Fibreglass boats
Practical Action
evenly and prevent air bubbles from getting trapped between the mat and the resin. Leave for
8-24 hours until set and cooled. Next, apply a layer of CSM. The panels of CSM should be
cut to overlap each other by 3-4 inches. Te resin should then be prepared and applied and
rolled as above. A layer of core mat may also be added sandwiched between layers of CSM.
This layered approach is to be repeated until the required thickness is achieved. Ideally the
thickness of the mould should be at least twice that of the hulls to be made using the mould.
After the fibreglass laminate has been completed, and has cured beyond the gel stage, bond
the stiffening to the outside before release from the plug. This may include a stand to raise it
off the floor. The reinforcement stiffening can be of wood, foam or rolled newspaper, which
are placed against the outer surface of the mould and covered with a layer of fibreglass to
form a box section. This will strengthen the mould and help prevent distortion. More details
on stiffening are given below. Leave the whole assembly for up to 3 weeks to become fully
cured before releasing the mould.
To release the mould from the plug, gently hammer small wooden wedges between the mould
and plug. A few blows to the flat areas with a rubber mallet can also help. Once the plug has
been removed, inspect the mould for flaws and damage and make any repairs necessary
before sanding with water sandpaper of increasingly finer grades, and polishing with 5–7
coats of wax to finish.
Plugs and moulds for deck and interior can be made using sheets of hardboard, or plywood
covered with Formica, as a plug, to provide large flat areas of decks and bulkheads with a
uniform surface. Tight corners are generally made from resin putty and sanded to shape.
Making a new hull
After the mould has been cleaned, waxed and polished, the first step in laying up a new hull
is the application of gel coat with paint rollers or paint brushes, or by spraying.
A single heavy coating of 0.6 mm thickness or 2 medium coatings of 0.5 mm each is
required on all surfaces. Paint brushes can be used to cover restricted corners. Have a follow-
up bucket of resin ready for use as soon as the first is emptied, to achieve a good bond
between the two separately mixed batches.
As soon as the gel coating is finished, start washing
hands and tools in acetone, followed by soap and
water. Brushes and rollers must be dry before re-use.
After the gel coat has cured (in 6 – 12 hrs), check for
flaws. It is important that it is not left longer than 48
hours, before being overlaid. Any rough areas on the
gel coat may need to be lightly sanded and cleaned.
Any areas that have become too dry because of
overcure can be lightly washed with styrene to regain
some stickiness.
The mat now needs to be laid in either a fore and aft
(forward and back) direction or transversely (across).
The fore and aft option is recommended as it is faster.
A sequence should be worked out so that the binder is
dissolving in CSM laid in one part of the mould, while
previously laid CSM with now dissolved binder is
Credit: Practical Action South Asia
being consolidated in another part. While a layer is
curing in one side of the mould, the other side can be worked on. This allows application of
resin and reinforcement, consolidating and curing to take place in rotation. Always apply resin
before mat. Usually, one layer of satin mat and then CSM is laid up for 1 or 2 layers next to
the gel coat. Subsequent layers should be applied as soon as the resin hardens. These
subsequent layers may be strengthened by the inclusion of a cloth or WR layer which can be
laid in the mould at the same time as CSM and which are consolidated together. This saves
time and achieves a better bond since both layers of reinforcement are using the same batch
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