Practical Boat Owner – May 2018

Practical Boat Owner t http://www.pbo.co.uk 63

EPOXY VACUUM INFUSION

Perspex sheet

Release wax (over whole sheet)

Masking tape (removed after

application of gelcoat)

Gelcoat

Laminating resin

Carbon fibre

Filler (on underside of core)

Foam core

Filler (on top side of core)

Aramid/carbon hybrid

Peel ply

Release film

Breather fabric (2 layers)

Breather pad (folded)

Lower hose attachment

Vacuum bag

Connector puck

1 2 3 4 5 6 7 8 9

10

11

12

13

14

15

16

17

Layer under the vacuum bag for a

foam cored panel

(in order of being laid down)

Bagging

tape

Vacuum bag

17

16

15

14

12

9

10

6

5

4

2

1

3

13

11

8

7

The importance of pleats

One of the trickiest aspects of vacuum

bagging is how to make pleats in the bag so

that the plastic is able to contract around the

sandwich without ‘bridging’ whilst also

preserving its airtight integrity.

A bag without pleats will be unable to be

sucked down into the various corners and

walls to ensure full consolidation, so the

laminate will be compromised.

It’s very common for the

circular punching created

when the two halves are

screwed together to block

the pipe. The punching can

be easily removed by

dabbing it out with the corner

of a piece of exposed vac

bag sealant tape.

Two layers of a soft breather fabric are
placed on top of the release fi lm, with a
third folded pad under the connector
puck. A border made from fl ash tape is
then added where the vacuum bag
sealant tape will go, to make it easier to
remove later.
Vacuum bag sealant tape is a heavy
paste-like material supplied in a roll
between two paper strips. These strips are
peeled away to reveal the sticky surface.
The tape is fi rst applied as a border,
preferably on top of fl ash tape, and then

the bag is assembled over the top (see

panel, below right).

With the bag positioned over the work,

the upper protective layer of each border

of bag tape is peeled back, and the bag

stuck down, with two or three pleats

folded into each side.

Before the bag is fully sealed down, the

puck of the vacuum attachment point is

placed under the centre of the bag,

resting on its own pad of breather fabric.

The outer part of the through-bag

connector is then screwed into place.

Once the bag is fully assembled, the

vacuum pump is switched on and

atmospheric pressure gets to work. You’ll

need to listen to the bag carefully to hear if

is air is being sucked in, especially around

the pleats. Knead the bag tape to seal

leaky joints as necessary.

The epoxy will penetrate right through

the laminates. Once the vacuum has been

made, the air valve can be closed and the

vacuum pump switched off. The epoxy will

now cure. Our clipboards were left under

vacuum overnight.

1

Pleats are made using an extra piece
of bagging tape. Watch for
weaknesses in airtight integrity.

2

The following morning the bags were

released, and the fi lm pulled away

from the back of the laminate.

3

The resulting moulding was

incredibly light with a high gloss

fi nish and a roughened back.

4 Assembling the bag

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