole has to be drilled
from the gel coat side. For large holes use a tank cutter or hole saw or drill perforations
around the circumference of a large hole with a drill bit wide enough to accept a jigsaw blade,
then saw it out.
Sawing
A hacksaw, pad saw or jigsaw should be used for sawing and trimming. Always saw on the
face opposite the gel coat to avoid chipping. Heavy-duty electric jigsaws with metal cutting
blades or diamond wheel compressed air cutters are the most effective.
Filing
Fibreglass files easily. An open pattern file is less liable to clog particularly when the resin is
not fully hard. On edges, the cutting stroke should be in the direction away from the gel coat
once again to avoid chipping.
Hammering
Hammered fastenings or blows with a metal hammer will shatter the laminate.
Sanding
“Wet and dry” (black colour) sandpaper is the only suitable kind, and it must be used with
plenty of water. A small amount of liquid soap added to the water will reduce friction. For
power sanding, a very open grade of disc will clog least. Resin bonded discs must be used.
Facemasks should be worn and dust removed before applying the next layer.
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