Practical Boat Owner – May 2018

When applying gelcoat to the plug, make
sure it’s not too cold and that there are no
draughts otherwise you’ll experience the
dreaded ‘allegation’ – when gelcoat
crinkles and pulls away from the surface.
You won’t always notice this and it will
only become apparent when the
component is released. It’s difficult and
sometimes impossible to repair.
Once your gelcoat is tacky and
checked for areas you may have missed
(it can still be touched up at this stage),
then you’re ready for your first, most
important layer of the mould – 450-gram

chopped strand mat.

I was always taught that a mould

needed six layers of 450g mat plus

stiffening, but as this mould wasn’t going

to get much use, I just used four layers:

one layer which was left to cure, then two

layers plus stiffening and one further layer.

For a mould which will be subject to

repeated use, it’s best to put at least five

layers down and allow it all to cure before

adding any reinforcement (plywood/PVC

foam/balsa). Reinforcement applied too

soon can cause the mould to distort or

shrink which will show through on the

finished component.

A mould should be left to cure for three

weeks before removal but because of time

constraints mine was only on for a matter

of hours – I used a heater to help cure it.

Once the mould had cured, the PVA

residue was cleaned off with water and

any slight bumps/imperfections rubbed

down. Mine was machine and hand

buffed to a dull sheen.

Once it had been cleaned again and

several layers of release wax and PVA

applied, the mould was ready for laying

up the moulding.

The mould

The mould showing panels of PVC foam reinforcement Released from the plug, here’s the mould partly cleaned

I would suggest one layer of 450g mat left
to cure then two further layers with a
reinforcement sandwich. I used one layer
less and although it’s satisfactory, it’s
probably more flexible than it needs to be.
Don’t fit reinforcement panels too close to
corner edges or it will make it difficult for
the glass cloth to bend around.

I used 5mm PVC foam reinforcement

because I had some to hand. It’s

lightweight, bonds well, is very flexible if

scored, but expensive. Lots of other material

choices are available from GRP retailers.

Once again I used a heater to speed up

the curing process.

Once the component is fully cured and

you have removed all the PVA, get it

washed off and polish it up or rub out any

slight bumps. It is now ready to be

trimmed and fitted.

At this point there’ll be a lot of fettling for

a perfect fit on the boat. It’s easy to cut

glassfibre away but almost impossible to

replace neatly, so take your time.

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

PRACTICAL

Laying up the moulding

PVA releasing agent on the fabrication

ready for cleaning off

Console moulding still in the mould,
showing reinforcement positioning

Using a ceramic heater and curing the flat

lid for the bottom access locker