62 Practical Boat Owner t http://www.pbo.co.uk
PRACTICAL
TOP TIP
Flip the brush over on
each pass. Paint
lengthways first,
crossways second, and
lengthways again last.
This helps create a very
even coating.(^1)
The epoxy resin and hardener must
be measured out in the precise ratio,
and mixed thoroughly.
(^2)
Once mixed, we laid
down the first sheet of
carbon cloth onto the tacky
gelcoat and, using a
stippling motion, worked the
epoxy right into it. This layer
will form the attractive face
of the clipboard behind a
high gloss finish.
(^3)
Air pockets in the foam backing
reinforcement must be sealed up
before laminating.
Once the gelcoat has gone tacky, it is time
to apply the laminating epoxy that will wet
out the rest of the composite. We were
using Pro Set Lam-125, described to us
as ‘a lovely, low viscosity, easy to wet-out
laminating resin.’ Used with the Pro Set
Lam-266 Medium Hardener, the curing
time is ‘just about perfect for building a
small dinghy, allowing plenty of time for
the resin to be fully infused’.
We mixed the resin and hardener
together in a ratio described by the data
sheet as 100:28.6 by weight – yes, it really
is that precise – being careful to stir for
about two minutes to get a completely
blended mix.
The stiffening to make the board rigid
comes from a thin sheet of foam core,
which is rated by its density of 60kg/m^3.
However, when the sheet was cut from its
parent block, it left thousands of open
cells in each surface. If these became
filled with laminating epoxy, which weighs
1 ton per m^3 , it would make the board
unnecessarily heavy.
To fill the voids, an additional mix of the
same Pro Set Lam-125 resin and 266
hardener is thickened with West System
3 Adding the laminating resin
(^4)
A blend of lightweight West System
microspheres makes the ideal
lightweight filler.
409 Microspheres Blend. This low-density
filler is mixed to a peanut butter
consistency to fill up all the voids. A plastic
applicator ensures a smooth coat.
The sealed side of the foam is placed
onto the wetted-out carbon fibre, and then
the upside is filled with the same
microsphere mix.
Another layer of reinforcement, this time
a carbon/aramid hybrid fibre, is placed on
the other side to make a foam sandwich.
This is also wetted out by brush-stippling
with more laminating epoxy.
A layer of peel ply is placed over the
top, and the last of the epoxy used to
ensure it is fully wetted out.
Finally, a layer of release film is then
applied. This film is perforated to allow
excess epoxy through into the breather/
bleed-out fabric and allow the vacuum to
draw air voids out and through the
vacuum exhaust. Release film makes it
much easier to remove the breather and
vacuum bag once the laminate has cured.
“The best way to think of infusion is to
imagine a giant syringe,” said Wessex
Resin’s David Johnson. “By drawing the
air out from a mould, the earth’s
atmosphere pushes down on the epoxy
in the bucket like a giant thumb on a
plunger. This force is equivalent to 10
tonnes per square
metre so is a
highly efficient
method of
propelling the
epoxy into the
laminates to wet
every surface and
purge every void.”
David is a technical advisor to many of
the world’s leading boatbuilders, and
teaches the regular infusion seminars at
West System International’s UK office
near Southampton in Hampshire.
Delegates fly in from all over the world
to attend these two-day courses, and
we were invited to join a contingent of
professional boatbuilders from Italy.
To learn about the infusion process,
we would be using products from the
Pro Set range. Although Pro Set
laminating epoxy cures at room
temperature, the gentle application of
heat, usually just 50°C as a ‘post cure’,
will enhance the epoxy resin’s properties.
Pro Set infusion epoxy remains very
viscous for several hours during the
infusion process. As such, it lends itself
perfectly to being pushed through
millions of tiny pores within the
laminates to ensure full saturation of the
fibres. In the case of our canoe, the
mould is made with a porous centre.
Warm water is run through this core to
provide an even heat for post cure
throughout the whole of the mould.
The weight of air
David Johnson