Practical Boat Owner – May 2018

Practical Boat Owner t http://www.pbo.co.uk 61

EPOXY VACUUM INFUSION

The Pro Set gelcoat is applied to the

surface at a thickness equivalent to a

couple of business cards

Mastering the basics: making a flat sheet of composite

1 Moulding release prep

2 Applying the gelcoat epoxy

To illustrate just how vacuum
consolidation works when wet laminating,
students tackle a small-scale project first

• an ultra-lightweight clipboard that they’ll
  be able to take home as a souvenir.
  This wet lay and vacuum bag technique
  would prove perfect for up-scaling to other
  DIY jobs, such as a washboard, a deck
  hatch or an entire bulkhead. All you would
  need is a flat board of the right size to
  laminate against, and a pump capable of
  creating (and holding) enough vacuum
  during the epoxy’s initial cure time. All the
  skills learnt here would be needed when
  we came to build the canoe.

The item you are making within a mould is
referred to as a ‘moulding’ and to make
sure it can pop out cleanly once cured,
the mould itself needs to be smooth and
have a release agent applied. The mould
for our clipboard was a rigid sheet of
Perspex, which would create the flat
surface of the finished moulding.
Delegates were also supplied with some
release wax, a sponge and two cloths.
The waxing process is most effective on
a high gloss surface, hence the shiny
Perspex. A highly polished surface will
also result in a glossy finish to the
moulding. Special Mirrorglaze mould
release wax made by Meguiar was
applied with a sponge, and rubbed as a
thin layer over the entire sheet. Excess
was then removed with a green ‘wax off’
cloth to leave an even film of wax.

1

Waxing the mould for later release of

the moulding is a key stage that

should be carried out methodically.

2

Only use a specially formulated

silicon-free wax for mould release –

don’t be tempted by household waxes.

This layer of wax was then polished with

a different, blue polishing cloth. We were

encouraged to polish hard, as this would

generate some heat that would cause the

A border of masking tape is applied
slightly larger than the finished size of the
clipboard. This will guide the application
of the epoxy gelcoat and ensure that none
is painted onto the border later used by
the vacuum bag tape.
Pro Set gelcoat is a mix of epoxy resin
and its dedicated epoxy hardener in
exactly the right ratios. We would be using
the Pro Set M1044 Translucent Gelcoat
Epoxy Resin with a ‘medium speed’
hardener, M2048. Exactly 50g of gelcoat
resin was mixed with 15g of hardener.
Unlike with polyester resin, there is no
room for altering this ratio, and to do so
would only compromise the cure. The
resin and hardener are thoroughly mixed
together for at least two minutes before
being painted on to the surface.
A pair of digital kitchen scales is ideal
for the weight ratio measurements. A
calculator is also handy as not all ratios
are straightforward.

wax to melt slightly and so give a better

coverage. This process was repeated

three times to build up three layers of

polished wax.

The gelcoat is painted on to the waxed

surface to a depth of about 300 microns

• equivalent to the thickness of two
  business cards. Care is taken to create a
  nice, even coat, as if we were applying a
  gloss finish to a hull. In larger infusions, a
  pipe would introduce the resin.
  The masking tape is removed
  immediately afterwards to leave a clean
  edge to the gelcoat.

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Only use a silicon-free

wax specially formulated for

mould release. Simply using

a cheaper household brand,

especially if it contains any

trace of silicon, will

cause the surface of

the moulding

to blemish.

Brushes used for epoxy work are

usually disposable so tend to be

cheap. Unfortunately, cheap usually

means poor quality so hairs often

detach from the brush into your work.

To minimize this, simply nip up the

ferrule beforehand in either a vice or a

pair of mole grips.

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